Origin of luminescence in ZnMoO4 crystals: Insights from spectroscopic studies and electronic structure calculations

Abstract

Abstract A set of ZnMoO4 polycrystalline samples was synthesized by solid state reaction method and characterized by XRD structural analysis, ICP elemental analysis, SEM-EDX analysis, UV–Vis diffuse reflectance spectroscopy. The photoluminescence (PL) properties of ZnMoO4 samples were studied in 8–300 K temperature range with use of synchrotron radiation as an excitation source. The geometry-optimized electronic structure calculations of perfect and defective ZnMoO4 crystals were carried out by the DFT-based band-structure methods, plane-wave pseudo-potential (CASTEP program package) and FP-LAPW (Wien2k package). A number of point defects which can influence the luminescence properties of ZnMoO4 was considered in calculations, namely the oxygen vacancy Vo, compensated vacancies Vo + VZn, tungsten impurity WMo and the MoO3-deficient phase Zn3Mo2O9. Comparative analysis of experimental data and calculation results allowed explanation of the origin of the red and blue-green luminescence emission bands of ZnMoO4 as well as formation of their excitation spectra. It is assumed that the green component of ZnMoO4 luminescence emission, like in other molybdates of MIIMoO4 family (MII = Ca, Sr, Cd, Pb) originates from radiative annihilation of excitons self-trapped on regular MoO4 groups. The Red component of ZnMoO4 emission has a defect-related origin and it originates from radiative transitions in MoO4 groups located near oxygen vacancies.