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 temperatures ranging from 10 to 310 K, and the absorption spectra were measured at room temperature and 77 K. Spectroscopic analysis of the absorption and the emission spectra is performed on the basis of a distorted tetrahedral symmetry for the Cr4+ Site, namely C3v. The tetravalent chromium substitutes for Si4+ in this crystal, and there is no evidence for the presence of chromium in any other valence state. The Cr4+ site is characterized by strong crystal field parameters. We have tentatively assigned the sharp line at 1146 nm in the low-temperature fluorescence spectrum (excited by 1064-nm radiation) to the spin-forbidden singlet-to-triplet transition 1E-3A2, and the broad band with the peak at 1225 nm to the spin-allowed 3T2-3A2 transition. Excitation at 532 nm results in an additional type of emission in the near infrared. A similar dependence of the lasing wavelength on the pump wavelength was observed in the laser operation of the crystal at 77 K et al., in Advanced 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].