Strong and Tunable Blue Luminescence from Cd1‑xZn x S Alloy Nanocrystallites Grown in Langmuir–Blodgett Multilayers

Cd1‑x Zn x S alloy nanocrystallites were grown in organic layered matrix by H2S exposure of precursor CdA-ZnA Langmuir–Blodgett multilayers at room temperature. The multilayers containing the alloy nanocrystallites were subsequently subjected to intercalation with Cd2+ ions followed by heat treatment up to 300 °C. With variation of the Zn content of precursor multilayers, the alloy nanocrystallites exhibit changes in lattice constants as well as a shift of excitonic absorption and emission between the extreme values for CdS and ZnS. The alloy nanocrystallites also exhibit treatment process dependent characteristic changes in optical absorption and luminescence, and the optical data have been used to propose suitable energy level diagrams. A strong enhancement of blue excitonic emission and suppression of emission due to bulk and surface defects are seen after postsulphidation treatments of the multilayers containing alloy nanocrystallites. These studies have shown that the organic moieties encapsulating the Cd1‑x Zn x S nanocrystallites tend to restrict their growth and aggregation, while the presence of cadmium species in the organic matrix in proximity with the nanocrystallites is responsible for the passivation of surface defects as well as the reduction of bulk defects.