Synthesis and thermal, optical and magnetic properties of new Mn2+-doped and Eu3+-co-doped scheelites

A series of Mn2+-doped and Eu3+-co-doped calcium molybdato-tungstates, i.e., Ca1−3x−yMny⌷xEu2x(MoO4)1−3x(WO4)3x (0 < x ≤ 0.2222 when y = 0.0200 and 0 < y ≤ 0.0667 when x = 0.1667, ⌷ represents vacancy) materials were successfully synthesized via high-temperature annealing. XRD results confirmed the formation of single, tetragonal scheelite-type phases (space group I41/a). A change in both lattice constants (a and c), lattice parameter ratio c/a and progressive deformation of MoO4/WO4 tetrahedra with increasing Eu3+ as well as Mn2+ contents were observed. The melting point of doped materials is lower than the melting point of pure matrix, i.e., CaMoO4. New materials exhibit strong absorption in the UV range. They are insulators with the optical direct band gap (Eg) higher than 3.50 eV. The Eg values nonlinearly change with increasing dopants concentrations. EPR measurements allowed to establish the nature of magnetic interactions among Mn2+ ions. Additionally, EPR spectra were sensitive on both parameters: Mn2+ and Eu3+ concentration.