The fluorescence of CdSxSe1-x mixed crystals with band-gap gradients as large as 1200 eV/cm has been investigated at 77°K. The graded samples were produced by heating CdSe or CdSxSe1-x platelets in a sulfur-selenium atmosphere. Some of the diffused crystals were post-treated in a cadmium atmosphere. Removal of surface material shifted the fluorescence spectra of the diffused crystals to longer wavelengths. The spectral position of fluorescence peaks was determined as a function of the thickness of the removed surface layer. Composition profiles were deduced from these data by correlating fluorescence wavelength with crystal composition. Error-function curves gave a good fit to experimentally determined profiles. Diffusion constants of 7.0 × 10-13 and 1.6 × 10-12 cm2/sec were determined for diffusion temperatures of 600 and 650°C, respectively.