OPTICAL SPECTROSCOPY OF CR4+-Y2SIO5

Spectroscopic data on the absorption and the fluorescence spectra and fluorescence lifetimes are presented for Cr4+:Y2SiO5, the newest Cr4+- doped laser crystal. The fluorescence measurements were conducted at t emperatures ranging from 10 to 310 K, and the absorption spectra were measured at room temperature and 77 K. Spectroscopic analysis of the a bsorption and the emission spectra is performed on the basis of a dist orted tetrahedral symmetry for the Cr4+ Site, namely C3v. The tetraval ent chromium substitutes for Si4+ in this crystal, and there is no evi dence for the presence of chromium in any other valence state. The Cr4 + site is characterized by strong crystal field parameters. We have te ntatively assigned the sharp line at 1146 nm in the low-temperature fl uorescence spectrum (excited by 1064-nm radiation) to the spin-forbidd en singlet-to-triplet transition 1E-3A2, and the broad band with the p eak at 1225 nm to the spin-allowed 3T2-3A2 transition. Excitation at 5 32 nm results in an additional type of emission in the near infrared. A similar dependence of the lasing wavelength on the pump wavelength w as observed in the laser operation of the crystal at 77 K et al., in A dvanced Solid-State Lasers, L. L. Chase and A. A. Pinto, eds., Vol. 13 of OSA Proceedings Series (Optical Society of America, Washington, D. C., 1992), pp. 28-30].