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A comparative study was conducted to investigate the 3.9 µm mid-IR emission properties of Ho³⁺doped NaYF₄and CsCdCl₃crystals as well as Ho³⁺doped Ga₂Ge₅S₁₃glass. Following optical excitation at ∼890 nm, all the studied materials exhibited broad mid-IR emissions centered at ∼3.9 µm at room temperature. The mid-IR emission at 3.9 µm, originating from the⁵I₅→⁵I₆transition, showed long emission lifetime values of ∼16.5 ms and ∼1.61 ms for Ho³⁺doped CsCdCl₃crystal and Ga₂Ge₅S₁₃glass, respectively. Conversely, the Ho³⁺doped NaYF₄crystal exhibited a relatively short lifetime of ∼120 µs. Temperature dependent decay time measurements were performed for the⁵I₅excited state for all three samples. The results showed that the emission lifetimes of Ho³⁺:CsCdCl₃and Ho³⁺:Ga₂Ge₅S₁₃were nearly temperature independent over the range studied, while significant emission quenching of the⁵I₅level was observed in Ho³⁺:NaYF₄. The temperature dependence of the multi-phonon relaxation rate for 3.9 µm mid-IR emission in Ho³⁺:NaYF₄crystal was determined. The room temperature stimulated emission cross-sections for all three samples were calculated using the Füchtbauer-Landenburg equation. Furthermore, the results of Judd-Ofelt analysis are presented and discussed.

We present mid-IR spectroscopic characterization of the low-phonon chalcogenide glass, Ga₂Ge₅S₁₃(GGS) doped with Er³⁺ions. Under the excitation at ∼800 nm, Er³⁺:GGS exhibited broad mid-IR emission bands centered at ∼2.7, ∼3.5, and ∼4.5 µm at room temperature. The emission lifetime of the⁴I_9/2level of Er³⁺ions in GGS glass was found to be millisecond-long at room temperature. The measured fluorescence lifetimes were nearly independent of temperature, indicating negligibly small nonradiative decay rate for the⁴I_9/2state, as can be expected for a low-maximum-phonon energy host. The transition line-strengths, radiative lifetimes, fluorescence branching ratios were calculated by using the Judd-Ofelt method. The peak stimulated emission cross-section of the⁴I_9/2→⁴I_11/2transition of Er³⁺ion was determined to be ∼0.10×10⁻²⁰cm²at room temperature.