TechBoost 2015 - Ghent University - Phosphors for lighting

Phosphors... and the future of lighting

[email protected] - @pfsmet

TechBoost – Ghent University – April 28 2015

Philippe F. Smet, Heleen Sijbom, Sofie Abé, Jonas Joos, Koen Van den Eeckhout, Zeger Hens, Dirk Poelman

The very beginning...

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

Artificial light sources needed

• Burning fuels • Extremely low efficiencies (~ 1%) • By-products

Roman oil lamp

Incandescence

° 1802 – Humphry Davy

Battery + platinum wire

° 1878 – Thomas Edison

Carbonized bamboo filament

Incandescence

Lamp efficiency: lumen/Watt

Fluorescence lamp

UV emission from Hg

Lamp efficiency: lumen/Watt

Fluorescence lamp

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Emission wavelength (nm)

Inte

nsi

ty

Tb3+

Tb3+

Eu3+

Hg

254nm

(La,Ce)PO4:Tb3+

Y2O3:Eu3+

(BaMgAl10O17:Eu2+)

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"

Making white light – RGB LED method

Source: OSRAM

(In,Ga)N

(Al,Ga,In)P

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)

Phosphor converted LEDs – early days

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Wavelength (nm)

Blue LED

Y3Al5O12:Ce yellow phosphor

.new application

..new requirements

...new phosphors

Lamp efficiency

What are phosphors?

Thousands of different phosphors can be made...

Main luminescent ions Main host constituents

Example: “YAG:Ce” = Y2.97Ce0.03Al5O12

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...)

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)

Main issue: red phosphors

Dorenbos, J. Luminesc. (2003); Smet, J. Electrochem. Soc. (2011)

Tunability of Eu2+ based phosphors

Remote phosphor approach

Blue LED chips

On-chip phosphor

White reflective cavity

Remote phosphor layer

Remote phosphor approach

lower blue photon flux

lower phosphor temperature

lower absorption losses (LED chips, connections)

higher phosphor cost!

glare reduction

Remote phosphor approach

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Intensity (arb. units)

Wavelength (nm)

excitation emission λem = 630 nm λex = 455 nm

K2SiF6:Mn4+

Remote phosphor approach

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Normalized intensity (a.u.)

Wavelength (nm)

Remote phosphors for backlights

SrGa2S4:Eu2+

CdSe/CdS QDs

White remote phosphor LED

Remote phosphors for backlights

White remote phosphor LED

Phosphor based LEDs – final technology?

General lighting – Yes Displays - ??? (OLEDs, full LED, laser)

lumilab.ugent.be nb-photonics.ugent.be

[email protected] @pfsmet

Thank you for your attention!

http://lumicor-sbo.be