Molten salt synthesis, visible and near-IR region spectral properties of europium or neodymium doped CoNb₂O₆ columbite niobate

Pure Nd³⁺- or Eu³⁺-doped CoNb₂O₆ powders have been prepared by a molten salt synthesis method using a Li₂SO₄-Na₂SO₄ or NaCl-KCl salt mixture as a flux at relatively low temperatures as compared to the solid state reaction method. X-ray diffraction patterns of pure CoNb₂O₆ samples indicated an orthorhombic single phase. For Eu³⁺-doped CoNb₂O₆ samples, the luminescence of Eu³⁺ was observed at 615 nm as red emission while the Nd³⁺ doped sample showed a typical emission at 1064 nm varying with the Eu³⁺ or Nd³⁺ doping concentrations. These luminescence characteristics of the doped samples may be attributed to the energy transfer between rare earth ions and CoO₆ octahedral groups in the columbite structure.