Influence of 6s2 lone pair electrons of Bi3+ on its preferential site occupancy in fluorapatite, NaCa3Bi(PO4)3F – An insight from Eu3+ luminescent probe

Eu3+ luminescence was used as a structural probe in understanding the preferential site occupancy of lone pair cation, Bi3+, in fluorapatite by comparing the photoluminescence (PL) emission spectral features with that of in analogous La3+ based fluorapatite. The fluorapatites, NaCa3Bi0.95Eu0.05(PO4)3F and NaCa3La0.95Eu0.05(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 NaCa3Bi0.95Eu0.05(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.