New wolframite-type micromaterials doped with Fe3+- and f-electron metal ions

Novel Zn1-3(x+y)▢x+yFe2xRE2yWO4, where RE = Ho3+, Er3+, Yb3+, x = 0.005, 0 < y ≤ 0.015, and ▢ represents vacancies in the crystal lattice. Solid solutions were successfully synthesized by the traditional solid-state reaction method using ZnO, Fe2O3, RE2O3 and WO3 as the initial reactants. Doped materials were extensively characterized by powder X-ray diffraction (XRD), differential thermal analysis-thermogravimetry (DTA-TG) methods, scanning electron microscopy (SEM–EDX), infrared (FT–IR), and ultraviolet–visible–near infrared (UV–vis–NIR) spectroscopies. The results revealed that all doped samples were phase pure with grain sizes practically not exceeding 10 µm, exhibiting uniform morphology. New materials belong to the wolframite-type structure with space group P2/c. Furthermore, activated by Fe3+ and RE3+ ions materials also demonstrated high thermal stability up to max. 1180 °C. They exhibit strong absorption in the ultraviolet range, and some of them (RE = Ho3+ and Er3+) also in the visible light. A detailed analysis of the UV–Vis–NIR spectra revealed that doped zinc tungstates possessed a direct optical band gap whose value is close to 3 eV. All these features make the new doped wolframite-type solid solutions promising candidates for multifield applications.