Investigation of the CaO–La2O3–SiO2–P2O5 quaternary diagram. Synthesis, existence domain, and characterization of apatitic phosphosilicates

The CaO–La2O3–SiO2–P2O5 phase diagram was investigated in order to determine a domain inside which all points correspond to pure apatitic oxyphosphosilicates with the general formula CaxLay(SiO4)6−u(PO4)uOt. The prepared compounds were chemically analyzed and then characterized by X-ray diffraction method, infrared absorption, and Raman diffusion spectroscopies. The bands present in the IR and Raman spectra were identified and assigned to the corresponding vibration modes of SiO4 and PO4 anions. The Eu3+ luminescence study of some doped samples was carried out and their color points were determined. The present data show that a continuous solid solution is obtained inside the apatitic defined domain. Among the Eu3+-doped samples, the Ca2La8(SiO4)6O2:Eu(2%) can be used as a red phosphor.