Large quantities of free standing quasi mono-disperse silicon nanocrystal/silicon oxide core-shell structured particles have been segregated by a cyclic process of sonication and centrifugation of mechanically milled and chemically treated colloidal suspension of silicon powders in ethanol medium. Narrowing of size distribution with the enhancement of centrifugation time has been evidenced from different structural characterisations as well as optical absorption and photoluminescence study. Gradual shifting of photoluminescence peak positions towards higher energy region in samples, prepared through longer centrifugation time, is also detectable with unaided eye when different samples are exposed to laser beam of wavelength similar to 405 nm. Controlled optoelectronic properties of the final sample achieved after four such cycles indicate a narrow core size distribution centering at 2.15 nm; can also be evidenced from the TEM micrograph.