Synthesis and VUV–UV spectroscopic properties of rare earth borosilicate oxyapatite: RE5Si2BO13:Ln3+ (RE=La, Gd, Y; Ln=Eu, Tb)

Three rare earth borosilicate oxyapatites, RE5Si2BO13 (RE=La, Gd, Y), were synthesized via wet chemical method, of which RE5Si2BO13 (RE=Gd, Y) were first reported in this work. In the three oxyapatites, [BO4] and [SiO4] share the [TO4] tetrahedral oxyanion site, and RE3+ ions occupy all metal sites. The differential scanning calorimetry–thermo gravimetry measurements and high temperature powder X-ray diffraction pattern revealed a vitrification process within 300–1200 °C, which was due to the glass-forming nature of borosilicates. From the VUV excitation spectra of Eu3+ and Tb3+ in RE5Si2BO13, the optical band gaps were found to be 6.31, 6.54 and 6.72 eV for RE5Si2BO13 (RE=La, Gd, Y), respectively. The emission and excitation bands of Eu3+ and Tb3+ are discussed relating with their coordination environments. Among the three hosts, Y5Si2BO13 would be the best for Eu3+ and Tb3+-doped phosphors.