Upconversion luminescence and energy transfer of GdAlO3:Yb3+,RE3+ (RE=Ho, Er, Tm) phosphors for optical temperature sensing

Rare-earth-doped upconversion materials play a crucial role in the development of temperature sensing based on fluorescence intensity ratio (FIR). In this work, the upconversion (UC) luminescence of GdAlO 3 (GAP):Yb 3+ ,RE 3+ (RE = Ho, Er, Tm) phosphors was investigated. Under 980 nm laser excitation, GAP:Yb 3+ ,Ho 3+ emitted green ( 5 F 4 , 5 S 2 → 5 I 8 ) and red ( 5 F 5 → 5 I 8 , 5 F 4 → 5 I 7 ) light, GAP:Yb 3+ ,Er 3+ emitted green ( 2 H 11/2 , 4 S 3/2  →  4 I 15/2 ) and red ( 4 F 9/2  →  4 I 15/2 ) light, GAP:Yb 3+ ,Tm 3+ emitted blue ( 1 G 4 → 3 H 6 ) and red ( 1 G 4 → 3 F 4 , 3 F 3 → 3 H 6 ) light. Within the temperature range of 260–500 K, GAP:Yb 3+ ,Ho 3+ exhibits a maximum absolute sensitivity ( S a ) of 0.0078 K −1  at 460 K and a maximum relative sensitivity ( S r ) of 1.391% K −1 at 300 K, corresponding to the non-thermally coupled levels (NTCLs) 5 S 2 / 5 F 5 . Meanwhile, GAP: Yb 3+ ,Er 3+ shows a maximum S a of 0.00367 K −1  at 500 K and a maximum S r of 1.562% K −1 at 260 K, associated with the thermally coupled levels (TCLs) 2 H 11/2 / 4 S 3/2 . Remarkably, the maximum S a and S r of GAP:Yb 3+ ,Tm 3+ reached 0.03576 K −1  at 500 K and 6.740% K −1 at 260 K for NTCLs 1 G 4 / 3 F 3 . These results demonstrate significant potential for applications in high-sensitivity thermal sensing and non-contact optical thermometry.