Site Preference-Driven Mn<sup>4+</sup> Stabilization in Double Perovskite Phosphor Regulating Quantum Efficiency from Zero to Champion
Yufei Wang, Fan Ding, Jiayu Wu, Jingbo Ke, Xiaoze Yuan, Xiaofang Wang, Zhongxian Qiu, Wenli Zhou, Jilin Zhang, Shixun Lian
Abstract
The tetravalent-state stability of manganese is of primary importance for Mn4+ luminescence. Double perovskite-structured A2B′B″O6:Mn4+ has been recently prevalent, and the manganese ions are assumed to substitute for the B″(IV–VI)O6 site to stabilize at the tetravalent charge state to generate far-red emissions. However, some Mn-doped A2B′B″O6-type materials show no or weak luminescence such as typical Ca2MgWO6:Mn. In this work, a cation-pair co-substitution strategy is proposed to replace 2Ca2+ by Na+–La3+ to form Ca2–2xNaxLaxMgWO6:Mn. The significant structural distortion appears in the solid solution lattices with the contraction of [MgO6] but enlargement of [WO6] octahedron. We hypothesize that the site occupancy preference of Mn migrates from Mg2+ to W6+ sites. As a result, the effective Mn4+/Mn2+ concentration enhances remarkably to regulate nonluminescence to highly efficient Mn4+-related far-red emission. The optimal CaNa0.5La0.5MgWO6:0.9%Mn4+ shows an internal quantum efficiency of 94% and external quantum efficiency of 82%, reaching up to the top values in Mn4+-doped oxide phosphors. This work may provide a new perspective for the rational design of Mn4+-activated red phosphors, primarily considering the site occupancy modification and tetravalent-state stability of Mn.