Optical Properties of LaF₃–LaOF:Yb³⁺/Tm³⁺ Upconversion Phosphors: Influence of Annealing Temperature and Time

In this study, LaF₃–LaOF:Yb³⁺/Tm³⁺ upconversion phosphors were synthesized using a solid-state reaction method, and the effects of annealing conditions on their crystal structure and optical properties were examined. The crystal structure, analyzed using an X-ray diffractometer, revealed a transition from LaF₃ to LaOF as the annealing temperature and time increased. The photoluminescence (PL) characteristics revealed emission peaks at wavelengths of 477, 485, 795, and 803 nm. In addition, the PL intensity increased under annealing conditions of 1150℃ for 1–3 h. The pump-power dependence of the PL intensity suggested potential thermal quenching. Finally, the temperature characteristics were analyzed, yielding an absolute sensitivity of 0.0081 K⁻¹ and a relative sensitivity of 0.65% K⁻¹.