ON the interconfigurational 4fn↔4fn−15d1 optical transitions of Ce3+ and Pr3+ in Ca9R3+ (PO4)7 [R3+=Al, Ga, Sc, Lu, Y, Gd, La]

Abstract A systematic study of the optical properties of Ce 3+ and Pr 3+ in Ca 9 R 3+ (PO 4 ) 7 [R 3+ =Al, Sc, Lu, Y, Gd, La] is presented. The materials crystallize in the Whitlockite structure of β-Ca 3 (PO 4 ) 2 . From the room temperature excitation spectra, the crystal-field splitting and centroid shift of the Ce 3+ 5d 1 configuration is estimated. The optical properties (crystal-field splitting, the centroid shift and Stokes shift of emission) of Ce 3+ is independent of the R 3+ cation in Ca 9 R 3+ (PO 4 ) 7 . It is concluded that in this family of materials and in the parent β-Ca 3 (PO 4 ) 2 lattice, the Ce 3+ and Pr 3+ preferentially occupy the eight coordinated 18(b) Ca(3) site of the R3c space group. Relative to other phosphates, the covalence of the Ce 3+ –O 2− bonding is high in this family of orthophosphate materials.