Double perovskite A₂LaNbO₆:Mn⁴⁺,Eu³⁺ (A = Ba, Ca) phosphors: potential applications in optical temperature sensing

Recently, much attention has been paid to Mn⁴⁺-doped phosphors due to their strong deep-red emissions which are in demand in white light-emitting diodes. However, a key challenge for the commercialization of Mn⁴⁺-doped phosphors is their low thermal stability caused by the thermal quenching of Mn⁴⁺ luminescence. Herein, a strategy of optical temperature sensing has been developed by specifically utilizing thermal quenching to explore the potential applications of Mn⁴⁺-doped phosphors in optical temperature sensing. In this work, we report two kinds of double perovskite type phosphors, Ba₂LaNbO₆ (BLN) and Ca₂LaNbO₆ (CLN), co-doped with Mn⁴⁺ and Eu³⁺. Through the study of temperature-dependent spectra in a large temperature range of 298-498 K, Mn⁴⁺ and Eu³⁺ yield different trends where the fluorescence intensity of Mn⁴⁺ ions decreases much more rapidly compared to that of Eu³⁺ ions as the temperature increases. Accordingly, based on the fluorescence intensity ratio (FIR) of the luminescence of Mn⁴⁺ and Eu³⁺, the optimal relative sensitivity of temperature sensing in the BLN and CLN matrices could reach 2.08% K^-1 and 1.51% K^-1, respectively. Finally, the application potential of Mn⁴⁺-doped phosphors in temperature sensing is confirmed by analyzing different temperature sensing results in the two matrices.