We studied the effect of Mn concentration on the optical, morphological and magnetic properties of Zn_1−xMn_xTe NCs grown in a glass matrix produced by the fusion method. The physical properties of these materials were determined by optical absorption (OA), transmission electron microscopy (TEM), atomic/magnetic force microscopy (AFM/MFM) and photoluminescence (PL). An analysis of the OA spectra, based on the crystal field theory (CFT), showed strong evidence that Mn²⁺ ions were substitutionally incorporated into the Zn_1−xMn_xTe NCs until reaching the solubility limit (concentration, x = 0.100). Above this nominal concentration, TEM showed the onset of Mn-related phases, such as MnO and α-MnO₂, in the PZABP glass system. AFM images showed that NC density on the surface of the glass matrix decreased as x-content increased. It is probable that MnO and MnO₂ NCs would outnumber Zn_1−xMn_xTe NCs at higher concentrations – a conclusion that was corroborated by the OA spectra and TEM images. MFM images revealed that samples with Mn²⁺ ions responded to magnetization from an MFM probe. This implied that Mn²⁺ ions were incorporated within the Zn_1−xMn_xTe NCs and gave rise to the diluted magnetic semiconductor (DMS) structure. The PL spectra not only confirmed the evidence obtained by OA, CFT, TEM and AFM/MFM, but also showed that Mn²⁺ concentration could be used to tune ⁴T₁(⁴G) → ⁶A₁(⁶S) emission energy.