Excellent optical thermometry based on single-color fluorescence in spherical NaEuF₄ phosphor

Temperature-dependent luminescence of spherical NaEuF₄ phosphors with different particle sizes was studied. The thermally coupled ⁵D₀ and ⁵D₁ level of Eu³⁺ was observed. The linear dependence of emission intensities of ⁵D₀ level of NaEuF₄ phosphor on temperature confirmed the excellent temperature sensing performance. Sensitivity up to 0.43% is achieved via decreasing the particle size, which is higher than that of reported thermometry based on upconversion of lanthanide ions. Moreover, the original luminescent intensity of 90% was recovered after 10 temperature-changed cycles, indicating good sensing stability. Therefore, spherical NaEuF₄ phosphor might be a promising candidate for optical temperature sensors.