In this study, a new series of phosphors, Casub.9−xZnxGdsub.0.9(POsub.4)sub.7:0.1Eusup.3+ (x = 0.00–1.00, step dx 0.05), was synthesized, consisting of centro- and non-centrosymmetric phases with β-Casub.3(POsub.4)sub.2-type structure. Crystal structures with space groups R3c (0.00 ≤ x < 0.35) and R3¯c (x > 0.8) were determined using X-ray powder diffraction and the method of optical second harmonic generation. In the region 0.35 ≤ x ≤ 0.75, phases R3c and R3¯c were present simultaneously. Refinement of the Casub.8ZnGd(POsub.4)sub.7 crystal structure with the Rietveld method showed that 71% of Gdsup.3+ ions are in M3 sites and 29% are in M1 sites. A luminescent spectroscopy study of Casub.9−xZnxGdsub.0.9(POsub.4)sub.7:0.1Eusup.3+ indicated the energy transfer from the crystalline host to the Gdsup.3+ and Eusup.3+ luminescent centers. The maximum Eusup.3+ luminescence intensity corresponds to the composition with x = 1.