Structural Phase Formation and Tunable Luminescence of Eu2+-Activated Apatite-Type (Ca,Sr,Ba)5(PO4)2(SiO4)

The samples on the base of the substitutions on Sr-cation in apatite Sr 5 (PO 4 ) 2 (SiO 4 ) were prepared by conventional solid-state reaction method: I) Sr 4.75-5x Ca 5 x (PO 4 ) 2 (SiO 4 ):Eu 0.25 2+ (0.01 ≤ x ≤ 0.95) and II) Sr 4.75-5 y Ba 5 y (PO 4 ) 2 (SiO 4 ):Eu 0.25 2+ (0.01 ≤ z ≤ 0.5). The crystal phase formations were investigated by the X-ray powder diffraction patterns. The tunable green-yellow color was detected due to the substitution of cation Sr 2+ in the host lattice by either Ca 2+ or Ba 2+ . The relationship between the structure and luminescence properties was reported. The site-occupation of Eu 2+ ions and energy transfer were discussed on the base of crystal structure. Partial substitution of Sr 2+ by either Ca 2+ or Ba 2+ all results in a blue-shifted Eu 2+ emission. The luminescence blue-shift is a common phenomenon in Ba 2+ -substition for Sr 2+ due to a decreased crystal field splitting for Eu 2+ on the bigger Ba 2+ cation site. However, in the Ca 2+ -substitution for Sr 2+ , the luminescence blue-shifted Eu 2+ emission is unusual. The detailed luminescence spectra of Eu 2+ ions in relation with the micro-structure were first reported in one of the end compound Ca 5 (PO 4 ) 2 (SiO 4 ). This is helpful to improve this series of materials for a potential application as a biomaterial or a phosphor for the lighting.