Evaluating mid-IR laser potential of Er³⁺ vs. Dy³⁺ in low-maximum-phonon-energy hosts for 4.1-4.8 µm applications

A comparative spectroscopic investigation was conducted to evaluate the potential of Dy 3+ and Er 3+ doped Ga 2 Ge 5 S 13 chalcogenide glass and CsCdCl3 crystal for suitability as gain media for mid-infrared lasers operating within the 4.1-4.8 (m spectral range. Both rare-earth ions exhibited broad mid-IR emissions at room temperature centered at ∼4.4-4.5 µm, attributed to the Dy 3+ : 6 H 11/2 → 6 H 13/2 and Er 3+ : 4 I 9/2 → 4 I 11/2 transitions. The fluorescence lifetimes of these mid-IR transitions varied significantly between these two host materials. Dy 3+ and Er 3+ doped CsCdCl 3 crystals exhibited long lifetimes of ∼9-12 ms, while the same ions in Ga 2 Ge 5 S 13 glass yielded lifetimes in the range of ∼1 ms. Temperature-dependent lifetime measurements further confirmed the role of multiphonon relaxation in Dy 3+ : Ga 2 Ge 5 S 13 , although fitting with the temperature dependence of the multiphonon energy-gap law indicated the presence of additional nonradiative decay channels, likely involving impurity interactions. In contrast, Er 3+ emissions exhibited minimal temperature dependence across both hosts, with measured lifetimes closely matching calculated radiative values. Judd-Ofelt analyses revealed radiative properties and transition probabilities comparable to other low-maximum-phonon-energy rare-earth-doped hosts, with the studied Dy 3+ doped host materials standing out by offering sigma-tau products several times higher than those of Er 3+ in the same hosts.