Achieving high sensing sensitivity in a Dy³⁺ doped garnet phosphor toward optical thermometry

Optical thermometers have garnered significant attention, and there has been a rapid development of high-performance optical thermometers. However, achieving high sensing sensitivity phosphor materials is still a significant challenge. In this study, a Dy³⁺ doped garnet Ca_2.5Hf_2.5Ga₃O₁₂ (CHGO) phosphor with high sensing sensitivity is reported. Characteristic blue emissions originating from the thermally coupled energy levels of ⁴I_15/2 and ⁴F_9/2 to the ⁶H_15/2 ground level of Dy³⁺ ions were investigated, observing opposite temperature dependent emission behavior. The fluorescence intensity ratio (FIR) approach was utilized to investigate the optical temperature sensing properties of CHGO:Dy³⁺ phosphors based on the different thermal quenching transitions of the thermally coupled energy levels (⁴I_15/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_15/2). Under 352 nm light excitation, CHGO:Dy³⁺ exhibits the maximum absolute and relative sensitivities of 0.13% K⁻¹ at 523 K and 2.12% K⁻¹ at 298 K, respectively, demonstrating high performance temperature sensing, high sensitivity, excellent repeatability and reusability. Finally, a simple optical temperature sensing strategy was proposed to investigate the optical thermometry performance of CHGO:Dy³⁺ phosphors, indicating their great optical thermometry behavior for optical thermometric applications. This study focusing on the optical temperature sensing of CHGO:Dy³⁺ phosphors lays a robust foundation and constitutes a valuable resource for future investigations delving into the realm of temperature sensing capabilities of Dy³⁺-doped phosphors.