SPECTROSCOPY AND DYNAMICS OF CR4+ Y3AL5O12

We present a spectroscopic overview of Cr4+-doped Y3Al5O12 (YAG), a ne w laser material for the near-infrared region (NIR). It is found that only 2% of the Cr ions are tetrahedrally coordinated Cr4+. However, th e optical spectra are dominated by this ion. The missing inversion sym metry for the tetrahedral site causes higher cross sections than are c ommon for octahedrally coordinated ions. The experimental data include a survey of the absorption and emission features. Lifetime measuremen ts, as well as piezospectroscopic experiments yield additional spectro scopic information. Our data suggest an energy-level assignment that i s different from the one previously used to describe the spectrum. Ins tead of ascribing the strong NIR absorption band, centered at around 1 000 nm, to the B-3(1)(3A2)double-line arrow pointing right 3E(3T2) tra nsition, we assign it to the B-3(1)(3A2) double-line arrow pointing ri ght 3A2(3T1) transition. This assignment is able to describe the polar ization-dependent spectra, the piezospectroscopic results, and the res ults from earlier polarization-dependent saturation experiments. An an alysis of the luminescence decay rate yields quantum efficiencies of a round 49% at 10 K and 15% at room temperature, resulting in a peak emi ssion cross section of 3.5 X 10(-19) cm2.