In this work, we reported the morphology evolution (formation of voids & size reduction) of gradient-alloyed CdxZn1–xSeyS1–y@ZnS quantum dots under electron irradiation during transmission electron microscopy observation. By investigating the correlations between shell gradients and morphology evolution, the formation of voids can be explained by the continuous electron irradiation-induced atomic movement under interfacial strain. On the other hand, the size reduction can be attributed to the elastic scattering-enabled sputtering of surface atoms. The as-formed voids of CdxZn1–xSeyS1–y@ZnS quantum dots with CdS-rich cores are much larger than those of ZnSe-rich ones, and the sizes of voids decreased with the increasing of shell thickness. The comparison of the morphology evolution of CdxZn1–xSeyS1–y@ZnS core–shell quantum dots with different composition gradients demonstrated that the size and shape of as-formed voids illustrate the strain characteristics of shell gradient. This provides a guideline to understand the strain effects in gradient-alloyed core–shell quantum dots through transmission electron microscopy measurement. We believe the deep insights into gradient-alloyed CdxZn1–xSeyS1–y@ZnS core–shell quantum dots would push forward their optimization toward commercialized light-emitting technology.
Gradient-alloyed Cd x Zn 1− x Se y S 1− y @ZnS core shell quantum dots are the most popular materials used in light-emitting diodes for liquid crystal display backlights. High-temperature photoluminescence is an essential property in determining the chromaticity shifts of on-chip type devices. In this work, the photoluminescence quenching effect of Cd x Zn 1− x Se y S 1− y @ZnS quantum dots is investigated by measuring the steady and time-resolved PL spectra at elevated temperatures. The thermal quenching of Cd x Zn 1− x Se y S 1− y @ZnS quantum dots can be explained by a thermally activated physical process, including electron resonance tunneling into pre-existing surface trap states, injection over the barrier energy back to the core, and recombination with the confined holes. By combing the theoretical analysis and experimental results, the influence of core composition and shell thickness of Cd x Zn 1− x Se y S 1− y @ZnS QDs on the quenching effect is illustrated. It is found that the integrated photoluminescence intensity of ZnSe-rich quantum dots with 20 monolayers ZnS shell at 500 K can reserve 85.1%, relative to the value at 300 K. Quantum dots with enhanced photoluminescence emission at high temperature enable the fabrication of light-emitting diodes with reduced chromaticity shifts.
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