Structure of the fluorine states in cadmium molybdate host studied by the electronic band structure calculations of CdMoO4, CdMoO4:F and CdMoO3F2 crystals

The electronic structures of CdMoO4, CdMoO3F2 and the fluorine-doped CdMoO4:F crystals are calculated by the Full-Potential Linear Augmented Plane Wave method. The energy dispersion curves, partial densities of electronic states and spatial distributions of electronic densities are calculated and analyzed in comparison with published experimental data. Relaxation of the crystal structure around the FO impurity in cadmium molybdate is revealed in geometry-optimization calculations carried out for CdMoO4:F. It is found that CdMoO3F2 crystal is as a direct-gap material. The Cd d, F p and O p states electronic states form the top of the Valence band and mainly Mo d states form the bottom of the Conduction band of CdMoO3F2 and all these states are involved into the lowest-energy band-to-band electronic transitions. The low-energy shift of the main bands in intrinsic luminescence emission and excitation spectra of CdMoO3F2 with respect to CdMoO4 may be a consequence of the lower Eg value of the oxyfluoromolybdate. Calculations suggest more complex structure of the luminescence centers in CdMoO3F2 in comparison with CdMoO4.