Strong Red Upconversion Luminescence of LiYO ₂ : Er ³⁺ Phosphor for Optical Thermometry

Herein, LiYO 2 : Er 3+ phosphors were synthesized via a high‐temperature solid‐state reaction method. Under the excitation of a 980 nm laser, the phosphors exhibit strong green (563 nm, 4 S 3/2 → 4 I 15/2 ) and red (662 nm, 4 F 9/2 → 4 I 15/2 ) light upconversion emissions. Based on the upconversion luminescence spectra, the optimal doping concentration of Er 3+ ions in LiYO 2 was determined to be 0.03. In addition, the optical temperature sensing properties of the LiYO 2 : 0.03 Er 3+ phosphor were investigated using the nonthermally coupled method by analyzing the luminescence intensity ratio (LIR) (I 563 /I 662 ). The maximum relative sensitivity ( S R ) and absolute sensitivity ( S A ) reached 1.07% K −1 (at 473 K) and 0.01 K −1 (at 473 K), respectively. It shows excellent thermal sensitivity. This study highlights the significant potential of LiYO 2 : Er 3+ phosphors for applications in noncontact temperature sensing fields.