Site Preference-Driven Mn4+ Stabilization in Double Perovskite Phosphor Regulating Quantum Efficiency from Zero to Champion

The tetravalent-state stability of manganese is of primary importance for Mn4+ luminescence. Double perovskite-structured A(2)B'B '' O-6:Mn4+ has been recently prevalent, and the manganese ions are assumed to substitute for the B ''(IV-VI)O-6 site to stabilize at the tetravalent charge state to generate far-red emissions. However, some Mn-doped A(2)B'B '' O-6-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 2Ca(2+) 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 Mn 4 trelated 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.

Automated summary

By proposing a cation-pair co-substitution strategy, a novel Mn4+-activated red phosphor has been successfully designed, which significantly enhances the effective Mn4+/Mn2+ concentration while achieving highly efficient far-red emission.