A study was carried out on the dependence of the optical properties such as the maxima in the absorption and luminescence spectra, Stokes shift, and quantum yield on the composition of the three-component Cd-L-Cys-S reaction system under synthesis conditions at 298 ± 2 K and pH 7. Equations describing the dependence of the position of the maximum in the luminescence and absorption spectra of solutions on their composition were obtained by mathematical planning using the Scheffe simplex-lattice design and treatment of the data. The region of compositions for unstable colloidal solutions was determined.