Shape-Dependent Multiexciton Emission and Whispering Gallery Modes in Supraparticles of CdSe/Multishell Quantum Dots

Abstract

Semiconductors are indispensable as the active light-emitting element in many optoelectronic devices. However, even the purest bulk semiconductors suffer from considerable nonradiative recombination leading to low photoluminescence efficiencies. Zero-dimensional quantum dots show a much better carrier-to-photon conversion caused by confinement of the excitons but suffer from nonradiative recombination when assembled into a solid, due to exciton energy transfer. Here, we report on the shape-dependent optical properties of self-assembled supraparticles composed of CdSe/multishell nanocrystals. All supraparticles show stable and bright photoluminescence in ambient up to high excitation intensities. When the supraparticles are deposited on a silicon surface their spherical shape is deformed due to drying. In addition to single-exciton emission, we observe bright emission from multiexciton states at high excitation powers. In contrast, supraparticles that retain their perfectly spherical shape show a spectrum with sharp Mie whispering gallery modes, while multiexciton emission is absent.

Nanoparticle Clusters: Assembly and Control Over Internal Order, Current Capabilities, and Future Potential

“…Vanmaekelbergh et al used micelle collapse to prepare NPCs from CdSe (core) CdS/CdZnS/ZnS (multishell) quantum dots (see Figure 8). [108] After evaporation of the apolar phase, monodisperse and highly ordered compact NPCs could be prepared in the size range from ca. 100 nm up to several micrometers.…”

“…After allowing the NPCs to spontaneously accumulate at the tumor site due to the enhanced permeability and retention (EPR) of the tumor tissues, they provided a clear contrast when observed using whole-animal CT and PL imaging (Figure 9a Reproduced with permission. [108] Copyright 2015, American Chemical Society.…”

Excited-State Dynamics in Colloidal Semiconductor Nanocrystals

“…Colloidal NCs can also self-assemble into three-dimensionally ordered colloidal superparticles [131]. The geometry and properties of these superstructures can be tailored by the size, shape, composition and surface chemistry of the NC or hetero-NC building blocks [129–138]. In particular, surface ligands have been shown to have a dramatic impact on the directionality of the self-organization process [135, 139–143], leading in some cases to atomically aligned NC superlattices [135, 139, 143].…”

Excited-State Dynamics in Colloidal Semiconductor Nanocrystals

“…Colloidal NCs can also selfassemble into three-dimensionally ordered colloidal superparticles [131]. The geometry and properties of these superstructures can be tailored by the size, shape, composition and surface chemistry of the NC or hetero-NC building blocks [129][130][131][132][133][134][135][136][137][138]. In particular, surface ligands have been shown to have a dramatic impact on the directionality of the self-organization process [135,[139][140][141][142][143], leading in some cases to atomically aligned NC superlattices [135,139,143].…”