The aqueous synthesis and post-preparative treatment of thiol-stabilized ZnSe colloidal nanocrystals (2-3 nm in size) have been studied. The post-preparative irradiation of the nanoparticles improves their luminescence properties leading to strong (up to 25-30% photoluminescence quantum yield) band gap UV-blue emission. The irradiation results in an incorporation of sulfur into the particles and in the formation of ZnSe(S) alloyed nanocrystals. The ZnSe(S) nanocrystals obtained were used for the fabrication of UV-blue-emitting layer-by-layer assembled films with a PL maximum at ca. 390 nm.