Tuning Bismuth Activator Valence in Calcium Halophosphate Solid Solution by Controlling Activator Site

Effect of halide ions on valence state and luminescence property of Bi ions in calcium halophosphates was investigated. Bi-activated fluorapatite-chlorapatite solid solutions were synthesized by a solid state reaction. The content ratio between Bi 2+ and Bi 3+ ions in the crystals could be tuned rationally by the component ratio of F -/Cl -, and the absent emission of Bi 2+ ion occur when halide ions are all occupied by Cl -ions. The origin of this change is because the Ca 2 site of calcium halophosphate is split into Ca(2)a and Ca(2)b sites for F -and Cl -as the nearest neighbors, and the Ca(2)a is adopted to offer activator site that enables Bi 3+ to be self-reduced. The results in this study can provide a scientific reference for controlling the valence state of Bi ions in crystals.