Crystal Structure, Luminescence, and Thermodynamic Properties of Pb10 – xEux(GeO4)2 + x(VO4)4 – x (x = 0.1, 0.2, 0.3) Substituted Apatites

Pb10 – xEux(GeO4)2 + x(VO4)4 – x (x = 0.1, 0.2, 0.3) Eu-substituted lead germanatovanadates with the apatite structure have been prepared by solid-state reactions, via firing in air in the temperature range 773–1073 K, using oxides (PbO, Eu2O3, GeO2, and V2O5) as starting materials. Using X-ray diffraction, we have determined the hexagonal cell parameters (sp. gr. P63/m) of the synthesized phases and refined their crystal structure (the atomic position coordinates, isotropic thermal parameters, and principal bond lengths in their structure are presented). We have measured the luminescence spectra of the Pb10 – xEux(GeO4)2 + x(VO4)4 – x (x = 0.1, 0.2, 0.3) apatites and shown that europium concentration has little effect on the shape of the luminescence spectra. Using experimental heat capacity data obtained for polycrystalline samples by differential scanning calorimetry in the temperature range 350–1050 K, we calculated the main thermodynamic functions of the Eu-substituted lead germanatovanadates.