Micron sized phosphors have been widely studied by using a solid-state reaction method for application in near UV-emitting LEDs. This method produces large crystallite size powders, but have higher quantum efficiencies than smaller crystallite size powders. For the phosphor configuration, the packing density of these large particles on the device is thus low and generates substantial light-scattering. To overcome this issue, phosphors with a small, narrow size distribution are required. If the particle radii are < ~400 nm, scattering from these particles will be negligible on visible and UV radiation. However, submicron-sized phosphors with nano-sized crystallites have poor quantum efficiency compared to micron-sized phosphors with micron-sized crystallites.

An addition of flux (NH₄F, NH₄Cl, or H₃BO₃) to the CaMgSi₂O₆:Eu²⁺ phosphors during synthesis was performed and the effect of the flux on the crystallite size and quantum efficiency of nanocrystalline and submicron phosphors particles was examined. The use of NH₄F or NH₄Cl increased the crystallite size in the submicron sized particles, which yielded an increase in emission intensity and quantum efficiency. Adding the H₃BO₃ flux crystallized SiO₂ and changed lattice parameters, degrading the luminescent properties. Excessive NH₄Cl was also examined and it resulted in nucleation of a second phase and changed lattice parameters with no improvement in luminescent properties. These results demonstrate that a careful selection and use of a flux is a method to improve the quantum efficiency of submicron particles sized phosphors. This work is supported by the National Science Foundation, Ceramics Program Grant (DMR-1411192).