Temperature sensing performance based on up-conversion luminescence in hydrothermally synthesized Yb³⁺/Er³⁺ co-doped NaScF₄ phosphors

Abstract

NaScF₄:Yb³⁺/Er³⁺ crystals were successfully hydrothermally synthesized using distilled water as a single solvent. The crystal phase and morphology were characterized by XRD and SEM. Compared with organic solvents such as ethanol, ethylene glycol and ether, the molar ratio of Na/F/Sc plays an important role in the synthesis of NaScF₄ crystals. Morphological control was achieved by changing the types of additives, and the relationship between morphology and luminescence properties was explored. The NaScF₄:Yb³⁺/Er³⁺ phosphors exhibit strong green and red UC emissions under the excitation of 980 nm NIR. Optimal concentrations of Yb³⁺ and Er³⁺ for up-conversion luminescence performance were identified as 10% and 2%, respectively. Without any subsequent heat treatment process, the obtained NaScF₄:10%Yb³⁺/2%Er³⁺ showed good temperature sensitivity. The temperature sensing ability was investigated by employing the dependence of the fluorescence intensity ratio (FIR) of the two thermal coupling energy levels of Er³⁺ (²H_11/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2) on temperature; the maximum sensitivity S_A/S_R was 0.00256 K^-1/0.00317 K^-1 at 548 K, and it increased to 0.00328 K^-1/0.00413 K^-1 after adding EDTA. In addition, an evaluation of temperature uncertainty during temperature measurement was performed, and was found to be 0.073 K and 0.095 K in the presence and absence of EDTA, respectively. Compared with some other reported materials, the obtained material shows a relatively superior temperature sensitivity, which provides new ideas for the improvement of temperature-sensitive materials.