Structural and Upconversion Fluorescence Properties of Er³⁺/Yb³⁺-Codoped Lead-Free Germanium-Bismuth Glass

We study the structural and infrared-to-visible upconversion fluorescence properties of Er³⁺/Yb³⁺-codoped lead-free germanium-bismuth glass. The structure of lead-free germanium-bismuth-lanthanum glass is investigated by peak-deconvolution of Raman spectroscopy. 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, are 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 excitation.