Synthesis and Spectroscopy of Emissive, Surface-Modified, Copper-Doped Indium Phosphide Nanocrystals

Aminophosphine precursors were used to synthesize copper-doped indium phosphide nanocrystals (InP NCs) via direct doping in a slow-injection bottom-up method and postsynthetic cation exchange. By both methods, the amount of copper incorporated into the NCs could be tuned simply by varying the molar ratio during synthesis. Common postsynthetic surface modifications such as Lewis acid treatment and zinc chalcogenide shelling were performed on these samples, resulting in an enhancement of the copper-based emission from 10% to 40%. For samples with thick shells, the copper-based photoluminescence quantum yield reached over 60%, a record value for doped InP NCs. Time-resolved photoluminescence spectroscopy showed increasing carrier lifetimes after surface treatments concurrent with the disappearance of a 2 ns decay process previously attributed to surface trapping in native InP NCs, showing the broad applicability and consistent impacts of the surface treatments. In this way, we have successfully developed a route to obtain high-quality near-infrared emitters utilizing less toxic alternatives to the popular lead- and cadmium-containing materials.