A significant obstacle in the development of phosphor-converted white-laser diodes (pc-wLDs) is associated with the laser-induced luminescence saturation of phosphors. YAG:Ce is a canonical yellow-emitting phosphor. However, there has been no few systematic research of measurement and understanding of the luminescence saturation in YAG:Ce yet. Here, we analyze the luminescence saturation of a single-crystal YAG:Ce with a unique phosphor geometry. A novel characterization method, which enables the optical signals to be fully collected and analyzed, is introduced. The effects of both laser power and laser power density on the luminescence properties and colorimetric properties of the YAG:Ce are studied systematically. The results show that a single-crystal YAG:Ce has a high saturation threshold (over 360 W/mm 2 ) so that only a very slight saturation behavior can be observed at a high power density. Furthermore, a pc-wLDs light source based on the combination of a single laser diode and a YAG:Ce phosphor exhibits remarkable efficiency and stability. Under the excitation of a 3.38 W blue laser (~100 W/mm 2 ), the white light emission with the luminous flux of 465 lm, the luminous 2 / 23 efficacy (LE) of 145 lm/W, and the correlated color temperature (CCT) of 4980 K can be achieved.
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We report observations of saturation effects in a Ce:LuAG and Eu-doped nitride ceramic phosphor for conversion of blue laser light for white light generation. The luminous flux from the phosphors material increases linearly with the input power until saturation effects limit the conversion. It is shown that the temperature of the phosphor layer influences the saturation power level and the conversion efficiency. It is also shown that the correlated color temperature (CCT), phosphor conversion efficiency and color rendering index (CRI) are dependent both on the incident power and spot size diameter of the illumination. A phosphor conversion efficiency up to 140.8 lm/W with CRI of 89.4 was achieved. The saturation in a ceramic phosphor, when illuminated by high intensity laser diodes, is estimated to play the main role in limiting the available luminance from laser-based lighting systems.
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