In this paper, we study the optical properties of aluminum- and silicon-nitride films and Al–Si–N coatings with variable atomic composition deposited by reactive magnetron sputtering on glass, silicon, and steel substrates. The absorption and luminescence characteristics are determined by the composition of the coatings and microstructure and depend on the physical properties of the substrate. The absorption and luminescence centers are associated with intrinsic defects in the nitrides and their simplest complexes. The relationships between the accumulation of growth defects, their interaction, the type of distribution of localized states, the band gap, and the stability of the optical properties are established. At an increase in the silicon content in the coatings, the degree of static induced disorder increases, and the contribution of the continuous distribution of the defect levels and interband absorption increases. Silicon-containing defects stabilize the optical properties of the coatings.