A.E. Savon

Electronic structure and luminescence mechanisms in ZnMoO4 crystals.

Calculations of the band structure, partial densities of states and optical spectra of permittivity, reflectivity and absorption of perfect ZnMoO(4) crystal were performed using the full-potential linear-augmented-plane-wave method. It is shown that the calculated reflectivity spectra reproduce the main features of corresponding experimental spectra in the fundamental absorption region. The bandgap value of ZnMoO(4) is estimated as E(g) = 4.3 eV. Peculiarities of luminescence excitation spectra corrected for near-surface losses and losses on reflectivity are discussed, taking into account the results of the calculations. It is found that the energy structure of the lower part of conduction band is manifested in the excitation spectra of the intrinsic luminescence. The excitation spectra in the region 4.3-8.0 eV are formed by band-to-band electronic transitions mainly within the molybdate groups MoO(4)(2-), whereas electronic states of Zn(2+) cations are not directly involved into the excitation processes. It is shown that the structure of the intrinsic luminescence excitation spectrum depends on the temperature and mechanisms of the structure modification are discussed.

Numerical simulation of energy relaxation processes in a ZnMoO4 single crystal

We present the results of our experimental investigation and numerical simulation of excitation-energy relaxation processes in zinc molybdate crystals. We show that our kinetic model of the energy relaxation makes it possible to describe basic features of experimental results. Using this model, we estimate the trap concentration in ZnMoO4 upon irradiation of the crystal by VUV synchrotron radiation and X-ray radiation. We conclude that prolonged phosphorescence of ZnMoO4 that is observed after irradiation of the crystal by X-ray radiation can be caused by the occurrence of additional traps with a low activation energy.