Optical properties of tsavorite Ca3Al2(SiO4)3:Cr3+, V3+ from Kenya

Abstract

Previously, a relatively large splitting of the 2Eg state of Cr3+ in grossular Ca3Al2[SiO4]3 has been reported [M. Czaja and Z. Mazurak, Opt. Mater 3 (1994) 95]. The absorption and luminescence spectra of crystals containing Cr3+ and V3+in grossular Ca3Al2(SiO4)3 garnets (variety tsavorite) have been studied for the first time. From these spectra measured at room and liquid helium temperatures we determined energies of R2, R1, and 4T2g levels of Cr3+. The lifetimes and splitting of the 2Eg state have been measured by tuning the excitation energy within the inhomogeneous profile of the R1 and R2 lines of the split 2Eg → 4A2g transition. To account for the thermal quenching of the R-lines, it is necessary to recognize that the two components of the doublet may have remarkably different radiative lifetimes (7500 and 2500 μs). These lifetimes were obtained from low temperature decay and from the temperature dependence of the intensity ratio of the R2, R1 components. These separate lifetimes as well as the lifetime of the 4T2g state were then set to fit the temperature dependence of the joint effective lifetime. The optical fluorescence of a V3+ dopant is characterized by the broad band infrared fluorescence spectrum associated with short decay time < 1μs.