Combustion synthesis and luminescence investigation of Na₃Al₂(PO₄)₃:RE (RE = Ce³⁺, Eu³⁺ and Mn²⁺) phosphor

Rare-earth (Ce³⁺or Eu³⁺) or alkali-earth metal (Mn²⁺) doped Na₃Al₂(PO₄)₃ phosphor powder were prepared by a combustion method. Regardless of the dopants, the Na₃Al₂(PO₄)₃ was shown to crystallize as hexagonal (rhombohedral) NASICON phase with spheroidal micron sized particles based upon X-ray diffraction (XRD) and scanning electron microscopy (SEM) data. As confirmed by thermogravimetric (TGA) and differential thermal analysis (DTA) data, the powders were stable at high temperatures up to 900 °C. A broad UV emission (with maximum at 328 nm) associated with the 5d → 4f transition of Ce³⁺ was observed from Na₃Al₂(PO₄)₃:Ce³⁺ while Mn²⁺ and Eu³⁺ doping showed stable green and red photoluminescence emission at 515 and 615 nm, respectively. For different molar concentrations of rare-earth/alkali-earth metal dopants, the PL intensity was shown to increase to a certain concentration before quenching occurred at higher concentrations. The structure and optical properties of these phosphors were evaluated.