Achieving Efficient Red-Emitting Sr₂Ca_1−δLn_δWO₆:Mn⁴⁺ (Ln = La, Gd, Y, Lu, δ = 0.10) Phosphors with Extraordinary Luminescence Thermal Stability for Potential UV-LEDs Application via Facile Ion Substitution in Luminescence-Ignorable Sr₂CaWO₆:Mn⁴⁺

In this work, we adopt a facile rare earth ions Ln3+ (Ln = La, Gd, Y, Lu) substitution strategy to achieve the efficient red luminescence Sr2Ca1−δLnδWO6:Mn4+ (δ = 0.10), which extremely improves the luminescence properties of luminescence-ignorable Sr2CaWO6:Mn4+. It is demonstrated that the substitution of Ln3+ for Ca2+ can stabilize the Mn in tetravalent state, which would like to occupy W6+ site and generate the luminescence. It is also found that the emission profile of original Sr2CaWO6:Mn4+ changes manifestly after different Ln3+ ions substitution, which is mainly attributed to the synergistic effect of lattice distortion, Mn4+ transition 2Eg → 4A2g and lattice vibration. Most fascinatingly, the Sr2Ca0.9Ln0.1WO6:0.005Mn4+ (SC0.9Ln0.1WO:0.005Mn4+, Ln = La, Gd) show extraordinary luminescence thermal stability, whose integrated emission intensity still maintains about 95% (Gd, 96.8%; La, 94.8%) at 478 K of its original value at room temperature (298 K), much better than those in most reported Mn4+-activated oxide phosphors so far. It is confirmed that the traps may play an important role for this phenomenon. Best of all, this work gives us a facile strategy to achieve efficient Mn4+-activated red-emitting materials with extraordinary luminescence thermal stabilities derived from luminescence-ignorable ones.