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 °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 °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.