An optical-thermal model for laser-excited remote phosphor with thermal quenching

Laser-excited remote phosphor (LERP) has been reported to be an effective approach to produce high-luminance white light based on laser diodes (LDs). However, the local phosphor temperature may easily reach thermal quenching point due to the local high light power density, resulting in a significant drop/deterioration of efficiency, reliability and lifetime. In this paper, we focused on the phosphor thermal quenching and developed an optical-thermal coupling model to predict the high phosphor temperature of LERP. From this model, both accurate phosphor heating and temperature can be obtained by iteration. For validation, experiments were performed to verify the model and good agreement was observed between the measurements and the theoretical predictions. Based on the validated model, the critical incident power against thermal quenching under various factors was systematically studied. It was found in the experiments that when a 680 mW laser spot with a diameter of 1.0 mm was projected onto a phosphor layer, the phosphor temperature was as high as 549.0 degrees C, which would result in severe thermal quenching and even silicone carbonization. It was also found that increasing pump spot from 0.5 mm to 3.0 mm can dramatically enhance critical power by 19 times. The effect of decreasing phosphor layer thickness on critical power enhancement was explained by the model. Some suggestions were also provided to prevent thermal quenching and improve the optical/thermal performance of LERP. (C) 2017 Elsevier Ltd. All rights reserved.