The study elucidates the step-by-step formation process of CsPbBr₃ perovskite nanocrystals within a borogermanate glass matrix. To regulate crystal growth stages, different precursor concentrations were used: 0.7 – 4.7 mol.% Br-, 0.2 – 5 mol.% PbO. Spectroscopic and structural analyses reveal three distinct stages: (1) At low concentrations, bromine-containing clusters form, exhibiting broadband blue luminescence centered at 430 nm, with anisotropy up to 0.15 and an average lifetime of ∼200 ns. (2) As PbO and Br– concentrations increase above 0.6 and 2.1 mol.%, respectively, CsPbBr₃ nanocrystals nucleate, showing characteristic emission between 498 and 522 nm. (3) An additional emission band at 470 nm emerges at intermediate precursor concentrations (0.6 – 2.6 PbO and 2.1 – 3.7 mol.% Br–). The highest luminescence quantum yield of perovskite glass-ceramics is 53 %. Additionally, X-ray diffraction analysis indicates a transition from cubic to orthorhombic perovskite structure with increasing precursor concentration, the orthorhombic phase becoming dominant above 2.6 mol.% PbO and 3.7 mol.% Br–. These results provide quantitative insights into cluster formation and perovskite crystallization within a glass-ceramic system, offering new avenues for tailoring optical properties.