Enhancing opto-thermal performances of the reflective phosphor-converted laser diode by stacking a sapphire substrate for double-sided phosphor cooling

Abstract

Phosphor-converted laser diode (pc-LD) has been a very competitive candidate in high-luminance white illumination. For the reflective pc-LD, the phosphor layer is usually bonded onto a reflective substrate, which plays the role of light reflection and heat dissipation. However, the heat generation of phosphor cannot be efficiently dissipated by only cooling the reflective surface, in which case most of heat may be confined in the phosphor layer with low thermal conductivity. In this work, a double-sided phosphor cooling scheme was presented to improve the opto-thermal performances of the reflective pc-LD by stacking a highly transparent and heat-conducting sapphire substrate onto the phosphor layer. By using an opto-thermal phosphor model, it was found that the maximum heat generation density and hotspot were both confined at the incident surface. After stacking a sapphire substrate onto the incident surface, the maximum heat was extracted and conducted from the sapphire substrate to the reflective substrate, leading to a significant decrease of the maximum phosphor temperature from 221 °C to 86 °C under excitation power of 0.8 W. In this case, a higher excitation power was allowed, contributing to a higher attainable output power and luminance. The double-sided phosphor cooling scheme was also experimentally achieved. It was found that the presented scheme exhibited higher optical power, luminance and color stability than the traditional one under higher excitation power.