Transient light induced grating study of excitation diffusion in Y3Sc2Ga3O12 laser crystals

Excitation migration over the lower energy levels in Y₃Sc₂Ga₃O₁₂ (YSGG) laser crystals doped with Cr, Er, Tm, and Ho ions was studied using the two-wave mixing light induced grating (LIG) technique. The results of the LIG measurements were compared to the data obtained from the luminescence kinetics and spectra overlap studies of the migration. The comparison of the three different spectroscopic techniques allowed more detailed analysis of the complicated pattern of the energy transfer processes in the crystals than any one method alone. The migration was found to be very efficient, especially in highly doped crystals. The diffusion coefficients determined from direct LIG measurements were much higher than those calculated in dipole-dipole approximation from absorption and emission spectral measurements. This implies stronger than dipole-dipole coupling between interacting ions. In Tm doped crystals a surprisingly strong increase of the migration efficiency between Tm concentrations 8 × 10²⁰ cm^?3 and 1.5 × 10²¹ cm^?3 was observed both in LIG diffusion and luminescence kinetics experiments. This too cannot be explained in terms of low multipolar energy transfer. Exchange energy transfer and the percolation model are discussed as possible explanations for the experimental results.