Core/Barrier/Multi-Branch Nanocrystal Heterostructure with Tunable Dual-Band Emission

Abstract

Colloidal semiconductor nanocrystals displaying dual-band emission are of great interest due to complex multi-carrier interaction and relaxation dynamics in nanostructures having multiple emissive states, which have potential applications in white light generation, multimodal imaging, radiometric sensing, and quantum light source. Numerous dual-emitting nanostructures have been introduced and all have demonstrated some degree of spectral tuning by controlling structure and composition during colloidal growth. Here, we report a new dual-emitting nanostructure whose emission spectrum can be widely and continuously tailored by using a post-growth photoetching process. We synthesized a core/barrier/multi-branch nanocrystal heterostructure (NCH), that is a dual quantum system composed of a single quantum dot core and multiple quantum rod branches. A wide-bandgap barrier that electronically separates the two quantum systems allowed both core and branches to be brightly emissive (total QY up to ~40%) under ambient excitation fluence (1–10 nW/cm2). More importantly, the dual-band spectrum were continuously tuned by controlling the branch emission by applying photoetching. The quantum size-selective photoetching enabled precise tuning of the branch emission in a broad visible range (500–585 nm) while significantly narrowing the bandwidth (FWHM ~20 nm). Time-resolved fluorescence decay and photoluminescence excitation spectroscopy studies respectively confirmed that the dual emissions were from the two distinct quantum systems (dot and rod) and the presence of significant non-radiative energy transfer from the wider-bandgap branches to the narrower-bandgap core were present. Our work suggests a novel and versatile strategy of designing dual-emitting nanocrystals with wide and precise spectral tuning by controlled photoetching.