1) Laser operation was achieved in a neodymium-doped scandium silicate (Nd:SSO) crystal based on the 4F3/2→4I9/2 transition of Nd3+ ions. Pumped by an 808 nm laser diode, laser emission at 914 nm was obtained with an output power of 581 mW.
2) Spectroscopic measurements of the Nd:SSO crystal found absorption and emission cross sections of 1.69×10-20 cm2 and 1.13×10-20 cm2 respectively at relevant wavelengths. The gain cross section was estimated to allow lasing inversion at β=0.25.
3) Compared to other
Copper (775) - an optics, 2PPE, and Bulk state simulation studyPo-Chun Yeh
My earlier studies on Cu(775) - a tilt cut highly crystalline copper surface using ultrafast femtosecond laser based 2-photon photoemission and its related simulation via Fortran 77.
Flexible and Ultrasoft Inorganic 1D Semiconductor and Heterostructure Systems...Pawan Kumar
Low dimensionality and high flexibility are key demands for flexible electronic semiconductor devices. SnIP, the first atomic-scale double helical semiconductor combines structural anisotropy and robustness with exceptional electronic properties. The benefit of the double helix, combined with a diverse structure on the nanoscale, ranging from strong covalent bonding to weak van der Waals interactions, and the large structure and property anisotropy offer substantial potential for applications in energy conversion and water splitting. It represents the next logical step in downscaling the inorganic semiconductors from classical 3D systems, via 2D semiconductors like MXenes or transition metal dichalcogenides, to the first downsizeable, polymer-like atomic-scale 1D semiconductor SnIP. SnIP shows intriguing mechanical properties featuring a bulk modulus three times lower than any IV, III-V, or II-VI semiconductor. In situ bending tests substantiate that pure SnIP fibers can be bent without an effect on their bonding properties. Organic and inorganic hybrids are prepared illustrating that SnIP is a candidate to fabricate flexible 1D composites for energy conversion and water splitting applications. SnIP@C3N4 hybrid forms an unusual soft material core–shell topology with graphenic carbon nitride wrapping around SnIP. A 1D van der Waals heterostructure is formed capable of performing effective water splitting.
Harvesting Hot Holes in Plasmon-Coupled Ultrathin Photoanodes for High-Perfor...Pawan Kumar
The harvesting of hot carriers produced by plasmon decay to generate electricity or drive a chemical reaction enables the reduction of the thermalization losses associated with supra-band gap photons in semiconductor photoelectrochemical (PEC) cells. Through the broadband harvesting of light, hot-carrier PEC devices also produce a sensitizing effect in heterojunctions with wide-band gap metal oxide semiconductors possessing good photostability and catalytic activity but poor absorption of visible wavelength photons. There are several reports of hot electrons in Au injected over the Schottky barrier into crystalline TiO2 and subsequently utilized to drive a chemical reaction but very few reports of hot hole harvesting. In this work, we demonstrate the efficient harvesting of hot holes in Au nanoparticles (Au NPs) covered with a thin layer of amorphous TiO2 (a-TiO2). Under AM1.5G 1 sun illumination, photoanodes consisting of a single layer of ∼50 nm diameter Au NPs coated with a 10 nm shell of a-TiO2 (Au@a-TiO2) generated 2.5 mA cm–2 of photocurrent in 1 M KOH under 0.6 V external bias, rising to 3.7 mA cm–2 in the presence of a hole scavenger (methanol). The quantum yield for hot-carrier-mediated photocurrent generation was estimated to be close to unity for high-energy photons (λ < 420 nm). Au@a-TiO2 photoelectrodes produced a small positive photocurrent of 0.1 mA cm–2 even at a bias of −0.6 V indicating extraction of hot holes even at a strong negative bias. These results together with density functional theory modeling and scanning Kelvin probe force microscope data indicate fast injection of hot holes from Au NPs into a-TiO2 and light harvesting performed near-exclusively by Au NPs. For comparison, Au NPs coated with a 10 nm shell of Al2O3 (Au@Al2O3) generated 0.02 mA cm–2 of photocurrent in 1 M KOH under 0.6 V external bias. These results underscore the critical role played by a-TiO2 in the extraction of holes in Au@a-TiO2 photoanodes, which is not replicated by an ordinary dielectric shell. It is also demonstrated here that an ultrathin photoanode (<100 nm in maximum thickness) can efficiently drive sunlight-driven water splitting.
Synthesis, Electrical and Optical Properties of Nickel Sulphate Hexa Hydrate ...IJERA Editor
L-Arginine doped Nickel SulphateHexa Hydrate (NSH) single crystalswere grown by slow evaporation
techniquefor different molar concentrations, viz., (0.2 to 1 mole% in steps of 0.2).The grown crystals were
subjected to various studies.XRD data were collected from powder samples of the crystals.ACelectrical
measurementswerecarriedoutatvarioustemperaturesrangingfrom40-750C. Resultsindicate anincrease
oftheelectricalparameterswiththeincreaseoftemperature.The dielectric value suggests that the L-Arginine doped
NSH single crystal is good for microelectronic application. The UV-Vis-NIR spectral studies were performed to
analyze the optical absorption of the grown crystals in the range 200 – 1100nm. Results obtained were
presented.
This research, presented at the 2014 APS March Meeting in Denver, Colorado, characterizes magnetic phase transitions in the manganese-doped dichalcogenide TaS2.
Copper (775) - an optics, 2PPE, and Bulk state simulation studyPo-Chun Yeh
My earlier studies on Cu(775) - a tilt cut highly crystalline copper surface using ultrafast femtosecond laser based 2-photon photoemission and its related simulation via Fortran 77.
Flexible and Ultrasoft Inorganic 1D Semiconductor and Heterostructure Systems...Pawan Kumar
Low dimensionality and high flexibility are key demands for flexible electronic semiconductor devices. SnIP, the first atomic-scale double helical semiconductor combines structural anisotropy and robustness with exceptional electronic properties. The benefit of the double helix, combined with a diverse structure on the nanoscale, ranging from strong covalent bonding to weak van der Waals interactions, and the large structure and property anisotropy offer substantial potential for applications in energy conversion and water splitting. It represents the next logical step in downscaling the inorganic semiconductors from classical 3D systems, via 2D semiconductors like MXenes or transition metal dichalcogenides, to the first downsizeable, polymer-like atomic-scale 1D semiconductor SnIP. SnIP shows intriguing mechanical properties featuring a bulk modulus three times lower than any IV, III-V, or II-VI semiconductor. In situ bending tests substantiate that pure SnIP fibers can be bent without an effect on their bonding properties. Organic and inorganic hybrids are prepared illustrating that SnIP is a candidate to fabricate flexible 1D composites for energy conversion and water splitting applications. SnIP@C3N4 hybrid forms an unusual soft material core–shell topology with graphenic carbon nitride wrapping around SnIP. A 1D van der Waals heterostructure is formed capable of performing effective water splitting.
Harvesting Hot Holes in Plasmon-Coupled Ultrathin Photoanodes for High-Perfor...Pawan Kumar
The harvesting of hot carriers produced by plasmon decay to generate electricity or drive a chemical reaction enables the reduction of the thermalization losses associated with supra-band gap photons in semiconductor photoelectrochemical (PEC) cells. Through the broadband harvesting of light, hot-carrier PEC devices also produce a sensitizing effect in heterojunctions with wide-band gap metal oxide semiconductors possessing good photostability and catalytic activity but poor absorption of visible wavelength photons. There are several reports of hot electrons in Au injected over the Schottky barrier into crystalline TiO2 and subsequently utilized to drive a chemical reaction but very few reports of hot hole harvesting. In this work, we demonstrate the efficient harvesting of hot holes in Au nanoparticles (Au NPs) covered with a thin layer of amorphous TiO2 (a-TiO2). Under AM1.5G 1 sun illumination, photoanodes consisting of a single layer of ∼50 nm diameter Au NPs coated with a 10 nm shell of a-TiO2 (Au@a-TiO2) generated 2.5 mA cm–2 of photocurrent in 1 M KOH under 0.6 V external bias, rising to 3.7 mA cm–2 in the presence of a hole scavenger (methanol). The quantum yield for hot-carrier-mediated photocurrent generation was estimated to be close to unity for high-energy photons (λ < 420 nm). Au@a-TiO2 photoelectrodes produced a small positive photocurrent of 0.1 mA cm–2 even at a bias of −0.6 V indicating extraction of hot holes even at a strong negative bias. These results together with density functional theory modeling and scanning Kelvin probe force microscope data indicate fast injection of hot holes from Au NPs into a-TiO2 and light harvesting performed near-exclusively by Au NPs. For comparison, Au NPs coated with a 10 nm shell of Al2O3 (Au@Al2O3) generated 0.02 mA cm–2 of photocurrent in 1 M KOH under 0.6 V external bias. These results underscore the critical role played by a-TiO2 in the extraction of holes in Au@a-TiO2 photoanodes, which is not replicated by an ordinary dielectric shell. It is also demonstrated here that an ultrathin photoanode (<100 nm in maximum thickness) can efficiently drive sunlight-driven water splitting.
Synthesis, Electrical and Optical Properties of Nickel Sulphate Hexa Hydrate ...IJERA Editor
L-Arginine doped Nickel SulphateHexa Hydrate (NSH) single crystalswere grown by slow evaporation
techniquefor different molar concentrations, viz., (0.2 to 1 mole% in steps of 0.2).The grown crystals were
subjected to various studies.XRD data were collected from powder samples of the crystals.ACelectrical
measurementswerecarriedoutatvarioustemperaturesrangingfrom40-750C. Resultsindicate anincrease
oftheelectricalparameterswiththeincreaseoftemperature.The dielectric value suggests that the L-Arginine doped
NSH single crystal is good for microelectronic application. The UV-Vis-NIR spectral studies were performed to
analyze the optical absorption of the grown crystals in the range 200 – 1100nm. Results obtained were
presented.
This research, presented at the 2014 APS March Meeting in Denver, Colorado, characterizes magnetic phase transitions in the manganese-doped dichalcogenide TaS2.
Asymmetric Multipole Plasmon-Mediated Catalysis Shifts the Product Selectivit...Pawan Kumar
Cu/TiO2 is a well-known photocatalyst for the photocatalytic transformation of CO2 into methane. The formation of C2+ products such as ethane and ethanol rather than methane is more interesting due to their higher energy density and economic value, but the formation of C–C bonds is currently a major challenge in CO2 photoreduction. In this context, we report the dominant formation of a C2 product, namely, ethane, from the gas-phase photoreduction of CO2 using TiO2 nanotube arrays (TNTAs) decorated with large-sized (80–200 nm) Ag and Cu nanoparticles without the use of a sacrificial agent or hole scavenger. Isotope-labeled mass spectrometry was used to verify the origin and identity of the reaction products. Under 2 h AM1.5G 1-sun illumination, the total rate of hydrocarbon production (methane + ethane) was highest for AgCu-TNTA with a total CxH2x+2 rate of 23.88 μmol g–1 h–1. Under identical conditions, the CxH2x+2 production rates for Ag-TNTA and Cu-TNTA were 6.54 and 1.39 μmol g–1 h–1, respectively. The ethane selectivity was the highest for AgCu-TNTA with 60.7%, while the ethane selectivity was found to be 15.9 and 10% for the Ag-TNTA and Cu-TNTA, respectively. Adjacent adsorption sites in our photocatalyst develop an asymmetric charge distribution due to quadrupole resonances in large metal nanoparticles and multipole resonances in Ag–Cu heterodimers. Such an asymmetric charge distribution decreases adsorbate–adsorbate repulsion and facilitates C–C coupling of reaction intermediates, which otherwise occurs poorly in TNTAs decorated with small metal nanoparticles.
Electron transfer between methyl viologen radicals and graphene oxidekamatlab
Methyl viologen radicals are capable of transferring electrons to graphene oxide and partially restore the sp2 network. The reduced graphene oxide serves as a scaffold to anchor Ag nanoparticles. The growth of these silver nanoparticles is dictated by the ability of RGO to store and shuttle electrons. The RGO/Ag nanocomposites discussed in the present work offer new opportunities to design next generation photocatalysts.
Visit our website, KamatLab.com, for the latest news, publications, and research from our group.
Noble Metal Free, Visible Light Driven Photocatalysis Using TiO2 Nanotube Arr...Pawan Kumar
Bulk g-C3N4 is an earth-abundant, easily synthesizable, and exceptionally stable photocatalyst with an electronic bandgap of 2.7 eV. Herein, the concepts of P-doping and size quantization are combined to synthesize highly fluorescent P-doped carbon nitride quantum dots (CNPQDs) with a bandgap of 2.1 eV. CNPQDs are hosted on anatase-phase and rutile-phase TiO2 nanotube array scaffolds, and examined as photoanodes for sunlight-driven water-splitting and as photocatalysts for surface catalytic reactions. Square-shaped rutile phase TiO2 nanotube arrays (STNAs) decorated with CNPQDs (CNPQD-STNA) generate 2.54 mA cm−2 photocurrent under AM1.5 G simulated sunlight. A champion hydrogen evolution rate of 22 µmol h−1 corresponds to a Faradaic efficiency of 93.2%. In conjunction with Ag nanoparticles (NPs), the CNPQD-STNA hybrid is also found to be an excellent plexcitonic photocatalyst for the visible light-driven transformation of 4-nitrobenzenethiol (4-NBT) to dimercaptoazobenzene (DMAB), producing reaction completion at a laser power of 1 mW (532 nm) while Ag NP/TNA and Ag NP/STNA photocatalysts cannot complete this transformation even at 10 mW laser power. The results point the way forward for photochemically robust, noble metal free, visible light harvesting photoacatalysts based on nanostructured heterojunctions of graphenic frameworks with TiO2.
Mixed-Valence Single-Atom Catalyst Derived from Functionalized GraphenePawan Kumar
Single-atom catalysts (SACs) aim at bridging the gap between homogeneous and heterogeneous catalysis. The challenge is the development of materials with ligands enabling coordination of metal atoms in different valence states, and preventing leaching or nanoparticle formation. Graphene functionalized with nitrile groups (cyanographene) is herein employed for the robust coordination of Cu(II) ions, which are partially reduced to Cu(I) due to graphene-induced charge transfer. Inspired by nature's selection of Cu(I) in enzymes for oxygen activation, this 2D mixed-valence SAC performs flawlessly in two O2-mediated reactions: the oxidative coupling of amines and the oxidation of benzylic CH bonds toward high-value pharmaceutical synthons. High conversions (up to 98%), selectivities (up to 99%), and recyclability are attained with very low metal loadings in the reaction. The synergistic effect of Cu(II) and Cu(I) is the essential part in the reaction mechanism. The developed strategy opens the door to a broad portfolio of other SACs via their coordination to various functional groups of graphene, as demonstrated by successful entrapment of FeIII/FeII single atoms to carboxy-graphene.
C3N5: A Low Bandgap Semiconductor Containing an Azo-linked Carbon Nitride Fra...Pawan Kumar
Modification of carbon nitride based polymeric 2D materials for tailoring their optical, electronic and chemical properties for various applications has gained significant interest. The present report demonstrates the synthesis of a novel modified carbon nitride framework with a remarkable 3:5 C:N stoichiometry (C3N5) and an electronic bandgap of 1.76 eV, by thermal deammoniation of the melem hydrazine precursor. Characterization revealed that in the C3N5 polymer, two s-heptazine units are bridged together with azo linkage, which constitutes an entirely new and different bonding fashion from g-C3N4 where three heptazine units are linked together with tertiary nitrogen. Extended conjugation due to overlap of azo nitrogens and increased electron density on heptazine nucleus due to the aromatic π network of heptazine units lead to an upward shift of the valence band maximum resulting in bandgap reduction down to 1.76 eV. XRD, He-ion imaging, HR-TEM, EELS, PL, fluorescence lifetime imaging, Raman, FTIR, TGA, KPFM, XPS, NMR and EPR clearly show that the properties of C3N5 are distinct from pristine carbon nitride (g-C3N4). When used as an electron transport layer (ETL) in MAPbBr3 based halide perovskite solar cells, C3N5 outperformed g-C3N4, in particular generating an open circuit photovoltage as high as 1.3 V, while C3N5 blended with MAxFA1–xPb(I0.85Br0.15)3 perovskite active layer achieved a photoconversion efficiency (PCE) up to 16.7%. C3N5 was also shown to be an effective visible light sensitizer for TiO2 photoanodes in photoelectrochemical water splitting. Because of its electron-rich character, the C3N5 material displayed instantaneous adsorption of methylene blue from aqueous solution reaching complete equilibrium within 10 min, which is significantly faster than pristine g-C3N4 and other carbon based materials. C3N5 coupled with plasmonic silver nanocubes promotes plasmon-exciton coinduced surface catalytic reactions reaching completion at much low laser intensity (1.0 mW) than g-C3N4, which showed sluggish performance even at high laser power (10.0 mW). The relatively narrow bandgap and 2D structure of C3N5 make it an interesting air-stable and temperature-resistant semiconductor for optoelectronic applications while its electron-rich character and intra sheet cavity make it an attractive supramolecular adsorbent for environmental applications.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
This work studied the effect of applying pulse current
(ton=off=1s) on the electrodeposition of silver nanoparticles on
carbon sphere surface as a substrate. The electrolyte is made of 0.1
M KNO3, 0.1 M KCN and 0.01M AgNO3. The pH value has been
adjusted in the alkaline region of 9.1 with the help of K(NO3)
addition. Experiments were carried out at room temperature for
periods up to 12 minutes. The cell is fitted with a mechanical stirrer
to keep the electrolyte in a dynamic state. Product(s) was
characterized with the help of SEM and EDX and field emission.
Results obtained show that silver nanoparticles has successfully
electrodeposited under pulse current conditions with a particle size
of 100–400 nm after 2 minutes. Deposition takes place on certain
accessible sites of the carbon surface of the substrate forming a
monolayer of scattered silver nanoparticles. Formation of macro
particles with larger diameter and multilayer in thickness takes
place with continuous deposition of silver nanoparticles on the
formerly deposited silver. Pulse current helps management of the
monolayer deposition as compared to the steady DC application
with respect to particle diameter and number of layers.
Photocatalytic Mechanism Control and Study of Carrier Dynamics in CdS@C3N5 Co...Pawan Kumar
We present a potential solution to the problem of extraction of photogenerated holes from CdS nanocrystals and nanowires. The nanosheet form of C3N5 is a low-band-gap (Eg = 2.03 eV), azo-linked graphenic carbon nitride framework formed by the polymerization of melem hydrazine (MHP). C3N5 nanosheets were either wrapped around CdS nanorods (NRs) following the synthesis of pristine chalcogenide or intercalated among them by an in situ synthesis protocol to form two kinds of heterostructures, CdS-MHP and CdS-MHPINS, respectively. CdS-MHP improved the photocatalytic degradation rate of 4-nitrophenol by nearly an order of magnitude in comparison to bare CdS NRs. CdS-MHP also enhanced the sunlight-driven photocatalytic activity of bare CdS NWs for the decolorization of rhodamine B (RhB) by a remarkable 300% through the improved extraction and utilization of photogenerated holes due to surface passivation. More interestingly, CdS-MHP provided reaction pathway control over RhB degradation. In the absence of scavengers, CdS-MHP degraded RhB through the N-deethylation pathway. When either hole scavenger or electron scavenger was added to the RhB solution, the photocatalytic activity of CdS-MHP remained mostly unchanged, while the degradation mechanism shifted to the chromophore cleavage (cycloreversion) pathway. We investigated the optoelectronic properties of CdS-C3N5 heterojunctions using density functional theory (DFT) simulations, finite difference time domain (FDTD) simulations, time-resolved terahertz spectroscopy (TRTS), and photoconductivity measurements. TRTS indicated high carrier mobilities >450 cm2 V–1 s–1 and carrier relaxation times >60 ps for CdS-MHP, while CdS-MHPINS exhibited much lower mobilities <150 cm2 V–1 s–1 and short carrier relaxation times <20 ps. Hysteresis in the photoconductive J–V characteristics of CdS NWs disappeared in CdS-MHP, confirming surface passivation. Dispersion-corrected DFT simulations indicated a delocalized HOMO and a LUMO localized on C3N5 in CdS-MHP. C3N5, with its extended π-conjugation and low band gap, can function as a shuttle to extract carriers and excitons in nanostructured heterojunctions, and enhance performance in optoelectronic devices. Our results demonstrate how carrier dynamics in core–shell heterostructures can be manipulated to achieve control over the reaction mechanism in photocatalysis.
A Front Surface Optimization Study for Photovoltaic ApplicationTELKOMNIKA JOURNAL
In this paper, we presented a possible front surface optical enhancement of Si solar cell by
optimizing the Antireflection (AR) and light trapping (LT) schemes. Conventional plasma enhanced
chemical vapor deposition (PECVD) and in house hot wire chemical vapor deposition (HWCVD) tool was
used to deposit Silicon Nitride (SiNX) layer and optimized at 668nm wavelength. This was followed by
surface texturing of random pyramids to further enhance the broadband reflectance of the front surface.
Broadband reflectance measurement using integrating sphere method showed achieved weighted average
reflectance (WAR) value of as low as 1.8% and 1.5%, when 85nm SiNX was deposited on top of random
pyramids structure using HWCVD and PECVD methods, respectively.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Dielectric properties of Ni-Al nano ferrites synthesized by citrate gel methodIJERA Editor
Ni–Al ferrite with composition of NiAlxFe2-xO4 (x=0.2, 0.4 0.6, and 0.8, ) were prepared by citrate gel method. The Dielectric Properties for all the samples were investigated at room temperature as a function of frequency. The Dielectric constant shows dispersion in the lower frequency region and remains almost constant at higher frequencies. The frequency dependence of dielectric loss tangent (tanδ) is found to be abnormal, giving a peak at certain frequency for mixed Ni-Al ferrites. A qualitative explanation is given for the composition and frequency dependence of the dielectric loss tangent.
Asymmetric Multipole Plasmon-Mediated Catalysis Shifts the Product Selectivit...Pawan Kumar
Cu/TiO2 is a well-known photocatalyst for the photocatalytic transformation of CO2 into methane. The formation of C2+ products such as ethane and ethanol rather than methane is more interesting due to their higher energy density and economic value, but the formation of C–C bonds is currently a major challenge in CO2 photoreduction. In this context, we report the dominant formation of a C2 product, namely, ethane, from the gas-phase photoreduction of CO2 using TiO2 nanotube arrays (TNTAs) decorated with large-sized (80–200 nm) Ag and Cu nanoparticles without the use of a sacrificial agent or hole scavenger. Isotope-labeled mass spectrometry was used to verify the origin and identity of the reaction products. Under 2 h AM1.5G 1-sun illumination, the total rate of hydrocarbon production (methane + ethane) was highest for AgCu-TNTA with a total CxH2x+2 rate of 23.88 μmol g–1 h–1. Under identical conditions, the CxH2x+2 production rates for Ag-TNTA and Cu-TNTA were 6.54 and 1.39 μmol g–1 h–1, respectively. The ethane selectivity was the highest for AgCu-TNTA with 60.7%, while the ethane selectivity was found to be 15.9 and 10% for the Ag-TNTA and Cu-TNTA, respectively. Adjacent adsorption sites in our photocatalyst develop an asymmetric charge distribution due to quadrupole resonances in large metal nanoparticles and multipole resonances in Ag–Cu heterodimers. Such an asymmetric charge distribution decreases adsorbate–adsorbate repulsion and facilitates C–C coupling of reaction intermediates, which otherwise occurs poorly in TNTAs decorated with small metal nanoparticles.
Electron transfer between methyl viologen radicals and graphene oxidekamatlab
Methyl viologen radicals are capable of transferring electrons to graphene oxide and partially restore the sp2 network. The reduced graphene oxide serves as a scaffold to anchor Ag nanoparticles. The growth of these silver nanoparticles is dictated by the ability of RGO to store and shuttle electrons. The RGO/Ag nanocomposites discussed in the present work offer new opportunities to design next generation photocatalysts.
Visit our website, KamatLab.com, for the latest news, publications, and research from our group.
Noble Metal Free, Visible Light Driven Photocatalysis Using TiO2 Nanotube Arr...Pawan Kumar
Bulk g-C3N4 is an earth-abundant, easily synthesizable, and exceptionally stable photocatalyst with an electronic bandgap of 2.7 eV. Herein, the concepts of P-doping and size quantization are combined to synthesize highly fluorescent P-doped carbon nitride quantum dots (CNPQDs) with a bandgap of 2.1 eV. CNPQDs are hosted on anatase-phase and rutile-phase TiO2 nanotube array scaffolds, and examined as photoanodes for sunlight-driven water-splitting and as photocatalysts for surface catalytic reactions. Square-shaped rutile phase TiO2 nanotube arrays (STNAs) decorated with CNPQDs (CNPQD-STNA) generate 2.54 mA cm−2 photocurrent under AM1.5 G simulated sunlight. A champion hydrogen evolution rate of 22 µmol h−1 corresponds to a Faradaic efficiency of 93.2%. In conjunction with Ag nanoparticles (NPs), the CNPQD-STNA hybrid is also found to be an excellent plexcitonic photocatalyst for the visible light-driven transformation of 4-nitrobenzenethiol (4-NBT) to dimercaptoazobenzene (DMAB), producing reaction completion at a laser power of 1 mW (532 nm) while Ag NP/TNA and Ag NP/STNA photocatalysts cannot complete this transformation even at 10 mW laser power. The results point the way forward for photochemically robust, noble metal free, visible light harvesting photoacatalysts based on nanostructured heterojunctions of graphenic frameworks with TiO2.
Mixed-Valence Single-Atom Catalyst Derived from Functionalized GraphenePawan Kumar
Single-atom catalysts (SACs) aim at bridging the gap between homogeneous and heterogeneous catalysis. The challenge is the development of materials with ligands enabling coordination of metal atoms in different valence states, and preventing leaching or nanoparticle formation. Graphene functionalized with nitrile groups (cyanographene) is herein employed for the robust coordination of Cu(II) ions, which are partially reduced to Cu(I) due to graphene-induced charge transfer. Inspired by nature's selection of Cu(I) in enzymes for oxygen activation, this 2D mixed-valence SAC performs flawlessly in two O2-mediated reactions: the oxidative coupling of amines and the oxidation of benzylic CH bonds toward high-value pharmaceutical synthons. High conversions (up to 98%), selectivities (up to 99%), and recyclability are attained with very low metal loadings in the reaction. The synergistic effect of Cu(II) and Cu(I) is the essential part in the reaction mechanism. The developed strategy opens the door to a broad portfolio of other SACs via their coordination to various functional groups of graphene, as demonstrated by successful entrapment of FeIII/FeII single atoms to carboxy-graphene.
C3N5: A Low Bandgap Semiconductor Containing an Azo-linked Carbon Nitride Fra...Pawan Kumar
Modification of carbon nitride based polymeric 2D materials for tailoring their optical, electronic and chemical properties for various applications has gained significant interest. The present report demonstrates the synthesis of a novel modified carbon nitride framework with a remarkable 3:5 C:N stoichiometry (C3N5) and an electronic bandgap of 1.76 eV, by thermal deammoniation of the melem hydrazine precursor. Characterization revealed that in the C3N5 polymer, two s-heptazine units are bridged together with azo linkage, which constitutes an entirely new and different bonding fashion from g-C3N4 where three heptazine units are linked together with tertiary nitrogen. Extended conjugation due to overlap of azo nitrogens and increased electron density on heptazine nucleus due to the aromatic π network of heptazine units lead to an upward shift of the valence band maximum resulting in bandgap reduction down to 1.76 eV. XRD, He-ion imaging, HR-TEM, EELS, PL, fluorescence lifetime imaging, Raman, FTIR, TGA, KPFM, XPS, NMR and EPR clearly show that the properties of C3N5 are distinct from pristine carbon nitride (g-C3N4). When used as an electron transport layer (ETL) in MAPbBr3 based halide perovskite solar cells, C3N5 outperformed g-C3N4, in particular generating an open circuit photovoltage as high as 1.3 V, while C3N5 blended with MAxFA1–xPb(I0.85Br0.15)3 perovskite active layer achieved a photoconversion efficiency (PCE) up to 16.7%. C3N5 was also shown to be an effective visible light sensitizer for TiO2 photoanodes in photoelectrochemical water splitting. Because of its electron-rich character, the C3N5 material displayed instantaneous adsorption of methylene blue from aqueous solution reaching complete equilibrium within 10 min, which is significantly faster than pristine g-C3N4 and other carbon based materials. C3N5 coupled with plasmonic silver nanocubes promotes plasmon-exciton coinduced surface catalytic reactions reaching completion at much low laser intensity (1.0 mW) than g-C3N4, which showed sluggish performance even at high laser power (10.0 mW). The relatively narrow bandgap and 2D structure of C3N5 make it an interesting air-stable and temperature-resistant semiconductor for optoelectronic applications while its electron-rich character and intra sheet cavity make it an attractive supramolecular adsorbent for environmental applications.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
This work studied the effect of applying pulse current
(ton=off=1s) on the electrodeposition of silver nanoparticles on
carbon sphere surface as a substrate. The electrolyte is made of 0.1
M KNO3, 0.1 M KCN and 0.01M AgNO3. The pH value has been
adjusted in the alkaline region of 9.1 with the help of K(NO3)
addition. Experiments were carried out at room temperature for
periods up to 12 minutes. The cell is fitted with a mechanical stirrer
to keep the electrolyte in a dynamic state. Product(s) was
characterized with the help of SEM and EDX and field emission.
Results obtained show that silver nanoparticles has successfully
electrodeposited under pulse current conditions with a particle size
of 100–400 nm after 2 minutes. Deposition takes place on certain
accessible sites of the carbon surface of the substrate forming a
monolayer of scattered silver nanoparticles. Formation of macro
particles with larger diameter and multilayer in thickness takes
place with continuous deposition of silver nanoparticles on the
formerly deposited silver. Pulse current helps management of the
monolayer deposition as compared to the steady DC application
with respect to particle diameter and number of layers.
Photocatalytic Mechanism Control and Study of Carrier Dynamics in CdS@C3N5 Co...Pawan Kumar
We present a potential solution to the problem of extraction of photogenerated holes from CdS nanocrystals and nanowires. The nanosheet form of C3N5 is a low-band-gap (Eg = 2.03 eV), azo-linked graphenic carbon nitride framework formed by the polymerization of melem hydrazine (MHP). C3N5 nanosheets were either wrapped around CdS nanorods (NRs) following the synthesis of pristine chalcogenide or intercalated among them by an in situ synthesis protocol to form two kinds of heterostructures, CdS-MHP and CdS-MHPINS, respectively. CdS-MHP improved the photocatalytic degradation rate of 4-nitrophenol by nearly an order of magnitude in comparison to bare CdS NRs. CdS-MHP also enhanced the sunlight-driven photocatalytic activity of bare CdS NWs for the decolorization of rhodamine B (RhB) by a remarkable 300% through the improved extraction and utilization of photogenerated holes due to surface passivation. More interestingly, CdS-MHP provided reaction pathway control over RhB degradation. In the absence of scavengers, CdS-MHP degraded RhB through the N-deethylation pathway. When either hole scavenger or electron scavenger was added to the RhB solution, the photocatalytic activity of CdS-MHP remained mostly unchanged, while the degradation mechanism shifted to the chromophore cleavage (cycloreversion) pathway. We investigated the optoelectronic properties of CdS-C3N5 heterojunctions using density functional theory (DFT) simulations, finite difference time domain (FDTD) simulations, time-resolved terahertz spectroscopy (TRTS), and photoconductivity measurements. TRTS indicated high carrier mobilities >450 cm2 V–1 s–1 and carrier relaxation times >60 ps for CdS-MHP, while CdS-MHPINS exhibited much lower mobilities <150 cm2 V–1 s–1 and short carrier relaxation times <20 ps. Hysteresis in the photoconductive J–V characteristics of CdS NWs disappeared in CdS-MHP, confirming surface passivation. Dispersion-corrected DFT simulations indicated a delocalized HOMO and a LUMO localized on C3N5 in CdS-MHP. C3N5, with its extended π-conjugation and low band gap, can function as a shuttle to extract carriers and excitons in nanostructured heterojunctions, and enhance performance in optoelectronic devices. Our results demonstrate how carrier dynamics in core–shell heterostructures can be manipulated to achieve control over the reaction mechanism in photocatalysis.
A Front Surface Optimization Study for Photovoltaic ApplicationTELKOMNIKA JOURNAL
In this paper, we presented a possible front surface optical enhancement of Si solar cell by
optimizing the Antireflection (AR) and light trapping (LT) schemes. Conventional plasma enhanced
chemical vapor deposition (PECVD) and in house hot wire chemical vapor deposition (HWCVD) tool was
used to deposit Silicon Nitride (SiNX) layer and optimized at 668nm wavelength. This was followed by
surface texturing of random pyramids to further enhance the broadband reflectance of the front surface.
Broadband reflectance measurement using integrating sphere method showed achieved weighted average
reflectance (WAR) value of as low as 1.8% and 1.5%, when 85nm SiNX was deposited on top of random
pyramids structure using HWCVD and PECVD methods, respectively.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Dielectric properties of Ni-Al nano ferrites synthesized by citrate gel methodIJERA Editor
Ni–Al ferrite with composition of NiAlxFe2-xO4 (x=0.2, 0.4 0.6, and 0.8, ) were prepared by citrate gel method. The Dielectric Properties for all the samples were investigated at room temperature as a function of frequency. The Dielectric constant shows dispersion in the lower frequency region and remains almost constant at higher frequencies. The frequency dependence of dielectric loss tangent (tanδ) is found to be abnormal, giving a peak at certain frequency for mixed Ni-Al ferrites. A qualitative explanation is given for the composition and frequency dependence of the dielectric loss tangent.
Dielectric properties of Ni-Al nano ferrites synthesized by citrate gel methodIJERA Editor
Ni–Al ferrite with composition of NiAlxFe2-xO4 (x=0.2, 0.4 0.6, and 0.8, ) were prepared by citrate gel method. The Dielectric Properties for all the samples were investigated at room temperature as a function of frequency. The Dielectric constant shows dispersion in the lower frequency region and remains almost constant at higher frequencies. The frequency dependence of dielectric loss tangent (tanδ) is found to be abnormal, giving a peak at certain frequency for mixed Ni-Al ferrites. A qualitative explanation is given for the composition and frequency dependence of the dielectric loss tangent.
This to demonstrate the laser ablation of hard materials to form a thin film for optical sensors. The work was done at DIllard University , New Orleans LA by Professor Abdalla Darwish. any comment e-mail adarwish@bellsouth.net.
Raman investigation of femtosecond laser-induced graphitic columns in single-...PROMETHEUS Energy
We report on the fabrication of graphitic columns
induced in single-crystal diamond plates using 100 fs
laser pulses at 800 nm wavelength. Different values of
laser fluence (0.6–1.2 J/cm2
) and graphitization speed
(1–100 lm/s) were used for the laser treatment. A Raman
investigation was performed aimed at evaluating the
structural properties of the fabricated columns, showing
that a lower laser fluence and a proper choice of graphitization
speed may improve the degree of graphite crystallinity,
and suppress the residual diamond content.
IMPROVEMENT IN MORPHOLOGICAL AND ELECTRO-MAGNETIC BEHAVIOUR OF HARD FERRITE P...Editor IJMTER
The Ni-Ir substituted strontium ferrite of Sr(Ni-Ir)xFe12-2xO19 (x = 0.02 & 0.08) were
synthesized by sol-gel auto combustion technique and characterized using X-ray diffraction (XRD),
Transmission Electron Microscopy (TEM) for morphological behaviour with electrical
characteristics using Impedance Analyzer. XRD results confirmed the formation of a single phase
M-type hexagonal unit cell of space group P63/mmc. The increase in Ni-Ir concentration increases
the lattice parameter. TEM analysis of the sample demonstrates the formation of nano-size particles
which decreases with substitution. In this paper we reported the variation of dielectric constant,
dielectric loss, tangent loss, conductivity and magnetic behaviour with composition with temperature
and frequency analysis of the sample. The migration of Fe3+ ion from octahedral to tetrahedral site
decreases the dielectric constant with increase in Ni-Ir concentration. Activation energies were
found similar with calculated at ferromagnetic and paramagnetic region. The material study we
confined that the activation energy in the paramagnetic region is higher than that in the
ferromagnetic region. The enhanced resistivity of Ni-Ir substituted strontium hexaferrites is a
prospective application in high frequency and in microwave devices development.
Optical and Impedance Spectroscopy Study of ZnS NanoparticlesIJMER
International Journal of Modern Engineering Research (IJMER) is Peer reviewed, online Journal. It serves as an international archival forum of scholarly research related to engineering and science education.
International Journal of Modern Engineering Research (IJMER) covers all the fields of engineering and science: Electrical Engineering, Mechanical Engineering, Civil Engineering, Chemical Engineering, Computer Engineering, Agricultural Engineering, Aerospace Engineering, Thermodynamics, Structural Engineering, Control Engineering, Robotics, Mechatronics, Fluid Mechanics, Nanotechnology, Simulators, Web-based Learning, Remote Laboratories, Engineering Design Methods, Education Research, Students' Satisfaction and Motivation, Global Projects, and Assessment…. And many more.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Preparation, Structure, and Characterization of Nd2mo2o9 fast Oxide Ion Condu...IJARIIT
The structure and ion conductivity of Nd2Mo2O9powders were synthesized by using Nd(NO2)3, MoO3, and aspartic acid (fuel) in assisted combustion method with heating at 550˚C for 6 hours. The thermal decomposition, phase identification, morphology, ionic conductivity of the samples were studied by TGA/DTA, XRD and SEM four probe D.C. method respectively. The formation of Nd2Mo2O9 was confirmed by FTIR studies. The synthesis and crystallization were followed by thermochemical techniques (TGA/DTA) studies. The synthesized materials showed reasonable ionic conductivity. These results indicate that assisted combustion method is a promising method to prepare nanocrystalline Nd2Mo2O9 for solid oxide fuel cell.
Effect of Sn Doping on Structural and Electrical Properties of ZnO Thin Films...journal ijrtem
Abstract: Un-doped and tin (Sn) doped ZnO films were deposited on heated glass substrates by chemical spray pyrolysis method
(CSP). The effect of Sn concentration on the structural, surface morphological and electrical properties of the SnO2 films was
investigated. XRD analyses showed that the obtained films are polycrystalline in nature with hexagonal structure with preferred
orientation of (101). Doping with tin (Sn) causes increase in the grain size. Atomic force microscopy images showed that the root
mean square of the average surface roughness's varied from (1.48 to 3.58) as dopant concentration increased from 0 to 5 wt.%. The
electrical properties of the Sn ZnO films were strongly influenced by doping concentration. The electrical resistance of the films was
sharply decreased as dopant concentration increased.
Keywords: (ZnO) thin films, Sn Doping, Structural and electrical Properties
In this research, we propose a novel recommendation for improving CCT-D and lumen output (LO) of the 6600K in-cup packaging white LEDs (ICP-WLEDs) by varying its particle concentration. By using Light Tools and Mat lab software based on the Mie Theory, we derive the influence of the red phosphor particle’s concentration on the D-CCT and LO. The results show that the CCT-D are significantly affected when the concentration of the red phosphor varying from 0% to 1.8%. The CCT-D decreases from 4000K to 2200K and LO increases from 800 lm to 1300 lm.
Crystal Growth and Studies of Dihydrogen Phosphates of Potassium and Ammonium...IJERA Editor
A nonlinear optical (NLO) material Potassium dihydrogen phosphates (KDP) and Ammonium dihydrogen
phosphates (ADP) are grown by slow evaporation solution growth technique. The FTIR studies confirm the
presence of the functional group in the grown crystal. The optical transmittance studies show that the crystal has
transparence in the entire visible and IR region. The thermal stability of the materials was assessed by TG/DTA
analysis. The mechanical stability of the grown crystals was analyzed by Vicker’s microhardness test. The
dielectric behavior of the crystals was tested by dielectric analysis. The second harmonic generation (SHG) of
KDP is confirmed by Kurtz and Perry powder technique using Nd: YAG laser.
Crystal Growth and Studies of Dihydrogen Phosphates of Potassium and Ammonium...IJERA Editor
A nonlinear optical (NLO) material Potassium dihydrogen phosphates (KDP) and Ammonium dihydrogen
phosphates (ADP) are grown by slow evaporation solution growth technique. The FTIR studies confirm the
presence of the functional group in the grown crystal. The optical transmittance studies show that the crystal has
transparence in the entire visible and IR region. The thermal stability of the materials was assessed by TG/DTA
analysis. The mechanical stability of the grown crystals was analyzed by Vicker’s microhardness test. The
dielectric behavior of the crystals was tested by dielectric analysis. The second harmonic generation (SHG) of
KDP is confirmed by Kurtz and Perry powder technique using Nd: YAG laser.
Optical characterization of Se90S10-xCdx thin filmsIOSR Journals
Thin films of different thicknesses of Se90S10-xCdx, (x=0 and 5) were deposited by thermal evaporation technique onto glass substrates. X-ray diffraction patterns (XRD), differential thermal analysis (DTA) and energy dispersive X-ray spectroscopy (EDX) studies were carried out for samples in powder and thin film forms. XRD indicates that all the deposited thin films have an amorphous structure. The transmittance at normal incidence for these films was measured in the wavelength range 350–2500 nm. Applying Swanepoel's method successfully enabled to determine, with high accuracy, the film thickness, the real index of refraction and imaginary part of index of refraction. Regarding the optical absorption measurements; the type of optical transition and optical band gap were estimated as a function of photon energy. The effect of Cd addition on the refractive index, absorption coefficient and the optical band gap were investigated. The high frequency dielectric constant, the single oscillator energy, the dispersion energy and refractive index dispersion parameter were evaluated. Solar cell criterions have been considered. The results are interpreted in terms of concentration of localized states.
2. splitting between fundamental and excited state levels. Finally but not the least, suitable
thermal conductivity and moderate splitting on energy level 4
F3/2 are advantageous.
Laser operations based on transition 4
F3/2→4
I9/2 of Nd3+
ions have been investigated in
aluminum hosts [3–5]. In this letter, we report a diode pumped laser operation at 914 nm in
monoclinic silicate family of neodymium doped scandium silicate (Nd:Sc2SiO5, Nd:SSO)
crystal.
2. Gain cross section on energy transition 4
F3/2→4
I9/2 of Nd3+
ions in Nd:SSO crystal
1 at.% Nd:SSO single crystal was grown by Czochralski technique. The orientation of the
crystal used for the absorption and emission spectra measurement is b-cut sample parallel to
Y axis where b represents for crystallographic axis and Y represents for optical indicatrix
axis. Branching ratio for energy transition 4
F3/2→4
I9/2 of Nd3+
ions with central wavelength at
914 nm was calculated to be 30% by Judd-Ofelt theory [6]. The room temperature absorption
spectra were carefully measured with light changeover at 861 nm in order to get rid of
covering the band signals of the related energy transfer. The absorption cross section σabs and
emission cross section σem is shown in Fig. 1. The absorption cross section σabs at 803 nm was
calculated to be 1.69 × 10−20
cm2
and that at 808 nm was calculated to be 0.95 × 10−20
cm2
.
The stimulated emission cross section σem at 914 nm was estimated to be 1.13 × 10−20
cm2
by
using the Füchtbauer-Ladenburg equation [6].
Fig. 1. Room-temperature absorption and emission cross section in Nd:SSO crystal.
Gain cross section, denoted as σg and measured in units of area, is an important parameter
in a laser design and operation. σg determines the transition populations from the upper levels
to lower levels caused by a particular flux of photons. σg can be estimated with spectroscopic
measurements and fluorescence lifetime. The gain cross section could be given by Eq. (1) [7].
(1 )g em absσ β σ β σ= × − − × (1)
It can be noted that β is the inversion coefficient defined as the population ratio on 4
F3/2
level over the total Nd3+
ion population densities. Figure 2 shows the gain cross section σg
around 914 nm obtained for different inversion ratio β. For β = 1, gain cross-section σg is
equal to the emission cross section σem. It can be indicated from Fig. 2 that laser inversion at
914 nm may happen at β = 0.25 with obtained σg of 1.42 × 10−21
cm2
.
#199523 - $15.00 USD Received 15 Oct 2013; revised 12 Jan 2014; accepted 13 Jan 2014; published 14 Feb 2014
(C) 2014 OSA 1 February 2014 | Vol. 4, No. 2 | DOI:10.1364/OME.4.000458 | OPTICAL MATERIALS EXPRESS 459
3. Fig. 2. Gain cross section of energy transition 4
F3/2→4
I9/2 in Nd:SSO crystal.
3. Spectroscopic parameters of energy transition 4
F3/2→4
I9/2 of Nd3+
in Nd:SSO crystal
Laser performance at 900 nm has been reported in Nd doped Sr1-xLaxMgxAl12-xO19 (Nd:ASL)
crystal due to the favorable spectroscopic parameters [3]. Laser operation at 946 nm in
Nd:YAG core ceramics composites has recently been realized [8]. Frequency doubling blue
laser based on the transition 4
F3/2→4
I9/2 of Nd3+
ions has been demonstrated in Nd:ASL crystal
and Nd:YAG ceramics [1,8]. Infrared laser emission based on energy transition 4
F3/2→4
I9/2 of
Nd3+
ions in SSO crystal was performed. Accordingly, the spectroscopic parameters in
Nd:SSO crystal are compared with those in Nd:ASL crystal and Nd:YAG ceramics as shown
in Table 1.
Table 1. Spectroscopic parameters of energy transition 4
F3/2→4
I9/2 of Nd ions in Nd:SSO
crystal and Nd:ASL crystal, Nd:YAG ceramics.
Host
X =
Ω4/Ω6
β 4
F3/2→4
I9/2
ΔE
cm−1
Thermal
Conductivity
W·m−1
·K−14
I9/2
4
I11/2
τexp
(μs)
σem ×
10−20
cm2
τexp × σem
(μs ×
10−20
cm2
)
Nd:SSO crystal [6]
0.3 0.30 0.57 215 1.16 249 526 4.1
Nd:ASL crystal [3]
0.95 0.45 0.45 380 0.23 87 553 4.4(c); 6.3(a)
Nd:YAG
ceramics [9–11] 0.67 0.37 0.51 250 9.32 2330 851 9
As shown in Table 1, the energy Stark splitting in Nd:SSO crystal is 526 cm−1
and the
value of τexp × σem is 2.49 × 10−18
μs·cm2
. The value of energy Stark splitting in Nd:ASL
crystal is 553 cm−1
but the value of τexp × σem is 8.7 × 10−19
μs.cm2
which is lower than that in
Nd:SSO crystal. The energy Stark splitting in Nd:YAG ceramic is the largest (851 cm−1
)
while the value of τexp × σem (2.33 × 10−17
μs.cm2
) is the largest [9,10]. Nd:SSO crystal
possess moderate value of τexp × σem when compared with those in Nd:ASL crystal and
Nd:YAG ceramic, while the energy splitting is close to that in Nd:ASL crystal. Taking
thermal property into account, SSO crystal possess the advantage of minus thermal-optics
coefficient (dn/dT = −6.3 × 10−6
K−1
) which is beneficial for releasing thermal lens effect [12].
With the favorable thermal conductivity (4.1 W·m−1
·K−1
) and moderate splitting (526 cm−1
) in
Nd:SSO crystal, efficient laser performance on energy transition 4
F3/2→4
I9/2 of Nd3+
ions in
SSO crystal can be expected.
#199523 - $15.00 USD Received 15 Oct 2013; revised 12 Jan 2014; accepted 13 Jan 2014; published 14 Feb 2014
(C) 2014 OSA 1 February 2014 | Vol. 4, No. 2 | DOI:10.1364/OME.4.000458 | OPTICAL MATERIALS EXPRESS 460
4. 4. Laser operation at 914 nm in Nd:SSO crystal
Laser setup for energy transition 4
F3/2→4
I9/2 in Nd:SSO crystal is shown in Fig. 3. Fiber
coupled laser diode (LIMO) with a numerical aperture of 0.22 and core diameter of 100 μm
was used as pump source with maximum output power of 35 W, where central emitting
wavelength could be tuned by a temperature controller. The coupling optics consists of two
identical plano - convex lenses with focal lengths of 100 mm used to reimage the pump beam
into the laser crystal at a ratio of 1:1. The resonator was consisted of an input coupler M1
(plane), Nd:SSO crystal and output coupler M2 (BK7). M1 is coated with HT @ 800 nm -
810 nm & 1083 nm and HR @ 914 nm. M2 is coated with HR @ 800 nm - 810 nm & Toc =
2.5% @ 914 nm with radius curvature of 100 mm. 1.0 at.% Nd:SSO sample with aperture of 5
mm × 5 mm and length of 10 mm was polished. The orientation of the polished crystal is b-
cut. The propagation of the light is along b direction. Filter RG850 (SHOTT company) was
used to cut the pump power left after the laser crystal. To further remove the generated heat
during laser oscillation, the Nd:SSO crystal was wrapped with indium foil and mounted in a
water-cooled copper heat sink. Temperature was controlled at 5 °C using a thermo-coupler
device.
Fig. 3. Laser setup for transition 4
F3/2→4
I9/2 in Nd:SSO crystal.
Fig. 4. Laser performance at 1083 nm in Nd:SSO crystal with different TOC.
Before moving to laser operation at 914 nm in Nd:SSO crystal, laser behavior at 1083 nm
on the 4
F3/2 → 4
I11/2 transition were recorded with different transparency of output coupler TOC
= 2%, TOC = 6% and TOC = 10% as shown in Fig. 4. The cavity mirrors were replaced with
coatings covering 1083nm accordingly. The highest output power of 2.54 W and slope
efficiency of 33.3% was obtained with TOC = 10% and absorbed pump power of 11.69W. In
the case of TOC = 6% and TOC = 2%, output power of 482 mW and 266 mW was obtained.
According to the absorption spectra shown in Fig. 1, the absorption band was centered at
811 nm and 803 nm. The commercially available laser diode pump with central wavelength of
#199523 - $15.00 USD Received 15 Oct 2013; revised 12 Jan 2014; accepted 13 Jan 2014; published 14 Feb 2014
(C) 2014 OSA 1 February 2014 | Vol. 4, No. 2 | DOI:10.1364/OME.4.000458 | OPTICAL MATERIALS EXPRESS 461
5. 808 nm was adopted. Unfortunately, the maximum pumping wavelength could not go further
to 811nm even with temperature adjustment. A second laser diode pump source with central
wavelength of 804 nm was employed. With the temperature adjustment on the laser diode
pump source, the best laser performance at 914 nm was obtained when the laser diode
emitting wavelength was centered at 803 nm. In the following discussion, Nd:SSO laser
pumped by different laser diode pump was compared with central wavelength of 803 nm and
808 nm.
The stable oscillation was maintained at cavity length of 11 cm. The relationships between
output power at 914 nm in Nd:SSO crystal and the absorbed pump power at 803 nm and 808
nm are shown in Fig. 5. The laser beam profile at 914 nm is also shown in Fig. 5. When laser
diode pump is centered at 803 nm, 271 mW of output power with 11.9 W of absorbed pump
power corresponding to a slope efficiency of 5.4% was obtained. On the other hand, the use of
laser diode pump centered at 808 nm led to 581 mW of output power with 13.3 W of absorbed
pump power, while the slope efficiency was found to be 8.6%. Laser diode pump source with
central wavelength of 808 nm is beneficial for higher laser output when compared to that of
803 nm, although the absorption cross section at 808 nm is lower than that at 803 nm
according to Fig. 1. The slope efficiency of 8.6% obtained could be affected by crystal
quality, crystal length, as well as the cavity conditions. Higher output power and slope
efficiency based on transitions of 4
F3/2→4
I9/2 of Nd ions could be expected by shortening
sample length, improving crystal quality and laser diode pump source with central wavelength
of 811 nm. These experiments are now under progress. Tracking back to the data in Table 1,
hosts with branch ratio higher than 30% for energy transition 4
F3/2→4
I9/2 of Nd ions seems to
be positive for laser performance.
Fig. 5. Laser operation at 914 nm in Nd:SSO crystal by laser diode pump centered at 803 nm
and 808 nm.
5. Conclusion
In conclusion, Nd:SSO with the advantage of minus refractive index versus temperature,
favorable thermal conductivity (4.1 W·m−1
·K−1
), moderate energy Stark splitting (526 cm−1
)
were firstly reported with laser performance at 914 nm. The realization of diode pumped laser
operation at 914 nm in monoclinic Nd:SSO crystal opens the way to prolific hosts for second
harmonic generation of blue lasers. Improvement of the optical quality of the Nd:SSO crystal
should help enhance the laser performances at 914 nm. This work is now in progress.
#199523 - $15.00 USD Received 15 Oct 2013; revised 12 Jan 2014; accepted 13 Jan 2014; published 14 Feb 2014
(C) 2014 OSA 1 February 2014 | Vol. 4, No. 2 | DOI:10.1364/OME.4.000458 | OPTICAL MATERIALS EXPRESS 462
6. Acknowledgments
We are grateful to the financial supports from Shanghai Municipal Natural Science
Foundation (Grant No. 13ZR1446100, 12JC1409100) and National Natural Science
Foundation of China (Grant No. 91222112, 61205171, 51272264).
#199523 - $15.00 USD Received 15 Oct 2013; revised 12 Jan 2014; accepted 13 Jan 2014; published 14 Feb 2014
(C) 2014 OSA 1 February 2014 | Vol. 4, No. 2 | DOI:10.1364/OME.4.000458 | OPTICAL MATERIALS EXPRESS 463