Insights into luminescence thermal quenching of Mn⁴⁺-doped BaLa(Na/Li)(W/Te)O₆ double perovskite red phosphors

Mn⁴⁺ activated red-emitting luminescent materials often suffer from severe temperature quenching. To get insight into the nature of this process and achieve a better thermal stability, a series of BaLa(Na/Li)WO₆:Mn⁴⁺ and BaLaLi(W/Te)O₆:Mn⁴⁺ far-red emitting luminescent materials have been synthesized using a traditional high-temperature solid-state reaction approach. The samples have been thoroughly characterized by means of XRD, SEM, temperature-dependent photoluminescence spectroscopy and decay kinetics measurements. It is shown that substitution reactions of Na⁺ and W⁶⁺ by Li⁺ and Te⁶⁺, respectively, increase the energy gap between ²E_g and ⁴T_2g states of Mn⁴⁺ due to the blue shift of the Mn^{4+ 4}T_2g excitation band, resulting in noticeable improvement of the thermal stability. The potential mechanism responsible for this observation is proposed. The work demonstrates an effective approach for optimizing luminescence thermal stability of Mn⁴⁺-doped inorganic oxide phosphors.