Optical temperature sensing is widely realized by using upconversion(UC) emission in lanthanide-doped phosphors. There are various parameters that are responsiblefor UC intensity of the phosphor like particle shape and size, type of symmetry that exist at the site position, distribution of lanthanide ions in the phosphor, and so on. However, a comparative study of the bulk and nanostructure on the temperature sensing ability of such phosphor is rare. In the presentwork,we have taken Ca0.79Er0.01Yb0.2MoO4 phosphors as amodel system and synthesized its bulk (via solid-state reactionmethod, named SCEY) and nanostructures(via solution combustion route, named CCEY).Wefurther studied their phase, crystal structure, phononfrequency, optical excitation, and emission(upconversion& downshifting) properties. Finally, the optical temperature sensing behavior of SCEY and CCEY, in the range 305 K–573 K, have been compared. Themaximum relative sensitivity of the phosphor SCEY and CCEY are 0.0061 K−1 at 305 K and 0.0094 K−1 at 299 K, respectively,while, themaximum absolute sensitivities are 0.0150 K−1 at 348 K, and 0.0170 K−1 at 398 K, respectively.We thus conclude that the temperature sensing ability of nanoparticlebased Ca0.79Er0.01Yb0.2MoO4phosphor is better compared to its bulk phosphor.

1. Temperature Sensing using Bulk and Nanoparticles of
Ca0.79Er0.01Yb0.2MoO4 phosphor.
Thesis Supervisor:
Dr. Sunil Kumar Singh
Assistant Professor
Department of Physics
I.I.T. (B.H.U.)
High End Workshop on “ Scattering Methods (Electron, X-ray and Ion beam) for Material
Characterization @IIT BBS
June 13-20, 2022
By: Sachin Singh
Roll No. :19171026
Ph.D. Inspire Fellow [IF180856]
Department of Physics
I.I.T. (B.H.U.)

2. Accomplished work to date
1. Temperature Sensing using Bulk and Nanoparticles of Ca0.79Er0.01Yb0.2MoO4
phosphor. (Under revision in the journal Methods and Applications in Fluorescence)
2. Effect of doping Bi3+ in Ca0.79Er0.01Yb0.2MoO4 phosphor for fluorescence study
and temperature sensor application. ( Synthesis, XRD, SEM, PL, and UC done.)

3. OUTLINE
1. Motivation
2. Project I. i.e. Ca0.79Er0.01Yb0.2MoO4
i. Synthesis
ii. Characterization & Analysis
iii. Conclusion
3. Future Plan

4. Motivation
HOST
Low phonon energy
Optically inert
High chemical and
thermal stability
SENSITIZER Large absorption
Cross-section
ACTIVATOR
Long lived
intermediate
energy states
(600cm-1)
(9*10-11cm-2)

5. Fig 1:energy level diagram of lanthanides
Rich ladder like energy levels(due to
splitting of 4f energy levels)
long lived energy states(metastable
states) due to 4f-4f parity forbidden
transition
Less sensitive to environment of host
(shielding of partially filled 4f electrons by
completely filled 5s25p6 subshells)
E.C = [Xe]4f0-145d0-16s2
LANTHANIDES -
unique optical
properties of
lanthanide doped
materials ???
Dual mode emission(downconversion and upconversion)
Sharp emission band
Stable oxidation state=+3

6. Temperature Sensing using Bulk and
Nanoparticles of Ca0.79Er0.01Yb0.2MoO4
phosphor.

7. Synthesis of CaMoO4 and Ca0.79Er0.01Yb0.2MoO4 (Bulk)using Solid State Reaction method
26.23 mol % CaO+ 52.53 mol % MoO3 + 1.0 mol % Er2O3 +20 mole % of Yb2O3
1 mol CaO+2 mol MoO3
Intermixed and intermediate grinding for 1 hour
Calcination performed at 1200 0C for 3 hours
Intermixed and intermediate grinding for 1 hour
Calcination performed at 1200 0C for 3 hours
Synthesis of CaMoO4 Synthesis of CaMoO4 :Er:Yb
• Formulae used for sample preparation :- Weight of raw material (in gm)
𝑤 =
𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑟𝑎𝑤 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙
𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑓𝑖𝑛𝑎𝑙 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑
×
[ 𝑛𝑜. 𝑜𝑓 𝑎𝑡𝑜𝑚𝑠 𝑖𝑛 𝑓𝑖𝑛𝑎𝑙 𝑝𝑟𝑜𝑑𝑢𝑐𝑡 ] × (𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑓𝑖𝑛𝑎𝑙 𝑝𝑟𝑜𝑑𝑢𝑐𝑡)(𝑖𝑛 𝑔𝑚)
[𝑛𝑜. 𝑜𝑓 𝑎𝑡𝑜𝑚𝑠 𝑖𝑛 𝑟𝑎𝑤 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙]
• Stoichiometric ratio:-
0.01Er2O3 + 0.2Yb2O3 +0.268CaO + 0.526(2MoO3) → Ca0.79Er0.01Yb0.2MoO4 + 5O2

8. Synthesis of Ca0.79Er0.01Yb0.2MoO4 (Nano) using sol-gel combustion
method
Figure 2: Schematic diagram of sol-gel method of UCNP synthesis

9. X-ray diffraction and TEM/SEM measurement: Phase and structure analysis
Figure 3. TEM image of (a) SCEY, (b) CCEY sample.
Elemental mapping of (c) SCEY, (d) CCEY sample.
Figure 4. (a) Rietveld refined XRD pattern of SCM sample
using the FullProf program, (b) XRD pattern of CCEY sample,
(c) XRD pattern of SCEY sample, (d) XRD Pattern of SCM
sample.

10. FTIRand Raman measurements: Vibrations and lattice phonon frequency analysis
Figure 5 : Fourier transforms infrared spectrum for (a) SCM,
(b) SCEY, and (c) CCEY.
Figure 6 : Raman spectra of CaMoO4 powder sample
synthesized by solid state reaction method.

11. UV-Visible absorption measurements: Bandgap calculation
Figure 7: UV-visible absorption spectra of (a) SCM (b) SCEY and (c) CCEY samples. Insets to the corresponding spectrum
shows the Tauc plot for the band gap calculation.

12. Luminescence studies:
Photo-luminescence excitation and emission
Figure 8: (a) excitation spectra, and (b) emission spectra of SCM, SCEY, and CCEY samples.

13. Experimental Setup for Upconversion Spectroscopy and Upconversion Spectra
Figure 9 . Experimental setup for
NIR to visible upconversion
spectroscopy.
Figure 10. (a) UC luminescence spectra of SCEY under different excitation power of 980
nm laser. (b) UC spectra of Er3+/ Yb3+ co-doped CaMoO4 synthesized by solid-state
reaction and gel-combustion method (10X). (c) Log-log plot of UC intensity vs. 980 nm
laser power of SCEY. (d) Log-log plot of UC intensity vs. 980 nm laser power of CCEY

14. Energy Level diagram of Er3+-Yb3+
Figure 11: Energy level diagram of the Yb3+, Er3+ ions and the proposed UC
mechanism in Er3+/ Yb3+ co-doped CaMoO4.

15. Temperature-dependent up-conversion: Optical temperature sensing
application
Figure 12: (a) Green emission FIR (I531/I553) vs. temperature plot, (b) the ln FIR (I531/I553) vs. inverse absolute temperature plot
of Er0.01Yb0.2Ca0.79MoO4 synthesized by the solid-state method (the UC spectra of the green band at 348 K and 498 K are shown
in inset). (c) The plot of relative sensitivity and absolute sensitivity as a function of the temperature of Er0.01Yb0.2Ca0.79MoO4
synthesized by the solid-state method.

16. Figure 13: (a) Green emission FIR (I531/I553) vs. temperature plot, (b) the ln FIR (I531/I553) vs. inverse absolute temperature plot
of Er0.01Yb0.2Ca0.79MoO4 synthesized by the gel-combustion method (the UC spectra of the green band at 348 K and 498 K are
shown in inset). (c) The plot of relative sensitivity and absolute sensitivity as a function of the temperature of
Er0.01Yb0.2Ca0.79MoO4 synthesized by the gel-combustion method.
𝑆𝑟 =
1
𝐹𝐼𝑅
×
)
𝜕(𝐹𝐼𝑅
𝜕𝑇
=
∆𝐸
𝑘𝐵𝑇2
𝑆𝑎 =
)
𝜕(𝐹𝐼𝑅
𝜕𝑇
= 𝐹𝐼𝑅 ×
∆𝐸
𝑘𝐵𝑇2

17. The crystal structure of the synthesized powder sample CaMoO4 is
tetragonal with space group I41/a.
 Band gap of SCM, SCEY and CCEY are 2.40 eV, 2.90 eV and 3.50 eV
respectively.
Emission intensity of Nano-particles has thirty times higher than
that of bulk one.
 (Bulk) Sr =0.0061 K-1 at 305 K, (Nano) Sr =0.0094 K-1 at 299 K.
(Bulk) Sa =0.0150 K-1 at 348 K, (Nano) Sr =0.0170 K-1 at 398 K.
 The sensitivity of CCEY is higher than the SCEY phosphor.
Conclusions+

18. Future Plan
• Preparation of NaYF4 doped with Er3+, Ho3+ and Tm3+ and Yb3+ ions
(upconverter).
• Functionalization of Phosphors with Infrared Dyes (for conversion
of IR part of Sunlight to visible region using incoherent light source)
• Design of state-of-art photovoltaic device coated with functionalized
phosphor and test the improvement in Photovoltaic parameters.

19. References
i. Guler U, Sendi M.S.E, Ghovanloo, M, ``dual-mode passive rectifier for wide-range input power flow, IEEE
60th International Midwest Symposium on Circuits and Systems (MWSCAS), Aug. 2017.
ii. Chae, Seung Yong; Park, Myun Kyu; Lee, Sang Kyung; Kim, Taek Young; Kim, Sang Kyu; Lee, Wan In
(August 2003). "Preparation of Size-Controlled TiO 2 Nanoparticles and Derivation of Optically Transparent
Photocatalytic Films". Chemistry of Materials. 15 (17): 3326–3331.
iii. Y. Wang, K. Zheng, S. Song, D. Fan, H. Zhang, X. Liu, Remote manipulation of upconversion luminescence
Chem. Soc. Rev., 2018,47, 6473-6485 .
iv. A. Kar and A. Patra, Nanoscale, 2012, 4, 3608.
v. D. Timmerman, I.Izeddin, P. Stallinga, I. N. Yassievich and T. Gregorkiewicz, Nat. Photonics, 2008, 2, 105–
109.
vi. X.Chen, W.Xu,H. Song, C. Chen, H. Xia, Y. Zhu, D. Zhou, S. Cui, Q. Dai and J. Zhang, ACS Appl. Mater.
Interfaces,2016, 8, 9071–9079.
vii. Z. Fan, K. Sunc and J. Wang, J. Mater. Chem. A, 2015, 3,18809–18828.
viii. P Singh, PK Shahi, SK Singh*, et al, Nanoscale, 9, 696 (2017).

20. Thank You for Attention