Radiative and non-radiative transitions of excited Ti3+ cations in sapphire

We have measured the fluorescence quantum efficiency in Ti3+:sapphire single crystals between 150 K and 550 K. Using literature-given effective fluorescence lifetime temperature dependence, we show that the zero temperature radiative lifetime is (4.44 +/- 0.04) mu s, compared to the 3.85 mu s of the fluorescence lifetime. Fluorescence lifetime thermal shortening resolves into two parallel effects: radiative lifetime shortening, and non-radiative transition rate enhancement. The first is due to thermally enhanced occupation of a Delta E = 1,700cm(-1) higher (top) electronic state of the upper multiplet, exhibiting a transition oscillator strength off= 0.62, compared to only 0.013 of the bottom electronic state of the same multiplet. The non-radiative rate relates to multi-phonon decay transitions stimulated by the thermal phonon occupation. Thermal enhancement of the configuration potential anharmonicity is also observed. An empiric expression for the figure-of-anharmonicity temperature dependence is given as (H) over cap (T) = (H) over cap (0)(1 +beta exp(-(h) over bar omega(co)/k(B)T)), where (H) over cap (0) = 0.276, beta= 5.2, (h) over bar omega(co) = 908cm(-1), and k(B) is the Boltzmann constant.