Ceramic converter for LEDs. Change light to white. Simon Korte

Transcription

1 Ceramic converter for LEDs Change light to white Simon Korte

2 Introduction LEDs Converters Possible Materials Advantages and Disadvantages Future Applications 2

3 Introduction Popstars of Science Shuji Nakamura Discovery of p-type doped GaN Development of LEDs with white Light and blue Laser diodes 3

4 Introduction Popstars of Science His employer Nichia abandon his Project on GaN Continued work on GaN Succeeded in 1993 Got 150 for his invention won an appeal for 20 billion (~US$180 million) But Nichia and Nakamura settled in 2005 for 840 million (~US$9 million) Highest bonus ever paid by a Japanese company 4

5 LED Structure of a LED 5

6 N-doped Layer P in Si crystal One additional electron Electron is accessible for electric conduction ( is located in the Conduction band) if a current is applied, the additional electrons is freely movable and Si crystal becomes a conductor If the electron is moved, it leave a localized positive charge 6

7 P-Doped Layer Al in Si crystal One Valenselectron is missing A hole is created If a electric current is applied, holes act like electrons Move freely in the valensband 7

8 LED Working Prinziple of a semicondutor LED Band-to-Band Transition Free-excition annihilation Localized excitions recombine at potential fluctuations in the band 8

9 LED Working Prinziple of a semicondutor LED Current is applied Recombination of electrons and holes at the p/n junction Photon energy is determined by the Bandgap Through p/n-doping electrons and holes are highly accessible for this process 9

10 Converter To convert convertere [Lat.] Convertere = to turn around 10

11 Converter Principle of a Converter 11

12 Converter Example of a Pc-LED 12

13 Converter Attributes of a Converter Requirements for a good Converter Spin- and parity-allowed transition Strong Absorption of the wavelength emitted by the LED High stability against degradation via O 2,CO 2 and H 2 O Easy to handle within LED production process Quantum efficiency > 90% Stable at high excitation density ( W/cm 2 ) Possible Activator Ions: 13

14 Converter Possible Materials Anorganic Phosphores Microrange (Ca,Sr,Ba)Si 2 N 2 O 2 :Eu 2+ (Ca,Sr,Ba)2SiO4:Eu 2+ (Ca,Sr)S:Eu 2+ Nano Pigments Quantom Dots (In,Ga)P Organic dies Polycyclic aromatic Substances like Perylene Metal-Organo-Komplexes like cis-bis(4,4 -bipyridindicarboxylato)di(thiocyanato)ruthenium(ii) 14

15 Converter Possible Materials with Ce and Eu Many possible Materials for inorganic converters but many of them are not: cost effective Free to use because of patents A sufficient Quantum Efficiency Chemically stable Unaffected by thermal Quenching Blessed with the right absorption Emit the wanted wavelength 15

16 Converters Example Emission in yellow & red warm light Good color rendering, comparable to a halogen lamp Quantum efficiency lower than 150lm/W Reasons are: Re-absorption, scattering 16

17 Ceremics Are inorganic, non-metallic polycrystalline Materials Powder is mixed with organic binder and a Liquid This raw material can be processed and then sintered at high T Typical Materials: Al 2 O 3, BN or SiC Typical Attributes of a ceramic are: Hard & brittle Withstand very high Temperatures (T>1600 C) Withstand chemical erosion Easy to shape before sintering Very dense and continuous Material 17

18 Advantages of ceramic Converters Homogeneous Layer Thickness Less colour point variation Higher heat conductivity (oxide-based ceramics: 5 15 W/m K vs. transparent silicones 0.1 to 0.4 W/m K less thermal Quenching + higher Efficiency Easy Handling by Pick & Place Lower Activator Content because of the dense and continues body Lowers the self-absorption of Ce3+ for example Reduced surface & less degradation 18

19 Disadvantages of ceramic Converters Complex and expensive production Blending of different Phosphors is very difficult Porosity & grain size have huge influence due to scattering Not every phosphor can be sintered without loosing some of his properties 19

20 Future Application 20

21 Future Application Light is everywhere Heat source Lighting at night Very inefficient Replacing every light source in average and scientific life Compact Efficient λ is adjustable 21

22 22