Comparative study on blue-turquoise silicate apatite phosphors prepared via different synthesis routes

Different types of gel precursors were obtained via microwave-assisted precipitation, gel-combustion, sol–gel, and Pechini methods in order to prepare Ca₂Y_7.76Ce_0.12Tb_0.12(SiO₄)₆O₂ phosphors with apatite structure. The processes involved during the thermal treatment of precursors were revealed by TGA– FT-IR coupling. ICP-OES reveals that the incorporation degree of dopants (Ce³⁺, Tb³⁺) in silicate lattice are close to theoretical values while Ca²⁺ and Y³⁺ values shows differences depending on the synthesis route. The phosphors composition, morphology, structure, and optical characteristics are revealed by SEM, XRD, FTIR, and luminescent investigations. Pure hexagonal apatite with crystallite size of 76.5 nm was identified in sample prepared by gel-combustion, while cubic-Y₂O₃ and monoclinic-Y₂SiO₅, as secondary phases, were found in precipitated samples. The purity phase was enhanced by increasing the TEOS amount during precipitation. As a result of the Ce³⁺ incorporation into different symmetry sites, the excitation spectra are dominated either by 321 or 360 nm band. Turquoise emission of apatites is shifted toward blue region by increasing the excitation wavelength from 231 to 360 nm.