UV-Blue Upconverted Emission from Nd³⁺-Doped InF₃-Based Heavy-Metal Fluoride Glasses for Blue Upconversion Fibre Laser

We report spectral properties and thermal stability of Nd³⁺-doped InF₃-based heavy-metal fluoride glasses. Fluoroindate glasses in the chemical compositions (in mol%) of (38-x)InF₃-16BaF₂-20ZnF₂-20SrF₂-3GdF₃-1GaF₃-2NaF- xNdF₃ (x= 0.1, 0.5, 1, 2, 3) have been prepared under a controlled atmosphere in a dry box. Strong UV--blue upconversion emission from a green excitation wavelength has been observed and the involved mechanisms have been explained. Near-infrared emission occurs simultaneously upon excitation of the UV--blue upconversion emissions with a cw Ar⁺ laser. The upconversion spectra have revealed four dominant emissions at 354, 380, 412 and 449nm, which belong to the transitions of ⁴_3/2 → ⁴I_9/2, ⁴D_3/2 → ⁴I_11/2 and ²P_3/2 → ⁴I_9/2,⁴D_3/2 → ⁴I_13/2 and ²P_3/2 → ⁴I_11/2, ⁴D_3/2 → ⁴I_15/2 and ²P_3/2 → ⁴I_13/2, respectively.