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EMRS 2018 Replacing rare earth ions in LEDs (?)
The document discusses the critical role of rare earth elements (REE) in phosphor converted LEDs, which contribute to a significant portion of global electricity consumption. It addresses the need for alternatives to key phosphors like Eu3+ and Ce3+ and explores various materials and requirements for effective LED phosphors. Additionally, it highlights advancements in quantum dots as potential substitutes, while emphasizing the importance of phosphor recycling in the context of LED technology.
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EMRS 2018 Replacing rare earth ions in LEDs (?)
- 1. Are alternatives neededfor the workhorses Eu2+ and Ce3+ in phosphor converted LEDs? June 18 2018 http://LumiLab.UGent.be Philippe Smet philippe.smet@ugent.be @pfsmet EMRS Spring meeting – Strasbourg – 18 to 22 June 2018 @UGentLumiLab Presentation can be downloaded at http://www.slideshare.net/pfsmet
- 3. Lighting accounts foran estimated 18% of the world’s electricity consumption. Fluorescent and LED lighting use rare earth elements. The RE elements regularly make headlines. Do we really need RE for lighting?
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- 7. Luminous efficacy ofradiation (LER) – lumen/Watt V(λ) 400nm 700nm550nm
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- 11. Fluorescent lighting -principle Conversion by photoluminescent materials (hence “fluorescence lamps”)
- 12. Emission spectrum fluorescentlighting 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+) @pfsmet
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- 15. °1907 – SiC– yellow emission 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: predicted in GaN-based LEDs in 1950s! LEDs – direcht conversion of electricity into light
- 16. Nobel prize physics2014 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"
- 17. Light emitting diodes(LEDs) Nobel prize communication p n Direct bandgap needed! Nearly monochromatic light.
- 18. RGB LEDs –the green gap. Source: OSRAM (In,Ga)N (Al,Ga,In)P Green gap
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- 21. 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) Y3Al5O12:Ce yellow phosphor .new application ..new requirements ...new phosphors Phosphors for LEDs Blue LED
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- 23. Tunability of Eu2+based phosphors Phosphors for LEDs Journal of Luminescence (2003) 104, p. 239@pfsmet
- 24. Phosphors for LEDs Thousandsof 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...)
- 25. 6 (scientific) requirementsfor LED phosphors • Suitable emission spectrum (peak, width) • High (quantum) efficiency (QY, QE) • Strong absorption at +/- 460nm (EQE) • Chemically stable • Short luminescence lifetime • Thermal stability Phosphors for LEDs + cost, embedding,… ECS Journal of the Electrochemical Society (2011) 158, p. R37@pfsmet
- 26. ECS Journal ofthe Electrochemical Society (2011) 158, p. R37 Only handful of phosphors are suitable for high brightness LEDs. Two dopants: Ce3+ and Eu2+ 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
- 27. Nature Materials (2017)16, p. 500 (Thermal) losses for phosphor converted LEDs Assuming QE for phosphor of 90%, overall luminous efficacy 180 lum/W. @pfsmet
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- 29. Lab record –CREE 303 lum/watt IKEA PHILIPS NICHIA Luminous efficacy (LE) Fluorescent lighting threshold DoE
- 31. RE usage • Host:yttrium (YAG), dopants: cerium, europium. • Phosphors and pigments: 7% of RE usage (2013, Roskill) • Key applications (CRT displays, fluorescent (+ Tb3+)) + LEDs • On chip: very low phosphor quantities • In first order, phosphor use does not scale with luminance
- 32. • Narrow redphosphor 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
- 33. Red components: Eu2+doped http://dx.doi.org/10.1155/2014/290952 CaAlSiN3:Eu2+
- 34. Red Mn4+ dopedfluoride phosphors K2SiF6:Mn4+
- 36. Synthesis methods HF +KMnO4 @pfsmet
- 38. ECS Journal ofSolid State Science and Technology (2016) 5, p. R3040
- 39. Quantum dots asan alternative?
- 40. Colloidal Quantum Dots| what? ̶ 1983, first discovery in Bell Labs ̶ Since 1990’s, accelerated development Size-Tunable Optical Properties 5nm diameter wavelength produced as printable inks CdSe/CdS, InP/ZnSe, perovskites,…
- 41. Lowering synthesis costof InP QDs Aminophosphines – a new phosphorous precursor Song, J. Nanoparticle Res. 2013 Tessier, Chem. Mater. 2015 Kim, Angew. Chemie Int. Ed. 2016 Buffard, Chem. Mater. 2016 Full Green-to-red color range accessible
- 42. Samsung KS7500 “25% morecolour”
- 43. QDs for displays Colourfiltering: balance between color gamut and efficiency ߣ (nm) 350 450 550 650 transmission 100% Liquid crystal display Colour filters
- 44. Displays • (AM)OLEDs vsLED 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
- 45. General lighting • Furtherefficiency increase needed • Long lifetime required (>50 khrs) • Color quality after brightness increase • Blue LED flux strongly increased • Very competitive market Trends Displays Other applications
- 46. Conclusions • Phosphor convertedLEDs : relevant energy saving technology • RE – based phosphors are key elements (Y, Ce, Eu, Tb) • Mass to luminance ratio is decreasing • Some alternative materials available (red Mn4+ fluorides) • Display backlighting: competitive non-RE technologies • Phosphors: recycling is an issue!
- 47. Contact & resources PhilippeSmet philippe.smet@ugent.be @pfsmet http://LumiLab.UGent.be @UGentLumiLab Presentation can be downloaded at http://www.slideshare.net/pfsmet Looking forward to your feedback!