Middle infrared luminescence of rare earth ions in silver halide crystals

Middle infrared laser systems for countermeasures against heat seeking missiles are currently under development. These systems, based on optical parametric oscillators, are complex, bulky and expensive. Middle-infrared fiber lasers emitting in the 3 - 5μm spectral region may provide an attractive alternative to the systems under development. We have investigated luminescence of silver bromide-chloride crystals and fibers doped with rare earth ions (e.g. Pr³⁺, Tb³⁺ and Nd³⁺) in the near and middle infrared spectral ranges. The emission, excitation, and absorption spectra, as well as the kinetic parameters, were measured over a broad temperature range. The crystal doping was produced by growing from the melt. No significant differences were found between the luminescence properties in bulk crystals and in fibers. The Judd-Ofelt analysis was applied to the doped crystals, and the transition rates, branching ratios, and quantum efficiencies were calculated. Good agreement was obtained between theory and experiment. The strong middle-infrared luminescence and the kinetic parameters of these crystals make them good candidates for the fabrication of fiber lasers in the 4-5.5μm spectral range.