Interdiffusion-enhanced cation exchange for HgSe and HgCdSe nanocrystals with infrared bandgaps

Abstract

Colloidal semiconductor nanocrystals based on CdSe have been precisely optimized for photonic applications in the visible spectrum, with modern products exhibiting structural uniformity, near 100% quantum yield and linewidths narrower than 100 meV. Here we report homogeneous nanocrystals with tunable bandgaps in the infrared spectrum based on HgSe and HgxCd1−xSe alloys deriving from CdSe precursors. We find that Ag+ catalyses cation interdiffusion to reduce the CdSe–HgSe alloying temperature from 250 °C to 80 °C. Together with ligands that modulate surface cation exchange rates, interdiffusion-enhanced Hg2+ exchange of diverse CdSe nanocrystals proceeds homogeneously and completely. The products retain the size, shape and uniformity of the parent nanocrystals but exhibit enhanced absorption. After passivation with heteroepitaxial CdZnS shells, photoluminescence wavelengths are tunable in the shortwave infrared by composition without changing size, with 80–91% quantum yield and linewidths near 100 meV. These materials may find applications in infrared photonic devices and infrared bioimaging. CdSe nanocrystals are used as synthetic templates for HgSe and alloyed HgxCd1−xSe nanocrystals with tunable, diverse structures. Cd2+-to-Hg2+ exchange occurs homogeneously and completely through interdiffusion enhancement with Ag+ catalysts and with surface cation exchange modulated by alkylthiol ligands.