A comparative study on the mid-infrared fluorescence properties of Dy³⁺doped fluoride and sulfide crystals with low phonon energy

The effect of phonon energy on the mid-infrared spectral performance of Dy3+ is investigated in Dy(Gd):CaF2, Dy:LaF3, and Dy:PbGa2S4 crystals through room temperature and temperature-dependent spectroscopic studies. A relationship between the number of phonons (p) required for non-radiative quenching and the spectral properties is observed. Remarkably, the spectral parameters related to the Dy3+ 4.3 mu m emission exhibit significant changes by orders of magnitude around p = 6. This pattern deviates from the normal rule where the critical point is expected to be near p = 5. Overall, the 4.3 mu m mid-infrared luminescence of Dy3+ requires the phonon energy of the matrix to satisfy p > 6. This condition is more restrictive than that of mid-infrared luminescence in other rare earth ions such as Er3+ and Ho3+. This finding provides valuable guidance for the advancement of Dy3+ 4.3 mu m laser.