Unveiling the effect of Ce3+ doping concentration in YAG:Ce single crystals towards high luminance laser lighting

Abstract

Doping concentration of a phosphor is key parameter, affecting multiple properties such as light absorption, quantum yield, luminescence decay, thermal conductivity, and thermal quenching, etc. These properties could directly influence the luminous efficacy, the saturation threshold, and the emitting area of the phosphor when irradiated by laser, thus determining the peak luminance of a phosphor-converted laser lighting device. But surprisingly no systematic investigation has been done to research the effect of phosphor doping concentration on the luminance performance of laser lighting. Here we report the YAG:Ce single crystal phosphors with different Ce3+-doping concentrations (between 0.05 at% and 0.30 at%) and thicknesses (0.15 mm–0.45 mm). The relationship between Ce3+ concentration, phosphor thickness, and the colorimetric/photometric parameters (luminous efficacy, luminous flux, luminance) are built and elucidated. It is found that the thinner sample with higher doping density tends to be saturated at lower laser power density (314.1 W/mm2) and the device shows lower luminance. This result is also verified by thermal simulation that the corresponding sample shows highest working temperature. Remarkably, the optimal sample with thickness of 0.45 mm and Ce3+ density of 0.30 at% presents a record high luminous exitance of 33414 lm/mm2 and a record high luminance of 10636 Mcd/m2, indicating potential for use in special lighting, projector, and optical communication fields.