The solid solution Ca9Zn1–xMnxNa(PO4)7(0 ≤x≤ 1.0) was obtained by solid-phase reactions under the control of a reducing atmosphere. It was demonstrated that Mn2+-doped phosphors can be obtained using activated carbon in a closed chamber, which is a simple and robust method. The crystal structure of Ca9Zn1–xMnxNa(PO4)7corresponds to the non-centrosymmetric β-Ca3(PO4)2type (space groupR3c), as confirmed by powder X-ray diffraction (PXRD) and optical second-harmonic generation methods. The luminescence spectra in visible area consist of a broad red emission peak centered at 650 nm under 406 nm of excitation. This band is attributed to the4T1→6A1electron transition of Mn2+ions in the β-Ca3(PO4)2-type host. The absence of transitions corresponding to Mn4+ions confirms the success of the reduction synthesis. The intensity of the Mn2+emission band in Ca9Zn1–xMnxNa(PO4)7rising linearly with increasing ofxat 0.05 ≤x≤ 0.5. However, a negative deviation of the luminescence intensity was observed atx= 0.7. This trend is associated with the beginning of a concentration quenching. At higherxvalues, the intensity of luminescence continues to increase but at a slower rate. PXRD analysis of the samples withx= 0.2 andx= 0.5 showed that Mn2+and Zn2+ions replace calcium in theM5 (octahedral) sites in the β-Ca3(PO4)2crystal structure. According to Rietveld refinement, Mn2+and Zn2+ions jointly occupy theM5 site, which remains the only one for all manganese atoms within the range of 0.05 ≤x≤ 0.5. The deviation of the mean interatomic distance (∆l) was calculated and the strongest bond length asymmetry, ∆l= 0.393 Å, corresponds tox= 1.0. The large average interatomic distances between Mn2+ions in the neighboringM5 sites are responsible for the lack of concentration quenching of luminescence belowx= 0.5.