Unraveling the impact of different thermal quenching routes on the luminescence efficiency of the Y3Al5O12:Ce3+ phosphor for white light emitting diodes†
Cerium doped yttrium aluminium garnet, Y3−zCezAl5O12, is the prototype material for solid-state white lighting and it still is an important white LED phosphor. However, fundamental understanding of the thermal quenching of luminescence, which leads to a pronounced reduction of the emission intensity under high-power light-emitting diode operation, remains to be obtained. Here we show, through a multitechnique approach based on photoluminescence, thermoluminescence and mode-selective vibrational excitation experiments that thermal quenching of luminescence in Y3−zCezAl5O12 is caused by a combined effect of thermal ionization, thermally activated concentration quenching, and thermally activated 5d → 4f crossover relaxation via electron–phonon coupling, and establish the general trends upon variation of the Ce3+ concentration and temperature. Thermal quenching below 600 K is primarily the result of concentration quenching and crossover relaxation, which can be suppressed by keeping the Ce3+ dopant concentration far below 0.7 mol%, whereas for temperatures above 600 K thermal ionization is the predominating quenching process. This new insight into the interplay between different thermal quenching processes provides design principles for optimizing the light emittance and colour stability of new phosphor materials used in white lighting devices characterized by certain operating temperatures.