Design strategies for optical thermometers based on diverse luminescence thermal-response in Li2CaTa2O7:Ln3+ phosphors (Ln3+ = Pr3+, Er3+)

In this paper, the photoluminescence properties of Li₂CaTa₂O₇:Ln³⁺ (Ln³⁺ = Pr³⁺, Er³⁺) phosphors were investigated. Under the 450 nm blue light excitation, Li₂CaTa₂O₇:Pr³⁺ exhibits emission ranging from green to red, and its strong response to blue-light excitation facilitates easier integration into device encapsulation processes. Under 379 nm excitation, the emission spectra of Li₂CaTa₂O₇:Er³⁺ display characteristic peaks in both the green and near-infrared regions. As the temperature increases, the photoluminescence intensities of the emission peaks at 533 nm (Pr³⁺) and 528 nm (Er³⁺) show a slight enhancement. Based on the distinct temperature dependencies of the thermally coupled levels of Pr³⁺ and Er³⁺, the relative sensitivity (S_r) and absolute sensitivity (S_a) of the samples were calculated using the fluorescence intensity ratio (FIR) method. The maximum S_r values for Pr³⁺ and Er³⁺ in the Li₂CaTa₂O₇ host were found to be 3.072 % K⁻¹ at 120 K and 7.739 % K⁻¹ at 140 K, respectively. These results demonstrate the excellent thermometric performance of Li₂CaTa₂O₇:Ln³⁺ (Ln³⁺ = Pr³⁺, Er³⁺), highlighting its potential for temperature sensing applications.