The influence of second coordination-sphere interactions on the luminescent properties of β-Ca3(PO4)2-related compounds

CasCdEu(PO4)(7) polycrystalline material with a beta-Ca-3(PO4)(2)-type (beta-TCP) structure was obtained using a solid state technique. The structure was refined by Rietveld method using powder synchrotron X-ray diffraction data. The analysis of applying approaches confirmed that the CasCdEu(PO4)(7) structure is similar to R (3) over barc structures of Ca8MEu(PO4)(7) (M = Mg, Zn). The photoluminescence properties were studied under UV excitation and compared with previously investigated Ca8MEu(PO4)(7)(M = Mg, Zn, Ca). The substitution of Ca2+ by M2+ influences on the efficiency of energy transfer between the host and the luminescent ion. The influence of second coordination-sphere interactions on the luminescent properties of Ca8MEu(PO4)(7) was revealed. Based on the difference on the PL spectra of Eu3+ in Ca8MEu(PO4)(7) with R3c or R (3) over barc structures the site-selective method for determination of space group in beta-TCP-type compounds was proposed. It is thus shown that the Eu3+ was used as an optical probe to determine the site symmetry of studied hosts. (C) 2019 Elsevier B.V. All rights reserved.