Low-temperature high-pressure spectroscopy of lanthanum lutetium gallium garnet crystals doped withCr3+andNd3+

Abstract

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.