Effect of co-doping alkali metal ions Li+/Na+/K+ on the photoluminescence enhancement properties of the near white light emitting LiSrVO4:Dy3+ phosphor along with the optical transition probabilities by Judd-Ofelt analysis for WLEDs application

Cool white light emitting LiSr1-xVO4:xDy3+ and LiSr1-x-yVO4:xDy3+, yM+ (M+ = Li+/Na+/K+) vanadate phosphors were synthesized by a conventional solid state reaction method. Powder X-ray Diffraction revealed the crystallinity and the phase formation. The morphology, agglomeration, elemental composition and the mapping of elements were analyzed using the Scanning Electron Microscopy and the EDAX mapping studies. The band gap and the refractive index of the prepared phosphors were determined through the diffuse reflectance spectroscopy. The photoluminescence excitation and the emission spectra were investigated. Under the 316 nm excitation, the luminescence spectrum showed emission peaks at 480 nm (blue), 570 nm (yellow) and 664 nm (red). The absorption spectrum was used to calculate the Judd -Ofelt parameters. These parameters were employed to investigate the different radiative properties. Influence of the charge compensators (alkali metal ions) on the PL properties were analyzed. Excellent thermal stability of 83% was obtained for this phosphor with the activation energy of 0.20 eV. The electric dipole transition influenced this phosphor to emit a broad yellow emission band. The Commission Internationale de I'Éclairage (CIE) coordinates were found from the emission spectrum, and its (x, y) values were (0.307, 0.361), with a correlated color temperature of 6568 K and a color purity of 5%. Additionally, the prepared vanadate phosphor is appropriate for near UV (NUV) excitable white LED applications.