Controlled Dopant Migration in CdS/ZnS Core/Shell Quantum Dots

The physical properties of a doped quantum dot (QD) are strongly influenced by the dopant site inside the host lattice, which determines the host–dopant coupling from the overlap between the dopant and exciton wave functions of the host lattice. Although several synthetic methodologies have been developed for introducing dopants inside the size-confined semiconductor nanocrystals, the controlled dopant-host lattice coupling by dopant migration is still unexplored. In this work, the effect of lattice mismatch of CdS/ZnS core/shell QDs on Mn­(II) dopant behavior was studied. It was found that the dopant migration toward the alloyed interface of core/shell QDs is a thermodynamically driven process to minimize the lattice strain within the nanocrystals. The dopant migration rate could be represented by the Arrhenius equation and therefore can be controlled by the temperature and lattice mismatch. Furthermore, the energy transfer between host CdS QDs and dopants can be finely turned in a wide range by dopant migration toward the alloyed interface during ZnS shell passivation, which provides an efficient method to control both the number of the emission band and the ratio of the emission from the host lattice and dopant ions

General Strategy for the Growth of CsPbX₃ (X = Cl, Br, I) Perovskite Nanosheets from the Assembly of Nanorods

Shape control is critical and offers an efficient way to tune the properties of nanocrystals (NCs). Here we present the growth of two-dimensional (2-D) all-inorganic CsPbX₃ (X = Cl, Br, I) perovskite NCs through the assembly of corresponding 1-D nanorods (NRs) under solvothermal conditions. Both 2-D CsPbX₃ perovskite nanoplatelets (NPLs) and nanosheets (NSs) with a wide lateral size range from ∼100 nm to ∼1 μm and thickness of a few unit cells can be obtained by the control of the solvothermal reaction time. The present work provides a general strategy for rational fabrication of 2-D CsPbX₃ (X = Cl, Br, I) perovskite NCs without the assistance of anion exchange. The obtained fluorescent 2-D all-inorganic perovskite NCs have great potential in practical photovoltaic applications

Interface Engineering of Mn-Doped ZnSe-Based Core/Shell Nanowires for Tunable Host–Dopant Coupling

Transition metal ion doped one-dimensional (1-D) nanocrystals (NCs) have advantages of larger absorption cross sections and polarized absorption and emissions in comparison to 0-D NCs. However, direct synthesis of doped 1-D nanorods (NRs) or nanowires (NWs) has proven challenging. In this study, we report the synthesis of 1-D Mn-doped ZnSe NWs using a colloidal hot-injection method and shell passivation for core/shell NWs with tunable optical properties. Experimental results show optical properties of the NWs are controlled by the composition and thickness of the shell lattice. It was found that both the host–Mn energy transfer and Mn–Mn coupling are strongly dependent on the type of alloy at the interface of doped core/shell NWs. For Mn-doped type I ZnSe/ZnS core/shell NWs, the ZnS shell passivation can enhance florescence quantum yield with little effect on the location of the incorporated Mn dopant due to the identical cationic Zn²⁺ site available for Mn dopants throughout the core/shell NWs. However, for Mn-doped quasi type II ZnSe/CdS NWs and ZnSe/CdS/ZnS core/shell NWs, the cation alloying (Zn_1–<i>x</i>Cd_<i>x</i>S­(e)) can lead to metal dopant migration from the core to the alloyed interface and tunable host–dopant energy transfer efficiencies and Mn–Mn coupling. As a result, a tunable dual-band emission can be achieved for the doped NWs with the cation-alloyed interface. The interfacial alloying mediated energy transfer and Mn–Mn coupling provides a method to control the optical properties of the doped 1-D core/shell NWs