Near-Infrared Luminescence in Cr, Ca-Doped Yttrium Aluminum Garnet

Abstract

We have studied the near-infrared (NIR) absorption and fluorescence spectra of Cr,Ca-doped YAG single-crystal fibers at temperatures of 12 to 290 K. The NIR spectra are attributed to transitions between the 3A2 and 3T2 states of tetrahedral Cr4+. At 12 K the fluorescence spectrum has a sharp electronic transition at 1280 nm and a broad sideband centered at approximately 1400 nm, while the absorption spectrum has only a broad band centered at 1050 nm. The fluorescence lifetime is 42 ± 4 μs at 12 K and 3 ± 1 μs at room temperature. An additional sharp fluorescence line is observed at 1160 nm with a lifetime of 95 ± 5 μs. This line is attributed to a Cr4+ site with a different local perturbation due either to a different placement of the Ca2+ charge compensator or proximity of a Cr3+ or Cr4+.