Temporal evolutions of the photoluminescence quantum yields of colloidal InP, InAs and their core/shell nanocrystals

Colloidal InP, InAs and their core/shell nanocrystals are synthesized using in situ generated PH3 and AsH3, respectively. The optical stability of these nanocrystals is studied by monitoring the absorption and photoluminescence spectra. The quantum yield or photoluminescence intensity of InP nanocrystals synthesized in the presence of zinc stearate increases monotonously from 3% to 16%, while the photoluminescence peak position remains invariable during storage for 30 days in hexane and in the dark. On the contrary, InAs nanocrystals synthesized in the presence or absence of zinc stearate lose their photoluminescence gradually and show a reduction in their size during storage. For the core/shell nanocrystals, InP/ZnS nanocrystals exhibit fine optical stability in the first few days and a small decrease in the photoluminescence quantum yield from 15 to 30 days. InAs/ZnSe nanocrystals with different shell thicknesses show a monotonous increase in the quantum yield and blue-shift in the photoluminescence peak in the course of 30 days. Moreover, despite two shells, InAs/ZnSe/ZnS nanocrystals are still sensitive to surface states. The experiments show slight surface oxidation eliminates dangling bonds and leads to enhancement of photoluminescence. Furthermore, strong oxidation results in the formation of an oxide layer on the nanocrystal surface, giving rise to a reduction in photoluminescence.