Evaluation of Phosphor Materials for 4K Laser Projector
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Phosphor converted warm white light with high luminous efficacy and color rendering index is crucial for the future of blue diode laser driven lightning and display technologies. Particularly in projection displays where the high power (over 150 W) blue laser source is focused on the phosphor, the ideal phosphor candidate should provide better conversion efficiency, longer lifetime (20000 hours) and lower thermal overheat. We have characterized Ce doped single crystals as stationary phosphor candidates for blue laser driven solid lighting without heatsink. The luminous properties of the single crystals are improved when compared to the commercial phosphor wheels (Ce3+: Y3Al5O12) and luminous efficacy over 250 lm/W was achieved. The high-power blue diode laser driven temperature increase versus quantum efficiency change is discussed. The specific effect of temperature on quantum efficiency: when the temperature is less than a special value, the quantum efficiency increases with increasing temperature; when the temperature is greater than this special value, the quantum efficiency decreases with increasing temperature. This special value is called “Quenching Temperature”, and the increase in quantum efficiency is very gentle, but the reduction in quantum efficiency is very rapid. The experimental results show that the existence of Gd element greatly reduces the quenching temperature. This means that the phosphor containing the Gd element cannot be used under high power lasers. In Ce doped single crystals phosphor, the quenching temperature is increased when compared to the polycrystalline crystal phosphor. The ideal geometry and design of these Ce doped single crystals can serve as potential phosphors candidates for high-power blue diode laser driven projectors.