Defect–luminescence correlation in Lu₂SiO₅: Yb³⁺/Er³⁺nanophosphors

Temperature-sensitive phosphors based on the fluorescence intensity ratio (FIR) offer reliable non-contact thermometry for harsh environments. Lutetium oxyorthosilicate (Lu₂SiO₅, LSO) nanophosphors co-doped with Yb³⁺/Er³⁺were synthesized via a sol–gel route and annealed at 1000–1200 °C. A single B-type LSO phase, typically stable above 1150 °C, was achieved even at 1000 °C, with crystallite sizes of 20–50 nm. Under 975 nm excitation, strong green (510–575 nm) and red (625–700 nm) upconversion emissions were observed. FIR-based thermometry from room temperature to 870 K yielded maximum absolute sensitivities of 0.58 × 10⁻² K⁻¹ at 500 K and 0.60 × 10⁻² K⁻¹ at 450 K for samples annealed at 1000 °C and 1200 °C, respectively. Positron annihilation lifetime spectroscopy (PALS) confirmed reduced defect density and enhanced crystallinity with increasing Er³⁺content and annealing temperature. The combined optical and PALS analyses reveal the critical role of dopant-induced structural evolution in optimizing upconversion and thermometric performance.