Frequency Upconversion Fluorescence Emission of Er³⁺-Doped Oxychloride Germanate Glass

Frequency upconversion fluorescence property of Er³⁺-doped oxychloride germanate glass is investigated. Intense green and red emissions centred at 525, 546, and 657nm, corresponding to the transitions ²H_11/2 → ⁴I_15/2, ⁴S_3/2→ ⁴I_15/2, and ⁴F_9/2→ ⁴I_15/2, respectively, were simultaneously observed at room temperature. The quadratic dependence of the 525, 546, and 657nm emissions on excitation power indicates that a two-photon absorption process occurs under 975nm laser diode (LD) excitation. The Raman spectrum investigation indicates that oxychloride germanate glass has the maximum phonon energy at ～805cm°C. The thermal stability of this oxychloride germanate glass is evaluated by differential scanning calorimetry, and thermal stability factor ΔT(ΔT = T_x-T_g) is 187°C. Intense upconversion luminescence and good thermal stability indicate that Er³⁺-doped oxychloride germanate glass is a promising upconversion laser material.