Temperature dependence of middle infrared absorption lines in silver halide crystals doped with Pr³⁺, Dy³⁺, and Nd³⁺ ions

The electron-phonon coupling was investigated for mid-infrared transitions in silver halide crystals doped with Pr, Dy, or Nd. The temperature dependence of the absorption spectral line widths and the line shifts were measured in mid-infrared absorption lines in these crystals. It was shown that in each case the temperature dependence is consistent with the two-phonon Raman process model having a single characteristic Debye temperature. This Debye temperature was found to be in the range of 142-155.5 K. It was also found that below 50 K the line widths are caused by inhomogeneous crystal strains.