Temperature-dependent and threshold behavior of Sm3+ ions on fluorescence properties of lithium niobate (LiNbO₃, LN) single crystals were systematically investigated. The test materials, congruent LiNbO₃ single crystals (Sm:LN), with various concentrations of doped Sm3+ ions from 0.2 to 2.0 mol.%, were grown using the Czochralski technique. Absorption spectra were obtained at room temperature, and photoluminescence spectra were measured at various temperatures in the range from 73 K to 423 K. Judd⁻Ofelt theory was applied to calculate the intensity parameters Ωt (t = 2, 4, 6) for 1.0 mol.% Sm3+-doped LiNbO₃, as well as the radiative transition rate, Ar, branching ratio, β, and radiative lifetime, τr, of the fluorescent ⁴G5/2 level. Under 409 nm laser excitation, the photoluminescence spectra of the visible fluorescence of Sm3+ mainly contains 568, 610, and 651 nm emission spectra, corresponding to the energy level transitions of ⁴G5/2→⁶H5/2, ⁴G5/2→⁶H7/2, and ⁴G5/2→⁶H9/2, respectively. The concentration of Sm3+ ions has great impact on the fluorescence intensity. The luminescence intensity of Sm (1.0 mol.%):LN is about ten times as against Sm (0.2 mol.%):LN at 610 nm. The intensity of the fluorescence spectra were found to be highly depend on temperature, as well as the concentration of Sm3+ ions in LiNbO₃ single crystals, as predicted; however, the lifetime changed little with the temperature, indicating that the temperature has little effect on it, in Sm:LN single crystals. Sm:LN single crystals, with orange-red emission spectra, can be used as the active material in new light sources, fluorescent display devices, UV-sensors, and visible lasers.
Keywords: J-O theory; fluorescence spectroscopy; lithium niobate; rare earth-doped materials; temperature; threshold concentration.