Laser-induced grating spectroscopy of Cr 3+-doped Gd 3Ga 5O 12 and Gd 3Sc 2Ga 3O 12 crystals

Abstract

The absorption and fluorescence spectra and fluorescence lifetimes of Cr 3+ ions in two garnet hosts, Gd 3Ga 5O 12 and Gd 3Sc 2Ga 3O 12, were measured as a function of temperature. In addition, laser-induced grating measurements were made as a function of laser power and write beam crossing angle for various temperatures between 10 and 300 K. For short writing times, Cr 3+ population gratings are produced and the observed signal dynamics were used to determine the properties of exciton migration in these materials. The exciton diffusion coefficient for Gd 3Ga 5O 12:Cr 3+ was found to decrease as temperature is raised while in Gd 3Sc 2Ga 3O 12:Cr 3+ the diffusion coefficient increases. Contributions to the laser-induced gratings from absorption and dispersion changes were determined and this was used to provide information on radiationless decay and excited state absorption processes. The differences in the results obtained on these two materials are attributed to the spectral effects produced by the different crystal field splittings of the Cr 3+ energy levels. For long writing times, long-lived changes in the refractive index were also observed and attributed to optically induced color centers.