Experimental optimization design for up-conversion luminescence properties and FIR based optical temperature sensing in BaGeTeO6: Er3+, Yb3+ fluorescent materials

Abstract

The regression equation correlating the doping concentration of Er³⁺/Yb³⁺ with luminescence intensity was established from a theoretical model, which was further refined through experimental optimization design. Then, the optimal solution of the equation was calculated by genetic algorithm, and the doping concentrations of Er³⁺ and Yb³⁺ were obtained to be 5.61 mol% and 33.55 mol% under 980 nm near-infrared radiation excitation, and 5.58 mol% and 28.88 mol% under 1550 nm near-infrared radiation excitation, respectively. Then, the Er³⁺/Yb³⁺ co-doped BaGeTeO₆ up-conversion phosphors powder was synthesized by high-temperature solid phase method. And the crystal structure of the resulting fluorescent powder was analysed by X-ray diffraction to confirm that the optimal BaGeTeO₆ samples were pure phase. The up-conversion fluorescence emission spectra of the samples were measured under 980 nm and 1550 nm pumping conditions, and strong green and red emissions were found with peaks at around 532 nm, 555 nm and 672 nm, corresponding to the jumps of the ²H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2 energy levels, respectively. For the optimal samples under these two pumping conditions, the relationship between the up-converted fluorescence and the laser operating current is explored.The up-converted fluorescence in these two cases is shown to be a two-photon and three-photon process, respectively, and the mechanism of the up-converted fluorescence is analysed and discussed in detail. In addition, the relationship between the up-conversion fluorescence and the temperature of the optimal samples is also investigated, revealing the excellent temperature sensing properties of the up-conversion emission under 980 nm and 1550 nm near-infrared radiation excitation.