Local structural changes in excited Ti3+:Al2O3 studied by time-resolved XANES

Transient changes in the local structure of optically excited Ti3+ ions in a Al2O3 single crystal are studied by time-resolved x-ray absorption spectroscopy. A model considering coupling of the excited E-2(C-3v) electronic state of the Ti3+ ion to the approximate A(1g)(O-h) and E-g(O-h) local vibrational modes of the TiO6 octahedron is constructed to fit the experimental data. We determine the magnitude of the A(1g)(O-h) mode and give an estimate of the E-g(O-h) Jahn-Teller distortion although this analysis does not distinguish between compression and elongation of the oxygen octahedron. Assuming a compressed octahedron, the E-g (O-h) distortion is found to be 0.14 +/- 0.02 angstrom with an A(1g)(O-h) mode of 0.066 +/- 0.006 angstrom. In the case of an elongated octahedron the E-g(O-h) distortion is -0.195 +/- 0.017 angstrom with an A(1g)(O-h) mode of 0.052 +/- 0.002 angstrom.