The paper presents an experimental substantiation of the theory (based on the optical vibration anharmonism) of nonlinear Raman scattering (RS) in defective II-III₂-VI₄ compounds. In the transparency region of those compounds the an- harmonicity assures processes of direct photon-phonon interaction resulting in the independence of RS characteristics upon the free carrier concentration. When the laser quantum energy approaches the band gap E_g an effective thermaliza- tion of the absorbed radiation takes place which in one’s turn gives rise to the anharmonic generation of two or more phonons by a laser photon. These phenomena are shown to result in a non-linear dependence of the RS intensity upon the laser beam power.