Host excitation and luminescence in large band gap oxides

A good understanding of the electronic states near the band gap of large gap materials is essential for designing phosphors when the energy of exciting radiation exceeds the band gap. This is particularly true when phosphors are designed for application in rare gas discharges with vacuum UV (VUV) radiation. Using density functional ab initio methods (augmented spherical waves and full potential linear muffin-tin orbitals), we have analyzed the nature of host excitations near the band gap energy for a number of complex oxides: LaPO4, AlPO4, BaB2O4, YBO3 and LuBO3 and the common trends in the optical transitions in berates and phosphates and the corresponding binary oxides La2O3, Lu2O3, Y2O3, BaO, B2O3 and P2O5 We have also studied the nature of impurity states of Eu3+ and Pr3+ substituting Y3+ in large gap oxides. The studies show how the relative ordering of the one-electron states of activator ions with respect to band states of the host lattice may affect their luminescence properties under host excitation.