Fluorescence of inversion site Cr3+ ions in alexandrite

Abstract

A c‐axis alexandrite laser rod was longitudinally pumped in the 450–560 nm region with argon ion and dye lasers. In addition to the sharp R lines and broadband phonon‐assisted transitions typical of mirror site Cr³⁺ ions in alexandrite, room temperature fluorescence spectra displayed characteristics in the 690–730 nm region which were maximal when pumped at 496.5 nm but were nearly absent when pumped at 457.9 nm and 560 nm. Time‐dependent fluorescence measurements with pulsed excitation yielded two lifetimes, 310 μs and 44 ms. The short lifetime component is mirror site fluorescence. The long lifetime component is typical for Cr³⁺ ions in inversion symmetry sites and its presence correlates with the pump wavelength dependent features. Inversion site fluorescence consists of magnetic dipole R lines at 690.0 nm and 695.8 nm and phonon‐assisted electric dipole transitions at longer wavelengths.