Type-II\nCdSe/CdTe Core/Crown Semiconductor\nNanoplatelets

Abstract

We have synthesized\natomically flat CdSe/CdTe core/crown nanoplatelets\n(NPLs) with thicknesses of 3, 4, and 5 monolayers with fine control\nof the crown lateral dimensions. In these type-II NPLs, the charges\nseparate spatially, and the electron wave function is localized in\nthe CdSe core while the hole wave function is confined in the CdTe\ncrown. The exciton’s recombination occurs across the heterointerface,\nand as a result of their spatially indirect band gap, an important\nemission red shift up to the near-infrared region (730 nm) is observed\nwith long fluorescence lifetimes that range from 30 to 860 ns, depending\non the type of interface between the core and the crown. These type-II\nNPLs have a high quantum yield of 50% that can be further improved\nto 70% with a gradient interface. We have characterized these novel\nCdSe/CdTe core/crown NPLs using UV–vis, emission, and excitation\nspectroscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy,\nand high-resolution transmission electron microscopy.