Luminescence and crystallographic sites for Eu3+ ions in Sr5(PO4)3F phosphor

This paper reports on the luminescence studies of Eu3+-doped strontium fluoroapatite. The goal of this paper is to establish and characterize the possible sites for Eu3+ substitution in Sr5(PO4)3F lattice. Eu3+-doped Sr5(PO4)3F phosphor was prepared by the solid state reaction method. The X-ray powder diffraction result of as-synthesized powder phosphor reveals the single phase Sr5(PO4)3F and it also indicates that the incorporation of Eu3+ ions does not affect the crystal structure. Photoluminescence (PL) studies of Eu3+-doped Sr5(PO4)3F phosphor are performed to study spectral properties of the sample. Site-selective excitation and emission spectra together with the decay curves are investigated by site-selective laser-excitation spectroscopy. The three crystallographic sites for Eu3+ ions are identified in the 7F0 → 5D0 excitation spectra by using a pulsed, tunable, and narrowband dye laser. The luminescence due to the 5D0 → 7FJ (J = 1, 2) transitions under excitation at each crystallographic site exhibits its own spectral features. Three crystallographic sites in Sr5(PO4)3F give rise to different crystal-field splits of the 7F1 and 7F2 multiplets. Heterovalent substitution by rare-earth ions (Eu3+) for Ca2+ positions in the hexagonal crystal lattice requires charge compensation. The charge-compensation mechanism, site symmetry, and the crystal-field strength on Eu3+ in Sr5(PO4)3F are discussed for better understanding of preferential substitution of Eu3+ in the Sr5(PO4)3F lattice.