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The results of the absorption and photocurrent measurements and light-induced grating spectroscopy of undoped LaGaO3 crystals near room temperature are presented. Several absorption bands in the visible and near-ultraviolet region have been detected. Reversible photochromic effect has been observed in the nonoxidized crystals. The results of measurements show that the main absorption band in crystals annealed in air, peaked at 22 500 cm, which also coincides with the main band in the photocurrent spectrum, is associated with the hole-related defect. The diffusion of holes is revealed in the light-induced grating’s experiments. The diffusion is thermally activated with an activation energy equal to 0.7560.03 eV. This value of the activation energy of hole diffusion is responsible for large changes of the diffusion coefficients, which increase more than two orders of magnitude between 20° and 70 °C. @S0163-1829~99!00448-8#

Low-temperature luminescence measurements under high pressures in diamond-anvil cell of nonstoichiometric lanthanum lutetium gallium garnet (LLGG) doped with Cr 3 + ions and nonintentionally with Nd 3 + ions are reported.Three nonequivalent Cr 3 + centers were found in the crystal using this technique. The results also reveal information about the electronic structure of different Cr 3 + centers in those crystals. Cr 3 + ions in a LLGG crystal experience a very low crystal field strength. The energy differences between the 4 T 2 and 2 E levels are negative, and equal to about - 1100 cm - for two of those centers and about -1500 cm - 1 for the third one. The spectral results were corroborated by a theoretical analysis of the luminescence decay times as a function of pressure, which allowed one to establish the exact values of the crystal-field parameter Dq at ambient pressure for those centers. The crystal exhibits a large inhomogeneous broadening of the R lines, associated with nonstoichiometry. In addition to the Cr 3 + luminescence also luminescence of Nd 3 + ions was detected in the LLGG crystals. One of the Nd 3 + luminescence lines, associated with the 4 F 3 / 2 4 I 9 / 2 transition. is strongly dependent on pressure, with a pressure coefficient equal to 0.96′0.02 cm - 1 /kbar, which makes this system interesting as a pressure gauge in the infrared region.