Current methods to prepare colloidal PbSe semiconductor nanocrystals involve acutely toxic trioctylphosphine as ligand and lead sources such as acetates and oxides. Furthermore, the resulting products have poorly controlled sizes and morphologies. Hao-Li Zhang and collaborators, Lanzhou University, China, have developed a preparation method that uses only oleylamine as both solvent and ligand and enables preparation of nanocrystals with controlled sizes and shapes.
When hot solutions of PbCl2 and Se in oleylamine are mixed, nanocrystals are quickly formed, as indicated by the black color of the mixture. Different reaction times and temperatures yield nanocrystals with different sizes. Short reactions at high temperature give small particles, e.g., 0.5 min at 220 °C for 7.5 nm particles, while larger particles can be prepared at lower temperature with longer reaction times, e.g., 190 °C for 120 min for 12.5 nm particles. The obtained nanocrystals show strong optical limiting effects, which makes them potential candidates for the development of nonlinear optical devices.
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