Titanium doped sapphire and YAG have been proposed as materials for tunable solid state lasers, using the d→d, nominally 2E → 2T2, vibronic band of Ti3+ around 800 nm. (1,2) At liquid-helium temperatures relatively sharp zero-phonon lines (ZPL) associated with the 2E → 2T2 transitions are observed at 616 nm (Al2O3) and 650 nm (YAG). We have investigated the photo-stability of the Ti3+ ions in these two hosts under resonant pumping of the zero-phonon line. Frequency-selective excitation in the inhomogeneously broadened ZPL permits sensitive detection of the photo-induced reduction of Ti3+ ions.
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