Influence of 6s² lone pair electrons of Bi³⁺ on its preferential site occupancy in fluorapatite, NaCa<inf>3</inf>Bi(PO <inf>4</inf>)<inf>3</inf>F - An insight from Eu³⁺ luminescent probe

Eu3+ luminescence was used as a structural probe in understanding the preferential site occupancy of lone pair cation, Bi 3+, in fluorapatite by comparing the photoluminescence (PL) emission spectral features with that of in analogous La3+ based fluorapatite. The fluorapatites, NaCa3Bi0.95Eu0.05(PO 4)3F and NaCa3La0.95Eu 0.05(PO4)3F, were synthesized by conventional high temperature solid state reaction method and characterized by powder X-ray diffraction (XRD) and FT-IR spectroscopy. The Eu3+ PL results revealed a difference in the emission spectral features in NaCa 3Bi0.95Eu0.05(PO4)3F and NaCa3La0.95Eu0.05(PO4)3F. This difference in Eu3+ PL emission can be attributed to the difference in its site occupancy in the studied fluorapatites. © 2014 Elsevier Ltd.