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

A quiz to get started!

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A: Sun LED Incandescent Fluorescent

B: Sun LED Incandescent Fluorescent

C: Sun LED Incandescent Fluorescent

D: Sun LED Incandescent Fluorescent

A brief history of lighting

Lighting technologies

Lighting technologies

° 1802 – Humphry Davy battery + Pt wire ° 1878 – Thomas Edison carbonized bamboo filament

Lighting technologies

lumen per Watt

Luminous efficacy of radiation (LER) – lumen/Watt

V(l)

93 lm/W

Correlated colour temperature (CCT)

CIE x,y colour diagram

Lighting technologies

15 lm/W

Lighting technologies

Mercury, 254nm (UV-C)

Lighting technologies

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Emission wavelength (nm)

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Tb3+

Tb3+

Eu3+

Hg

254nm

(La,Ce)PO4:Tb3+

Y2O3:Eu3+

(BaMgAl10O17:Eu2+)

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)

Luminescence

Credits: Samsung, Philips, TU Delft, Wikimedia, Highdisplay

LED

compact fluorescent

incandescent (halogen)

Pro/con of fluorescent lighting

Efficiency limit in fluorescent tubes: Stokes losses!

Colour rendering (CRI) – colour quality

Colour rendering (CRI) – colour quality

Colour rendering (CRI) – colour quality

High pressure mercury

Lighting technologies

Lighting technologies

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"

LEDs

Nobel prize communication

p n

direct bandgap needed!

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

History of LEDs

History of LEDs

History of LEDs

Nobel prize communication

RGB LEDs for general lighting?

Colour rendering Luminous efficacy

Lighting technologies

Source: OSRAM

(In,Ga)N

(Al,Ga,In)P

Green gap

White LEDs

Schubert, Light Emitting Diodes

Lighting technologies

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Blue LED

Y3Al5O12:Ce yellow phosphor

.new application

..new requirements

...new phosphors Materials 2010, 3, 2834-2883

Phosphors for LEDs

Thousands of different phosphors can be made...

Main luminescent ions Main host constituents

Example: “YAG:Ce” = Y2.97Ce0.03Al5O12

Photoluminescence

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...)

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

Phosphors for LEDs

P.F. Smet et al., J. Electrochem. Soc., 2011, 158, R37-R54

Photoluminescence

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

Tunability of Eu2+ based phosphors

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

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

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Philips LEDmaster

Mn4+ - New kid on the block

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Intensity (arb. units)

Wavelength (nm)

excitation emission λem = 630 nm λex = 455 nm

K2SiF6:Mn4+

Mn4+ adds saturated & efficient red emission

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Normalized intensity (a.u.)

Wavelength (nm)

But...

DOI: 10.1149/2.0051601jss ECS Journal of Solid State Science and Technology, 5 (1) R3040-R3048 (2016)

Application: remote phosphors

CdSe/CdS QDs

SrGa2S4:Eu2+

Blue LED

OLEDs

lightrabbit.ie

OLEDs

Flexible, curved, transparent displays

www.cdtltd.co.uk, http://news.oled-display.net/

OLEDs for general lighting (?)

WHITEvoid – Philips – 3D structures with OLEDs

Projection – point sources

display-central.com

General lighting: switch to LED

Replacement scheme and timing

• domestic use • office/factory lighting • public spaces • sports arena • transport

LiFi

Variable emission colours

Added value to lighting Controlled with smart phone (via WiFi bridge) Not fully RGB! Circadian rhythm

Smart textiles

Light source of the future! Future shape?

Google images “LED lamp”

Light source of the future! Future shape?

Google images “LED lamp” + design