Eu3+ luminescence is studied in apatite-related phosphate BiCa4(PO4)3O. Compositions of the formula Bi1-xEuxCa4(PO4)3O [x=0.05, 0.1, 0.3, 0.5, 0.8 and 1.0] are synthesized and they are isostructural with parent BiCa4(PO4)3O. Room temperature photoluminescence shows the various transitions 5D 0→7FJ(=0,1,2) of Eu3+. The emission results of compositions with different Eu3+ content show the difference in site occupancy of Eu3+ in Bi1-xEu xCa4(PO4)3O. The intense 5D0-7F0 line at 574nm for higher Eu3+ content is attributed to the presence of strongly covalent Eu-O bond that is possible by substituting Bi3+ in the Ca(2) site. This shows the preferential occupancy of Bi3+ in Ca(2) site and this has been attributed to the 6s2 lone pair electrons of Bi3+. This is further confirmed by comparing the emission results with La 0.95Eu0.05Ca4(PO4)3O. © 2004 Elsevier Inc. All rights reserved.