Blue shift in optical emission spectra of ZnGa2O4 by lattice deformation due to Eu atom amount in spinel lattice

We investigated the structural and electronic energy configurations of the spinel oxide ZnGa2O4 lattice according to the crystal-phase fractions originating from substituted Eu atoms. Rietveld refinements were employed to determine the crystal structure of Eu-doped ZnGa2O4. Rietveld refinements were based on assumption of simultaneously formed three crystal phases in the normal spinel ZnGa2O4. Pure ZnGa2O4, ZnGa2O4 with Eu atoms in tetrahedral sites, and ZnGa2O4 with Eu atoms in octahedral sites were the proposed phases randomly distributed through all spinel structure. Eu atom positions in the spinel lattice were readjusted the "a" parameters from 8.3363 +/- 0001 angstrom (for pure ZnGa2O4) to 8.3227 +/- 0001 angstrom (for Eu atoms in tetrahedral sides) and 8.3393 +/- 0001 angstrom (for Eu atoms in octahedral sites). Furthermore, the consequences of replacement of Eu+3 ions in octahedral side and Eu+2 ions in tetrahedral side were monitored by lowering optical emission intensity and blue shift at optical emission spectra. The blue shift was indicated by an increase in the band gap values from 4.69 +/- 0.01 eV to 4.92 +/- 0.01 eV.