Multiphase Cd0.5Zn0.5S quantum dots (QDs) are prepared for the first time in a record minimum time of 30 min by mechanical alloying the stoichiometric mixture of elemental Cd, Zn and S powders at room temperature under Ar. Initially, the hexagonal phase is formed as major one and then gradually transforms to the cubic phase which is formed coherently on the hexagonal lattice with (0 0 2)(hexagonal)parallel to(1 1 1)(cubic) mechanism. In the course of milling up to 15 h, the molar ratio of cubic to hexagonal phase becomes similar to 0.7:0.3. Both high resolution transmission electron microscopy (HRTEM) and X-ray microstructure analyses reveal that these QDs are isotropic in nature, their size reduces to similar to 5 nm after 15 h of milling with a very narrow size distribution and they contain a significant amount of stacking and twin faults. These QDs show very distinct quantum confinement effect and their optical band gaps are higher than that of the bulk CdZnS. (C) 2012 Elsevier Ltd. All rights reserved.