Temperature dependence of the vibronic spectrum and fluorescence lifetime of YAG:Cr³⁺

Abstract

The authors have investigated the vibronic spectrum associated with the 2E to 4A2 transition of YAG:Cr3+ in the temperature region 10-300 K. At low temperatures vibrational satellites corresponding to spontaneous phonon emission are observed only on the low energy side of the nophonon R lines which are located at 6863.2 and 6872.6 AA. At higher temperatures, vibronic emission appears also on the high energy side, corresponding to phonon absorption. With increasing temperature, the vibronic bands become more intense relative to the R lines, the peaks broaden, and a fluorescence continuum extends from 6500 to 8000 AA. The fluorescence lifetime of the 2E level which is 8.5 ms at 77 K decreases rapidly above 150 K at 1.6 ms at 300 K. The enhancement of the transition probability of the vibronic emission can account for the major temperature dependence of the fluorescence lifetime without requiring the contribution of purely nonradiative transitions. For this case a calculation of the purely radiative lifetimes can be made. The values are found to be tau rad(R1) approximately 0.07 s and tau rad(R2) approximately 0.09 s.