Are quantum dots superseding traditional phosphors in solid state lighting
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This document summarizes key topics in solid state lighting, including a brief history of lighting technologies and the development of LEDs. It discusses the use of phosphor converted LEDs and potential advantages of quantum dots for LEDs. The document outlines requirements for phosphors and quantum dots used in LEDs and notes ongoing research directions, such as developing more efficient red phosphors and quantum dots with stable color points.
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Are quantum dots superseding traditional phosphors in solid state lighting
- 1. Are quantum dots superseding traditional phosphors in solid state lighting? May 22 2017 http://LumiLab.UGent.be Philippe Smet philippe.smet@ugent.be @pfsmet Phonsi Summer School – Fréjus – 22 to 26 May 2017 @UGentLumiLab
- 2. Menu A brief history of lighting Key units and metrics in lighting Phosphor converted LEDs Quantum dots for LEDs
- 3. A quiz to get started! 0.0 0.2 0.4 0.6 0.8 1.0 350 450 550 650 750 Emission wavelength (nm) Intensity A: Sun LED Incandescent Fluorescent B: Sun LED Incandescent Fluorescent C: Sun LED Incandescent Fluorescent D: Sun LED Incandescent Fluorescent
- 7. Luminous efficacy of radiation (LER) – lumen/Watt V(l)Visible region: 380-780nm (450-650nm) Different after eye-surgery Different for animals Low light levels: rods (grey) High light levels: 3 types of cones (colour) 400nm 700nm550nm
- 13. Correlated colour temperature (CCT) CIE x,y colour diagram For every light source, colour coordinates (x,y) can be calculated CCT is temperature of closest black body radiator
- 14. Colour rendering (CRI) – colour quality
- 15. Colour rendering (CRI) – colour quality
- 16. High pressure mercury Colour rendering (CRI) – colour quality Light source being tested Black body with same CCT
- 17. Requirements for light sources (general lighting) • CCT: 2500 – 6500K Tunable • CRI (/100): as high as possible Accurate reproduction of colours • LER (lum/wattopt): as high as possible No photon waste outside eye sensitivity • LE (lum/wattelec): as high as possible Takes elec>opt conversion into account
- 20. Emission spectrum fluorescent lighting 0.0 0.2 0.4 0.6 0.8 1.0 350 450 550 650 750 Emission wavelength (nm) Intensity Tb3+ Tb3+ Eu3+ Hg 254nm (La,Ce)PO4:Tb3+ Y2O3:Eu3+ (BaMgAl10O17:Eu2+)
- 26. Light emitting diodes (LEDs) Nobel prize communication p n Direct bandgap needed! Nearly monochromatic light.
- 27. Nobel prize physics 2014 Isamu Akasaki Hiroshi Amano Shuji Nakamura "for the invention of efficient blue light-emitting diodes (LEDs) which has enabled bright and energy-saving white light sources"
- 28. RGB LEDs – the green gap. Source: OSRAM (In,Ga)N (Al,Ga,In)P Green gap
- 29. ECS Journal of the Electrochemical Society (2011) 158, p. R37 RGB LEDs for general lighting? Colour rendering LER (lum/watt) CCT =3000K B G R Fourth LED needed for high CRI Differential ageing T-dependent colour shifts Low efficiency of GR! G R
- 31. Colour rendering LER (lum/watt) B G R Nature Materials (2014) 13, p. 891 || ECS Journal of the Electrochemical Society (2011) 158, p. R37
- 32. Materials (2010) 3, 2834 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 400 500 600 700 Normalizedintensity Wavelength (nm) Blue LED Y3Al5O12:Ce yellow phosphor .new application ..new requirements ...new phosphors Phosphors for LEDs
- 33. Thousands of different phosphors can be made... Main luminescent ions Main host constituents Example: “YAG:Ce” = Y2.97Ce0.03Al5O12 Phosphors for LEDs
- 35. Tunability of Eu2+ based phosphors Phosphors for LEDs Journal of Luminescence (2003) 104, p. 239
- 36. Phosphors for LEDs Thousands of different phosphors can be made... ... but only a handful are actually used. • garnets (YAG:Ce, LuAG:Ce,...) • silicates ((Ca,Sr,Ba)2SiO4:Eu,...) • oxynitrides (SrSi2O2N2:Eu, SiAlONs,...) • nitrides ((Ba,Sr)2Si5N8:Eu, CaAlSiN3:Eu...)
- 37. 6 (scientific) requirements for LED phosphors • Suitable emission spectrum (peak, width) • High (quantum) efficiency (QY, QE) • Strong absorption at +/- 460nm (EQE) • Chemically stable • Short luminescence lifetime (no saturation) • Thermal stability Phosphors for LEDs + cost, embedding,… ECS Journal of the Electrochemical Society (2011) 158, p. R37
- 38. ECS Journal of the Electrochemical Society (2011) 158, p. R37 Only handful of phosphors are suitable for high brightness LEDs 6 (scientific) requirements for LED phosphors • Suitable emission spectrum (peak, width) • Strong absorption at +/- 460nm • High (quantum) efficiency • Chemically stable • Short luminescence lifetime (no saturation) • Thermal stability LED Heat sink Phosphor Phosphors for LEDs
- 39. Nature Materials (2017) 16, p. 500 (Thermal) losses for phosphor converted LEDs Assuming QE for phosphor of 90%, overall luminous efficacy 180 lum/W.
- 40. 0 20 40 60 80 100 250 350 450 550 650 750 Intensity (arb. units) Wavelength (nm) excitation emission λem = 630 nm λex = 455 nm K2SiF6:Mn4+ Mn4+ - New kid on the red-emitting phosphor block ECS Journal of Solid State Science and Technology (2016) 5, p. R3040
- 41. Mn4+ adds saturated & efficient red emission 0 1 2 3 4 5 400 500 600 700 Normalized intensity (a.u.) Wavelength (nm) + saturated red + boosts LER - long radiative lifetime - stability
- 44. Lab record – CREE 303 lum/watt IKEA PHILIPS NICHIA Luminous efficacy (LE) Fluorescent lighting threshold DoE
- 45. • Narrow red phosphor Chemically stable, thermally stable, with high saturation level. • Narrow banded cyan/green phosphors. • Phosphors for high brightness applications Headlights, projectors. • Improved thermal quenching (quantum deficit) • Rare earth free (?) Key issues in phosphor research
- 46. Where are the quantum dots???
- 47. Samsung KS7500 “25% more colour”
- 48. QDs for displays Colour filtering: balance between color gamut and efficiency 𝜆 (nm) 350 450 550 650 transmission 100% Liquid crystal display Colour filters
- 49. Colour gamut Colour, colours, colours!!!
- 50. • Suitable emission spectrum (peak, width) • Strong absorption at +/- 460nm • High (quantum) efficiency • Chemically stable • Short luminescence lifetime (no saturation) • Thermal stability 6 (scientific) requirements for QDs for LEDs QDs for LEDs + cost, embedding, Cd-free, stable color point… • Mix, size distribution • Core-shell structures, no reabsorption • When embedded! • Chemically stable (15-50khrs) • Linear response • Thermal quenching/degradation
- 51. Reducing excitation flux and temperature ECS Journal of Solid State Science and Technology (2013) 2, p. R3026
- 52. CdSe/CdS QDs SrGa2S4:Eu2+ Blue LED Merging both worlds Light: Science & Applications (2017) 6, p. e16271
- 53. Displays • (AM)OLEDs vs LED backlight Blue OLEDs degrade faster • Main drivers: colour gamut and efficiency • Quantum dots (Cd-free…) vs phosphors (Mn4+) • Electroluminescence from QDs (no filtering, printing,…) Trends
- 54. General lighting • Further efficiency increase needed • Color quality after brightness increase • Blue LED flux strongly increased • Very competitive market Trends Displays Other applications
- 55. Contact http://LumiLab.UGent.be Philippe Smet philippe.smet@ugent.be @pfsmet Thanks for listening! @UGentLumiLab
- 56. LED compact fluorescent incandescent (halogen) Fluorescent lighting – a transition technology
- 57. diameter 2 nm 4 nm 57 Sofie Abé, Iwan Moreels
- 58. History of LEDs °1907 – SiC – yellow emission (other colours at higher voltage) 1940s: theoretical framework (cfr. transistor, p-n junction) 1955: EL in III-V compounds 1962: IR emission in GaAs (+ laser) 1960s: green and red LEDs based on GaP Blue emission: predicted in GaN-based LEDs in 1950s! (p) doping interferes with crystal growth Nobel prize work: creating ideal growth conditions for GaN by seed layers + conditions to create p-doping
- 59. Projection – point sources display-central.com
- 60. LiFi
- 61. Variable emission colours Added value to lighting Controlled with smart phone (via WiFi bridge) Not fully RGB! Circadian rhythm
- 62. Smart textiles
- 63. Light source of the future! Future shape? Google images “LED lamp”
- 64. Light source of the future! Future shape? Google images “LED lamp” + design
- 65. Application: remote phosphors Phosphor LED Heat sink Remote phosphor Reflective cavity Lower phosphor temperature (...) Lower photon flux at phosphor level Freedom in design Optical management Phosphor cost + - Philips LEDmaster
Editor's Notes
- Aan te passen
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- The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×1012hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.
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- Edison. 1847-1931
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- GR since 1960s; wait until early 1990s for efficient blue LEDs.