Integrating unwonted photoluminescence and anti-thermal quenching in Ba2MgTeO6 double perovskites for high-performance optical thermometers

Abstract

An unwonted photoluminescence dominating in the cyan region is discovered in Ba₂MgTeO₆ double perovskite. It originates from the ³T_2u, ³T_1u – ¹A_1g electronic transitions of Te⁴⁺ ions within Ba₂MgTeO₆ and possesses tunability from the cyan to NIR region. The cyan emission shows an anti-thermal quenching behaviour at low temperatures while a faster thermal quenching is observed above 300 K. Considering the extraordinary temperature dependence of inherent emission of Ba₂MgTeO₆, a novel Eu³⁺-activated Ba₂MgTeO₆ phosphor was developed for ratiometric temperature sensing. An unusual excitation-driven switching of maximum intensity from magnetic dipole transition to electric dipole transition due to the partial release of parity inhibition is also observed in Eu³⁺-activated Ba₂MgTeO₆. The temperature-dependent Raman and PL excitation studies reveal that the increased thermal population of vibrational levels causes a rapid thermal quenching of Te⁴⁺ luminescence via the cross-over point. Furthermore, a higher relative sensitivity of 3.16 and 4.86% K⁻¹ was obtained for the Ba₂MgTeO₆:0.02Eu³⁺ phosphor based on the FIR and EIR modes, respectively. This study will definitely provide new directions in the areas of solid-state lighting and optical thermometry.