On the stability and reliability of Sr_1-xBa_xSi_2O_2N_2:Eu^2+ phosphors for white LED applications

Abstract

Sr1-xBaxSi2O2N2:Eu2+ phosphors were synthesized using high temperature solid state reactions and the reliability of the as-synthesized phosphors for White LED applications was investigated. The oxidation resistance of the phosphors was investigated by baking the phosphors at various temperatures in air for 2 hours and also at 85 °C, 85% relative humidity for 150 hours. The photo stability of the phosphor was studied by illuminating the phosphor using a high power laser diode (450 nm) at various laser fluxes. Phosphor converted LEDs were fabricated using the as-synthesized Sr1-xBaxSi2O2N2:Eu2+ (x = 0 and 0.40) phosphors. The long term stability of the fabricated LEDs was tested by keeping the LEDs at 85 °C and 85% relative humidity for 800 hrs. Even though phosphors show high thermal and chemical stability, the electroluminescent (EL) intensity of the fabricated LEDs drops by 15% after 800 hrs of operation. The degradation of EL intensity of the device might be the result of thermally assisted photo-ionization of Eu2+ ions in the phosphor.