Bulk and local elastic relaxation around optically excited centers.

Abstract

The macroscopic refractive effect arising from an optically excited ${\mathrm{Cr}}^{3+}$ center in a Gd-Sc-Ga garnet crystal was observed and measured using time-resolved beam-deflection spectroscopy. The excited-state effect is much larger than the thermal effect. The predominant mechanism is concluded to be the refractive effect stemming from the elastic dilation of the ${\mathrm{CrO}}_{6}$ cluster in the excited $^{4}$${\mathit{T}}_{2}$ state of ${\mathrm{Cr}}^{3+}$. The bulk expansion per excited ion is \ensuremath{\approxeq}12 A${\mathrm{\r{}}}^{3}$. An expansion of \ensuremath{\approxeq}0.13 \AA{} of the oxygen coordination sphere is derived in the approximation of an isotropic elastic continuum and a fully symmetric dilation. This displacement is in agreement with the optical spectra in the framework of the configuration coordinate model.