Effect of sintering atmosphere and lithium ion co-doping on photoluminescence properties of NaCaPO4:Eu2+ phosphor

This paper reports on the photoluminescence properties of Na1−yLiyCa1−xPO4:xEu2+ phosphors synthesized by a solid state reaction method. The prepared phosphors have been thoroughly characterized by means of X-ray diffraction (XRD), Field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectrum (FTIR), Raman spectrum, Thermo gravimetric and differential thermal analysis (TG–DTA) and photoluminescent spectral measurements. The structure of Na1−yLiyCa1−xPO4:xEu2+ phosphors were found to be orthorhombic in nature with a sphere-like morphology and having the particle size in micrometer range. The excitation spectra of NaCaPO4:Eu2+ phosphors revealed a broad excitation band having its maximum intensity at 373 nm and ranging from 250 m to 450 nm. Incidentally, it matches well with the ultraviolet (UV) radiation of light-emitting diodes (LEDs). Upon 373 nm excitation, these phosphors exhibited intense bluish-green emission band centered at 505 nm. The effect of sintering atmospheres and co-doping of lithium ions on the photoluminescence properties of the NaCaPO4:Eu2+ phosphors were studied and explained suitably. The obtained results indicate that the prepared NaCaPO4:Eu2+ phosphors are promising bluish-green candidates for the phosphor-converted white LED applications.