Intense NIR-II luminescence through stabilization of tetrahedral (Mn5+O4) lumophore in apatites with high external quantum efficiency

The discovery of highly efficient near-infrared (NIR) emitting phosphors is essential for multiple spectroscopic applications. Pentavalent-manganese (Mn5+) is a rarely-reported NIR-II activator due to the its instability in inorganic solids. In this study, Mn5+-activated apatite phosphors A5(B1-xO4)3X: xMn5+ (A = Sr, Ba; B = P, V; X = OH, F, Cl, Br) were reported. Benefiting from the discrete P/VO4 tetrahedron and stabilization effect of alkaline-earth cation, Mn5+ existed as MnO43− anion can be effectively incorporated into the A5(P/VO4)3X. A selection of 16 different apatites is conducted to test the structural and compositional effect on Mn5+ stabilization and luminescence. The structure-property relationship was discussed with a detailed analysis on Mn5+ Tanabe-Sugano diagram and Dq/B calculation. Particularly, the optimized Ba5(VO4)3Cl: 0.01Mn5+ (λex = 650 nm, λem = 1181 nm) reveals an exceptional external quantum efficiency of 61.1 % with vivid turquoise body color. The multiparametric thermometry by luminescence intensity ratio (LIR) and 1E lifetime were demonstrated with excellent linear regressions (R2 > 99.9 %) and high relative sensitivities of > 1.0% K−1 in the range of physiological temperatures. A NIR-II phosphor-converted light-emitting diode (pc-LED) is fabricated with a NIR output power of 30.18 mW at 60 mA driven current and photoelectric conversion efficiency of 6.63 %.