The determining factor of the luminescence energies of vanadate phosphors

The molecular orbital calculations based on the DV-Xα method were carried out for several vanadate phosphors of Sr2VO4Cl, Ca2VO4Cl, Ba2V2O7, Mg3(VO4)2, and Zn3(VO4)2, of which the luminescent colors range from deep-blue to yellow through green. The structural refinement with the X-ray diffraction technique preceded the DV-Xα calculations to provide a theoretical interpretation on the relationship between the crystal structures and the luminescent colors (luminescence energies) of the vanadate phosphors. The partial density of states obtained in the DV-Xα calculations reasonably explained the lowest excitation energies of the vanadate phosphors. The calculations also exhibited the difference in the bonding characters among the ligand oxygens in a VO4 tetrahedron due to the structural distortion. The relatively large contributions of the ionically coordinated oxygens were proposed on determining the luminescence energies. A linear correlation was deduced between the luminescence energies and the averaged V–O distances with the selected oxygens ionically coordinated to V.