Direct mechanochemical synthesis of SrMoO4: structural and luminescence properties

In this study, the effects of ball milling conditions on the phase formation, symmetry of structural units and photoluminescence features of SrMoO₄ were investigated. A stoichiometric mixture of SrCO₃ and MoO₃ in a molar ratio of 1 : 1 was subjected to intense mechanical treatment in air using a planetary ball mill by applying two milling speeds: 500 and 850 rpm. The obtained samples were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), Raman spectroscopy, infrared (IR) spectroscopy, UV-vis (UV-vis) diffuse reflectance spectroscopy and photoluminescence (PL) spectroscopy. The fast synthesis (1 h milling time) of tetragonal SrMoO₄ occurred at the higher milling speed of 850 rpm. A longer milling time (5 h) was needed to synthesize SrMoO₄ at a lower milling speed of 500 rpm. The average crystallite sizes of the as-prepared samples were 25 and 20 nm at 500 and 850 rpm, respectively. SEM analysis revealed that the mechanochemically produced SrMoO₄ sample contained a variety of particle shapes including hexagonal and polyhedral ones. Raman and IR spectroscopy results confirmed the formation of tetragonal SrMoO₄. UV-vis absorption spectra showed one peak at 230 nm, and the calculated optical band gaps of SrMoO₄ were 4.27 eV (5 h/500 rpm) and 4.34 eV (1 h/850 rpm). Photoluminescence (PL) spectra of both the samples exhibited blue emissions with a peak maximum at 400 (405) nm upon excitation at 325 nm wavelength. CIE coordinates of this mechanochemically synthesized SrMoO₄ were located in the blue region with different positions.