Sr-Sialon Phosphor for White LEDs with High Efficiency and High Color Rendering

White light-emitting diodes (LEDs) are promising devices for solid-state lighting and LCD backlights. Demand for high color rendering and high efficiency is expected to increase in the future.

Toshiba has developed two new types of phosphor based on strontium (Sr)-containing sialon for white LEDs with high efficiency and high color rendering. One is a greenemitting phosphor, Sr₃Si₁₃Al₃O₂N₂₁:Eu²⁺, whose external quantum efficiency is 67%, and the other is a red-emitting phosphor, Sr₂Si₇Al₃ON₁₃:Eu²⁺, with an external quantum efficiency of 61% for blue LED excitation. Since these phosphors also have the advantage of exhibiting relatively small thermal quenching, they maintain high efficiency under high-power driving when the device temperature drastically rises. White LEDs were fabricated using these newly developed phosphors combined with a blue highpower LED. The luminous efficacy and color rendering index Ra of the LED for typical white (4 500 K) at currents of 20 mA and 350 mA were 72 lm/W (Ra 85) and 50 lm/W (Ra 85), respectively.

The LEDs show small reduction of the luminous efficacy and high color rendering under high-power driving.

Crystal structure of new green sialon phosphor

Emission spectra of fabricated high-color-rendering white LED
with new green and red sialon phosphors driven at various currents