Overview of lighting technologies. Focus on blue LEDs, solid state lighting, colour conversion by luminescent materials. Applications of LEDs. Future of lighting.

1. NB Photonics Summer School
The amazing rise of solid state lighting
August 24 2015
http://LumiLab.UGent.be
Philippe Smet
philippe.smet@ugent.be
@pfsmet

2. A quiz to get started!
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Emission wavelength (nm)
Intensity
A: Sun LED Incandescent Fluorescent
B: Sun LED Incandescent Fluorescent
C: Sun LED Incandescent Fluorescent
D: Sun LED Incandescent Fluorescent

3. A brief history of lighting

4. Lighting technologies

5. Lighting technologies
° 1802 – Humphry Davy
battery + Pt wire
° 1878 – Thomas Edison
carbonized bamboo filament

6. Lighting technologies
lumen per Watt

7. Luminous efficacy of radiation (LER) – lumen/Watt
V(l)
93 lm/W

8. Correlated colour temperature (CCT)
CIE x,y colour diagram

9. Lighting technologies
15 lm/W

10. Lighting technologies
Mercury, 254nm (UV-C)

11. Lighting technologies
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Tb3+
Tb3+
Eu3+
Hg
254nm
(La,Ce)PO4:Tb3+
Y2O3:Eu3+
(BaMgAl10O17:Eu2+)

12. Luminescence
‘Cold light’: generation of light in a non-thermal way
• Photoluminescence (PL)
• Cathodoluminescence (CL)
• Electroluminescence (EL)
• Chemoluminescence
• Bioluminescence
• Radioluminescence (RL)
• Triboluminescence
• Sonoluminescence
Organic luminescent materials
Inorganic luminescent materials (= phosphors)

13. Luminescence
Credits: Samsung, Philips, TU Delft, Wikimedia, Highdisplay

14. LED
compact fluorescent
incandescent (halogen)
Pro/con of fluorescent lighting
Efficiency limit in fluorescent tubes: Stokes losses!

15. Colour rendering (CRI) – colour quality

16. Colour rendering (CRI) – colour quality

17. Colour rendering (CRI) – colour quality
High pressure mercury

18. Lighting technologies

19. Lighting technologies

20. 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"

21. LEDs
Nobel prize communication
p n
direct bandgap needed!

22. 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 using seed layers
+ conditions to create p-doping

23. History of LEDs

24. History of LEDs

25. History of LEDs
Nobel prize communication

26. RGB LEDs for general lighting?
Colour rendering Luminous efficacy

27. Lighting technologies
Source: OSRAM
(In,Ga)N
(Al,Ga,In)P
Green gap

28. White LEDs
Schubert, Light Emitting Diodes

29. Lighting technologies
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Blue
LED
Y3Al5O12:Ce
yellow phosphor
.new application
..new requirements
...new phosphors
Materials 2010, 3, 2834-2883

31. Phosphors for LEDs
Thousands of different phosphors can be made...
Main luminescent ions Main host constituents
Example: “YAG:Ce” = Y2.97Ce0.03Al5O12

32. Photoluminescence

33. 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...)

34. Phosphors for LEDs
6 (scientific) requirements for LED phosphors
• Suitable emission spectrum
• Strong absorption at +/- 460nm
• High (quantum) efficiency
• Chemically stable
• Short luminescence lifetime (no saturation)
• Thermal stability
P.F. Smet et al., J. Electrochem. Soc., 2011, 158, R37-R54

35. Phosphors for LEDs
P.F. Smet et al., J. Electrochem. Soc., 2011, 158, R37-R54

36. Photoluminescence
Dorenbos, J. Luminesc. (2003); Smet, J. Electrochem. Soc. (2011)
Tunability of Eu2+ based phosphors

37. Phosphors for LEDs
Only handful of phosphors are
suitable for high brightness LEDs
6 (scientific) requirements for LED phosphors
• Suitable emission spectrum
• Strong absorption at +/- 460nm
• High (quantum) efficiency
• Chemically stable
• Short luminescence lifetime (no saturation)
• Thermal stability
LED
Heat sink
Phosphor
P.F. Smet et al., J. Electrochem. Soc., 2011, 158, R37-R54

38. 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

39. Mn4+ - New kid on the block
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(arb. units)
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excitation emission
λem = 630 nm λex = 455 nm
K2SiF6:Mn4+

40. Mn4+ adds saturated & efficient red emission
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41. But...
DOI: 10.1149/2.0051601jssECS Journal of Solid State Science and Technology, 5 (1) R3040-R3048 (2016)

42. Application: remote phosphors
CdSe/CdS QDs
SrGa2S4:Eu2+
Blue LED

44. OLEDs
lightrabbit.ie

45. OLEDs
Flexible, curved, transparent displays
www.cdtltd.co.uk, http://news.oled-display.net/

46. OLEDs for general lighting (?)
WHITEvoid – Philips – 3D structures with OLEDs

47. Projection – point sources
display-central.com

48. General lighting: switch to LED
Replacement scheme and timing
• domestic use
• office/factory lighting
• public spaces
• sports arena
• transport

49. LiFi

50. Variable emission colours
Added value to lighting
Controlled with smart phone (via WiFi bridge)
Not fully RGB!
Circadian rhythm

51. Smart textiles

52. Light source of the future! Future shape?
Google images “LED lamp”

53. Light source of the future! Future shape?
Google images “LED lamp” + design