Rare-Earth-Free Phosphors Based on Vanadate Compounds

Abstract

Rare-earth-free phosphors based on vanadate compounds are described in this review paper. Rare-earths are used in the luminescent centers in various commercial inorganic phosphors and their constituents, as well as critical additives in other functional materials such as neodymium magnets and hydrogen storage alloys. Although exhaustion of the resources is not expected to occur in the near future, the steady supply has been affected by the absence of high-content ores. The high-cost for deduction from ores, refinement and purification is also a problem of rare-earths. A material design based on a rare-earth-free concept should therefore be considered a key technology for realization of a sustainably developing society. Although it is known that some vanadate compounds show photoluminescence under irradiation of ultra-violet (UV) light, the origin of the difference in the colors according to the compositions had not been clarified. We have recently reported several vanadate phosphors such as Sr₂VO₄Cl (deep-blue), Ca₂VO₄Cl (sky-blue), Ba₂V₂O₇ (green) and Zn₃(VO₄)₂ (yellow) and found an inverse correlation between the luminescent energies and the V-O distances in the VO₄ tetrahedra. Reddish luminescence was attained by reducing the electrostatic interaction between V⁵⁺ and X^n– (X: anion) with vanadium oxyfluorides, which is not obtained with oxide vanadate compounds.