Thermally Activated Degradation of Remote Phosphors for Application in LED Lighting

This paper reports on an extensive analysis of the degradation of remote phosphors for solid-state lighting applications. The study is based on combined optical and thermal measurements, carried out before and during long-term stress tests, and provides the following results: 1) During normal operation, phosphors can show significant self-heating; 2) as a consequence of self-heating, the conversion efficiency of the phosphors decreases; and 3) exposure to long-term stress tests at moderate/high temperature levels (in the range of 85 °C-145 °C) can lead to remarkable degradation of the phosphors. Degradation mainly consists in a decrease in conversion efficiency and in worsening of the chromatic properties of the light-emitting diode-phosphor system. Finally, an activation energy value of 1.2 eV was extrapolated for the thermally activated degradation of the phosphors.