A Photoetching-After-Growth Approach for the Synthesis of Nanocrystal Heterostructures Exhibiting Tunable Dual-Band Emission

Abstract

Introduced herein is a new strategy for synthesizing sophisticated colloidal semiconductor nanostructures with targeted optical properties by combining a conventional colloidal growth (bottom-up) process and a postgrowth photoetching (top-down) process. To demonstrate the utility of such photoetching-after-growth approach, a complex quantum dot (QD)-quantum rod (QR) dual quantum-confined domain nanocrystal heterostructure (NCH) is engineered which exhibits bright dual-band emission precisely tunable in a broad visible region. (CdSe/CdS)/ZnS/CdSe QD/barrier/multi-QR NCHs consisting of a single CdSe/CdS QD core and multiple CdSe QR branches with a wide-bandgap ZnS barrier between them are prepared through a multistep colloidal growth. The as-synthesized NCHs show a single emission band from QR; however, after photoetching, NCHs begin to display bright dual emission bands, a high-energy emission band from QR in addition to the low-energy emission band from QD. While the QD emission at 586 nm is determined by colloidal growth conditions, that of QR emission is precisely tunable in the 500-585 nm range by quantum-size-selective photoetching using a wavelength-tunable laser. Notably, the QR emission bandwidth decreases to approximate to 20 nm, which is close to that of a single CdSe nanorod, emphasizing a significant quantum-size-focusing effect of the photoetching process.