Laser-Driven White Light Source With High Luminescence Saturation Through Reflective Color Converter

In this letter, a laser-driven white light source with high luminescence saturation was fabricated by combining blue laser chips and an Al2O3-doped reflective color converter. The reflective converter was prepared by printing and sintering an Al2O3-doped phosphor-in-glass (PiG) film on an AlN substrate. The Al2O3-PiG film with intact crystal structure of YAG phosphor is robustly bonded on the substrate. The optical and thermal performances of Al2O3-PiG based phosphor-converted white laser diodes (pc-WLDs) were optimized with different Al2O3 contents. The pc-WLD achieves a maximum saturation threshold of 25.2 W/mm2 and a high luminous flux of 2138 lm (luminance of 1260 Mcd $\cdot \text{m}^{-{2}}{)}$ . The working temperature of 6%-Al2O3-PiG is only 88.4°C, which is reduced by 33.5% compared with that of Al2O3-free-PiG. The fabricated small pc-WLD device has high-luminance white light, excellent collimation, and long illumination distance, which is a promising light source for high-brightness lighting.

I. Introduction

Laser lighting is regarded as a new-generation solid-state light source in lighting and display fields, such as car headlights, outdoor lamps, laser projectors, and medical treatments [1], [2], [3]. Compared with light-emitting diodes (LED), laser diodes (LD) has some advantages of no efficiency droop, high power and power density, long irradiation distance, and small beam divergence [4], [5], [6]. Nowadays, phosphor-converted white LD (pc-WLD) is a common white laser source in which a yellow color converter is excited by blue laser chips, including transmissive and reflective structure [7], [8]. The color converter must be able to tolerate high laser radiation energy and phosphor non-radiative heat. Owing to the poor heat resistance and low thermal conductivity of resin matrix, phosphor-in-resin converters have irreversible problems of thermal runaway and resin carbonization under high-power-density laser [9], [10], [11], [12].