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Dimension-engineered synthesis of atomically thin II–VI nanoplatelets (NPLs) remains an open challenge. While CdSe NPLs have been made with confinement ranging from 2 to 11 monolayers (ML), CdTe NPLs have been significantly more challenging to synthesize and separate. Here we provide detailed mechanistic insight into the layer-by-layer growth kinetics of the CdTe NPLs. Combining ensemble and single-particle spectroscopic and microscopic tools, our work suggests that beyond 2 ML CdTe NPLs, higher ML structures initially appear as heteroconfined materials with colocalized multilayer structures. In particular, we observe strongly colocalized 3 and 4 ML emissions, accompanied by a broad trap emission. Accompanying transient absorption, single-particle optical, and atomic force microscopy analyses suggest islands of different MLs on the same NPL. To explain the nonstandard nucleation and growth of these heteroconfined structures, we simulated the growth conditions of NPLs and quantified how the monomer binding energy modifies the kinetics and permits single NPLs with multi-ML structures. Our findings suggest that the lower bond energy associated with CdTe relative to CdSe limits higher ML syntheses and explains the observed differences between CdTe and CdSe growth. 

The total photon economy of a chromophore molecular species represents a study of how absorbed photons partition among various electronic states and ultimately dissipate their excited energy into the environment. 

We demonstrate a low-temperature synthesis of ultrasmall (<2 nm) HgTe quantum dots (QDs) with superlative optical properties in the near and shortwave infrared. The tunable cold-injection synthesis produces HgTe QDs ranging from 1.7 to 2.3 nm in diameter, with photoluminescence maxima ranging from 900 to 1180 nm and a full-width at half-maximum of ∼100 nm (∼130 meV). The synthesized quantum dots display high photoluminescence quantum yields (PLQY) ranging from 80 to 95% based on both relative and absolute methods. Furthermore, samples retain their high PLQY (∼60%) in the solid state, allowing for first-of-their-kind photoluminescence imaging and blinking studies of HgTe QDs. The facile synthesis allows for the isolation of small, photostable HgTe quantum dots, which can provide valuable insight into the extremes of quantum confinement. 

Large area absorbers with localized defect emission are of interest for energy concentration via the antenna effect. Transfer between 2D and 0D quantum-confined structures is advantageous as it affords maximal lateral area antennas with continuously tunable emission. We report the quantum efficiency of energy transfer in in situ grown HgTe nanoplatelet (NPL)/quantum dot (QD) heterostructures to be near unity (>85%), while energy transfer in separately synthesized and well separated solutions of HgTe NPLs to QDs only reaches 47 ± 11% at considerably higher QD concentrations. Using Kinetic Monte Carlo simulations, we estimate an exciton diffusion constant of 1–10 cm2/s in HgTe NPLs, the same magnitude as that of 2D semiconductors. We also simulate in-solution energy transfer between NPLs and QDs, recovering an R–4 dependence consistent with 2D-0D near-field energy transfer even in randomly distributed NPL/QD mixtures. This highlights the advantage of NPLs 2D morphology and the efficiency of NPL/QD heterostructures and mixtures for energy harvesting. 

Quantitative fluorescence quenching is a common analytical approach to studying the mechanism of chemical reactions. The Stern–Volmer (S–V) equation is the most common expression used to analyze the quenching behavior and can be used to extract kinetics in complex environments. However, the approximations underlying the S–V equation are incompatible with Förster Resonance Energy Transfer (FRET) acting as the primary quenching mechanism. The nonlinear distance dependence of FRET leads to significant departures from “standard” S–V quenching curves, both by modulating the interaction range of donor species and by increasing the effect of component diffusion. We demonstrate this inadequacy by probing the fluorescence quenching of long-lifetime lead sulfide quantum dots mixed with plasmonic covellite copper sulfide nanodisks (NDs), which serve as perfect fluorescent quenchers. By applying kinetic Monte Carlo methods, which consider particle distributions and diffusion, we are able to quantitatively reproduce experimental data, which show significant quenching at very small concentrations of NDs. The distribution of interparticle distances and diffusion are concluded to play important roles in fluorescence quenching, particularly in the shortwave infrared, where photoluminescent lifetimes are often long relative to diffusion time scales.