Phosphor Performance under High Intensity Excitation by InGaN Laser Diodes

Abstract

Excitation of phosphors by blue (InGaN) laser diodes is a new area in solid-state lighting applications that is getting notable attention. Such laser-activated remote phosphor (LARP) configurations generate luminances exceeding the brightest high-power LEDs by factors of 2–10, while simultaneously achieving high luminous fluxes in the range of 100s–1000s lumens. To fully take advantage of the LARP approach, a strong understanding of high-intensity phosphor excitation is needed. We develop a general rate-equation model to describe intensity quenching, applicable to common Ce 3+ - and Eu 2+ -based phosphors. The model includes the potential impact of traps and recombination from the conduction band. We also simulate the nonlinear propagation of pump and converted light to allow direct comparisons to experimental data. For YAG:Ce and LuAG:Ce model systems, we show that energy-transfer (ET) upconversion to the conduction band likely constitutes the main loss mechanism in high intensity laser pumping. We also show conclusively, via steady-state, low-temperature intensity quenching measurements, that high-intensity excitation alone can be responsible for large drops in quantum efficiency, without the complicating experimental factors of thermal quenching or short-pulse excitation to minimize heating.