Influence of peculiarities of electronic excitation relaxation on luminescent properties of MgWO4

Resumo

Luminescent properties of magnesium tungstate monocrystals grown by two different methods are studied. Only the exciton luminescence of these crystals themselves is observed. Temperature dependence of the low-energy range in the luminescence excitation spectra is described by the Urbach rule. Slope coefficient σ₀ = 0.74 obtained from this dependence implies autolocalization of the excitons in MgWO₄. The processes of electronic excitations relaxation are considered depending on the structure of valence band in MgWO₄ and in other wolframites, ZnWO₄ and CdWO₄. In contrast to ZnWO₄ and CdWO₄, the d-states of the cation do not participate in formation of the MgWO₄ valence band. Using the excitation spectra measured in the range of the fundamental absorption (4–20 eV), it is shown that this difference manifests itself in relaxation of electronic excitations and may be the cause of the relatively low light yield of MgWO₄.