OPTICAL-PROPERTIES OF TSAVORITE CA3AL2(SIO4)(3)CR3+,V3+ FROM KENYA

Previously, a relatively large splitting of the (2)E(g) state of Cr3in grossular Ca3Al2[SiO4](3) has been reported [M. Czaja and Z. Mazura k, 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 R(2), R(1), and T-4(2g) levels of Cr3+. The lifetimes and splitting of the (2)E(g) state have been measured by tuning the excita tion energy within the inhomogeneous profile of the R(1) and R(2) line s of the split (2)E(g) --> (4)A(2g) transition. To account for the the rmal quenching of the R-lines, it is necessary to recognize that the t wo components of the doublet may have remarkably different radiative l ifetimes (7500 and 2500 mu s). These lifetimes were obtained from low temperature decay and from the temperature dependence of the intensity ratio of the R(2), R(1) components. These separate lifetimes as well as the lifetime of the T-4(2g) state were then set to fit the temperat ure dependence of the joint effective lifetime. The optical fluorescen ce of a V3+ dopant is characterized by the broad band infrared fluores cence spectrum associated with short decay time < 1 mu s.