Influence of anionic substitutions on the luminescent properties of Ca9.75Eu0.5(VO4)7

A series of substituted vanadates of Ca9.75±δEu0.5(XO4)0.1(VO4)6.9 (X ​= ​W6+, Nb5+, Ge4+, Cr6+, P5+) with Ca3(VO4)2-type structure have been synthesized via a standard solid-state method. Powder X-ray diffraction (PXRD), photoluminescence excitation (PLE) and emission (PL) spectra were used to characterize the solid solutions. The successful substitutions in the anionic part were confirmed using energy dispersive X-Ray (EDX), atomic emission spectrometry with inductively coupled plasma (ICP-OES) and the X-ray photoelectron spectroscopy (XPS) analyzes. All compounds crystallize in the noncentrosymmetric spаcе group R3c. The replacement of vanadium by other cations is accompanied by an increase in the second harmonic signal, with the exception of chromium. Red-to-orange (R/O) factors indicate a lower local symmetry of emitting Eu3+ ions environment in Ca9.75±δEu0.5(XO4)0.1(VO4)6.9 (X ​= ​W6+, Nb5+, Ge4+, Cr6+, P5+) in comparison to pure Ca9.75Eu0.5(VO4)7. Photoluminescence properties of Ca9.75±δEu0.5(XO4)0.1(VO4)6.9 systems were improved by NbO43− and GeO44− substitutions. The present study shows that Ge-incorporation in the β-Ca3(PO4)2 host increases the luminescence intensity in 2.5 times. The presented results indicate that the synthesized solid solutions can be considered as new single-phase phosphors.