We have studied the low temperature excitonic reflectance and luminescence spectra of CdS_1-xSe_x solid solutions with a near-surface excitonic potential well formed by excessive Se. The reflectance spectra were obtained at different angles of incidence for both s- and p-polarization components of light. New striking spectral features due to exciton confinement and quantization in the surface region were observed. For various samples, the generalized Morse surface potential was proved to be a good approximation in describing the experimental data. It is shown that the resonance excitonic luminescence is largely governed by the emission from excitations localized in the well.