Optical Properties of Eu2(WO4)3 and Tb2(WO4)3 and of CaWO4 Doped with Eu3+ or Tb3+ - Revisited

The optical properties of CaWO4 doped with Eu3+ or Tb3+, Eu-2(WO4)(3) and Tb-2(WO4)(3) are studied for possible new applications as red and green phosphors efficiently converting long-wavelength UV light from nitride compound semiconductor light emitting diodes. Trivalent rare earth ions in the Ca2+ sites cause cation vacancies and severe distortion of tungstate tetrahedra around the vacancies. The 4f(n) intraconfigurational transitions of the Eu3+ and the Tb3+ ions are significantly enhanced in the distorted scheelite structures of CaWO4 (loped with Eu3+ or Tb3+, Eu-2(WO4)(3) and Tb-2(WO4)(3). The excitation spectra show strong f-f transition peaks of Eu3+ or Tb3+ in the long-wavelength UV region in addition to the charge transfer (O2- -> Eu3+) band for Eu3+ or the interconfigurational f -> d transition band for Tb3+ in the short-wavelength UV region.