Partial Substitution of Er and V or Er and Nb into the CaWO₄ Scheelite

We successfully synthesized the erbium (Er)-doped optical material calcium tungstate (CaWO₄) while maintaining charge balance by codoping Er with vanadium (V⁵⁺) and niobium (Nb⁵⁺) into the optical material calcium tungstate (CaWO₄). The synthesized samples, with the general formula Ca_{1- x} Er_x W_{1- x} M_x O₄ (M = V or Nb), were annealed at 1200 °C in air. Er³⁺ dopants introduced localized visible-light transition states within the band gap, thus adding pink hues to the white CaWO₄ for both codoping systems. Phase-pure materials were obtained up to the doping levels of x = 0.10, beyond which impurity peaks in powder X-ray diffraction patterns emerged. Reduction in lattice constants and grain sizes due to dopant substitution was observed. No evidence was seen for long-range magnetic ordering above 0.5 K, and the local crystal field of Er³⁺ was different for the two codopants. Charge-compensated codoping is thus shown to be an effective strategy for tailoring scheelite optical properties.