Presentation on the history of lighting and the role of phosphors (luminescent materials) in lighting. From fluorescence lamps to white light emitting diodes (LEDs) for displays and general lighting.

1. Phosphors...
and the future of lighting
philippe.smet@ugent.be - @pfsmet
TechBoost – Ghent University – April 28 2015
Philippe F. Smet, Heleen Sijbom, Sofie Abé, Jonas Joos,
Koen Van den Eeckhout, Zeger Hens, Dirk Poelman

2. The very beginning...

3. Our star:
A stable light source for billions of years...

4. Artificial light sources needed
• Burning fuels
• Extremely low efficiencies (~ 1%)
• By-products
Roman oil lamp

5. Incandescence

6. ° 1802 – Humphry Davy
Battery + platinum wire
° 1878 – Thomas Edison
Carbonized bamboo filament
Incandescence

7. Lamp efficiency: lumen/Watt

8. Fluorescence lamp
UV emission from Hg

9. Lamp efficiency: lumen/Watt

10. Fluorescence lamp
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+)

11. LEDs – light emitting diodes
Isamu Akasaki Hiroshi Amano Shuji Nakamura
"for the invention of efficient blue light-emitting diodes (LED’s)
which has enabled bright and energy-saving white light sources"

12. Making white light – RGB LED method
Source: OSRAM
(In,Ga)N
(Al,Ga,In)P

13. Making white light – RGB LED method
B
G
R
 4 LEDs needed for good color rendering
 Smart light sources
 Dimming issues
 Differential ageing
LER (lumen/Watt)Colour quality (../100) Spectrum (3000K)

14. Phosphor converted LEDs – early days
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

15. Lamp efficiency

17. What are phosphors?
Thousands of different phosphors can be made...
Main luminescent ions Main host constituents
Example: “YAG:Ce” = Y2.97Ce0.03Al5O12

18. 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...)

19. Requirements for phosphors
1. an appropriate emission spectrum
2. strong absorption and overlap with pumping LED
3. high quantum efficiency
4. chemical stability
5. short luminescence lifetime (no saturation)
6. thermally stable emission colour and intensity
^ scientific
Journal of The Electrochemical Society, 158 (6) R37-R54 (2011)

20. Main issue: red phosphors
Dorenbos, J. Luminesc. (2003); Smet, J. Electrochem. Soc. (2011)
Tunability of Eu2+ based phosphors

21. Remote phosphor approach
Blue LED chips
On-chip phosphor
White reflective cavity
Remote phosphor layer

22. Remote phosphor approach
lower blue photon flux
lower phosphor temperature
lower absorption losses (LED chips, connections)
higher phosphor cost!
glare reduction

23. Remote phosphor approach
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+

24. Remote phosphor approach
0
1
2
3
4
5
400 500 600 700
Normalized
intensity
(a.u.)
Wavelength (nm)

25. Remote phosphors for backlights
SrGa2S4:Eu2+
CdSe/CdS QDs
White remote phosphor LED

26. Remote phosphors for backlights
White remote phosphor LED

27. Phosphor based LEDs – final technology?
General lighting – Yes
Displays - ???
(OLEDs, full LED, laser)

28. lumilab.ugent.be
nb-photonics.ugent.be
philippe.smet@ugent.be
@pfsmet
Thank you for your attention!
http://lumicor-sbo.be