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The silicate oxyapatite materials are known for their structural flexibilities, high melting temperatures and good chemical stabilities. Therefore, various applications for this group of materials have been explored. In the present work, synthesis methods, crystal structures and the optical properties including potential optical applications of silicate oxyapatite Sr2Y8(SiO4)6O2 based materials are studied. Pure Sr2Y8(SiO4)6O2 powders are synthesized by both solid state reaction and sol-gel method. The crystal structure characterizations of Sr2Y8(SiO4)6O2 show that its symmetry belongs to P63/m. The general formula of silicate oxyapatite materials is A4A6(SiO4)6O2 and in the current case, half of A sites are occupied by Sr while the other half of A sites and all the A sites are filled by Y. The crystal structures and the photoluminescent properties of Eu doped Sr2Y8(SiO4)6O2 with different Eu concentrations are investigated. The XRD and Rietveld refinement revealed that most Eu cations entered A sites in low europium concentration (x = 0~0.5). At increased Eu concentration (x > 0.5), Eu cations also occupy A sites but the preference to the A sites still maintained. Photoluminescent properties vary with Eu concentrations according to photoluminescent spectra. Sr2Y6Eu2(SiO4)6O2 from sol-gel method appears to be the one with the strongest emission in nearly pure red color, whose intensity is comparable to commercial fluorescent lamp phosphor Eu:Y2O3, demonstrating potential as a red phosphor for the white LEDs. The translucent silicate oxyapatite Sr2Y8(SiO4)6O2 ceramic with a low porosity of about 0.7% is successfully fabricated by employing the spark plasma sintering. The total forward transmittance is about 52% but the in-line transmittance is much lower. Calculation reveals that influence of residual pores on the in-line transmittance is more significant than that of the birefringence effect. Though previous studies of translucent ceramics fabricated by spark plasma sintering with luminescent properties are limited, the translucent Ce doped Sr2Y8(SiO4)6O2 ceramics with different Ce concentration are fabricated by spark plasma sintering in this work and their photoluminescent properties are studied. The energy transfer process between Ce cations at A and A is revealed.

Synthesis, crystal structures and optical properties of rare earth silicate oxyapatite