We analyze the mechanism of seeded growth reactions used to synthesize colloidal core/shell nanocrystals. Looking at the formation of CdSe/CdS and CdSe/ZnSe using both zinc blende and wurtzite CdSe seeds with a different surface termination, we show that the formation rate of the shell material does not depend on the presence of the seed nanocrystals. This suggests that shells grow by inclusion of CdS or ZnSe initially formed in the reaction mixture, possibly under the form of reactive monomers, and not by successive adsorption and reaction of metal and chalcogen precursors. This insight makes balancing homogeneous nucleation and heterogeneous growth of the shell material key to suppressing spurious secondary nucleation. Through a combination of experimental work and reaction simulations, we argue that this can be effectively achieved by raising the monomer solubility through the concentration of carboxylic acid used in the seeded growth reaction.

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We evaluated the effect of high-temperature treatment of Cd 0.9 Zn 0.1 Te:In single crystals using Hall-effect measurements, medium-and high-temperature annealing under various deviations from stoichiometry, and infra-red (IR) transmission microscopy Annealing at ~730 K sharply increased the electrical conductivity (by ~1-2 orders-of-magnitude). Plots of the temperature-and cadmium-pressure dependences of the electrical conductivity, carrier concentration, and mobility were obtained. Treating previously annealed Cd-samples under a Te overpressure at 1070 K allowed us to restore their resistance to its initial high values. The main difference in comparing this material with CdTe was its lowered electron density. We explained our results within the framework of Kröger's theory of quasi-chemical reactions between point defects in solids.

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Solid-state light-emitting diodes (LEDs) emit nearly monochromatic light, yet seamless tuning of emission color throughout the visible region remains elusive. Color-converting powder phosphors are therefore used for making LEDs with a bespoke emission spectrum, yet broad emission lines and low absorption coefficients compromise the formation of small-footprint monochromatic LEDs. Color conversion by quantum dots (QDs) can address these issues, but high-performance monochromatic LEDs made using QDs free of restricted, hazardous elements remain to be demonstrated. Here, we show green, amber, and red LEDs formed using InP-based QDs as on-chip color convertor for blue LEDs. Implementing QDs with near-unity photoluminescence efficiency yields a color conversion efficiency over 50% with little intensity roll-off and nearly complete blue light rejection. Moreover, as the conversion efficiency is mostly limited by package losses, we conclude that on-chip color conversion using InP-based QDs can provide spectrum-on-demand LEDs, including monochromatic LEDs that bridge the green gap.

We analyze the stability of the photoluminescence efficiency of flash core/shell quantum dots (QDs). We show that shell design is crucial to suppress thermal quenching and long-term photodegradation, where a radial composition change from CdS to ZnS results in QDs that surpass the stability requirements of display applications.

Using differential thermal analysis, we investigated the parameters of the processes of melting and crystallization of the CdTe-Al system near the CdTe side (CdTe + 2 mol. % Al, CdTe + 4 mol. % Al, and CdTe + 6 mol. % Al). By varying the melts' intermediate isothermal holding temperature for 10, 30, and 60 minutes whilst heating them up to 1423 K, we determined the conditions needed for the melts' full homogenization. We demonstrated that increasing the Al content changes the mechanism of the melting of the CdTe phase.