Optical properties of solid-state laser lighting devices using SiAlON phosphor-glass composite films as wavelength converters

In this work, SiAlON phosphor-glass films were investigated as wavelength converters in solid-state laser lighting. The phosphor-glass composite films were prepared by dispersing phosphor powders into a silica precursor solution and sintering at 500 degrees C. Both simulation and experiment were carried out to evaluate the optical properties of solid-state lighting devices using SiAlON: Eu or YAG: Ce-glass films. The device using SiAlON: Eu phosphors initially has lower brightness than that of the device using YAG: Ce at lower laser powers, but the latter has an illuminance saturation at 1000 lx whereas the SiAlON-based device is free of saturation even at higher laser powers. The device using SiAlON phosphor-glass composite films has a maximum illuminance 15% higher than that of the device using YAG when the temperature exceeds 250 degrees C. These better optical properties are ascribed to the higher thermal stability of SiAlON phosphors that are able to achieve high luminance and thermally robust solid-state lighting. (C) 2016 The Japan Society of Applied Physics