Monodisperse CaAl12O19:Mn4+ microspheres for full-spectrum white LEDs

Non-rare-earth Mn4+-activated red-emitting oxide phosphors have emerged as potential alternatives of typical Eu2+ doped nitrides owing to broad-band absorption, narrow-band emission, high color purity and low cost. In this work, highly efficient CaAl12O19:Mn4+ microspheres with uniform size distributions were first prepared by combining an epoxide-driven sol-gel method with heat treatment in oxygen atmosphere. The spherical morphology is beneficial to reduce scattering of light to enhance the photoluminescence of the phosphor. This phosphor shows red emission attributed to Mn4+: 2Eg → 4A2g spin-forbidden transition in the range of 600~750 nm under excitation at 340 nm. Partitioning Mg2+ in the host was found to enhance Mn4+ luminescence because of charge balance effect and the proposed mechanisms were discussed. The luminescence quantum yield of CaAl11.7576O19:0.0024Mn4+, 0.24Mg2+ microspheres which were heat treated for 4 h at 1300 °C was measured to be 56.1%. The white LED device based on the glass ceramic containing phosphors was found to show a high-color-rendering index of 96 and a low correlated color temperature of 4522 K. The results indicate that CaAl12O19:Mn4+ microspheres have great potential for near-ultraviolet LEDs on full-spectrum lighting.