Highly efficient deep-blue emitting CsPbBr3 nanoplatelets synthesized via surface ligand-mediated strategy.

Two-dimensional (2D) CsPbBr3 nanoplatelets (NPLs) have attracted great attention as one of promising semiconductor nanomaterials due to their large exciton binding energy and narrow emission spectra. However, the labile ionic and weakly bound surfaces of deep-blue emitting CsPbBr3 NPLs with wide bandgap result in their colloidal instability, thus degrading their optical properties. It is challenging to obtain deep-blue emitting CsPbBr3 NPLs with excellent optical properties. In this study, high-quality blue-emitting CsPbBr3 NPLs with tunable thickness were prepared adopting the DBSA-mediated confinement effect based on the hot-injection method. Thanks to the coordination interaction of - SO3- of DBSA ligand and the Pb2+ on the surface of the CsPbBr3 NPLs, as well as the effective passivation of Br vacancy defects on the surface of NPLs by OAm-Br, the obtained pure-blue CsPbBr3 NPLs and deep-blue CsPbBr3 NPLs show high photoluminescence quantum yield (PLQY) of 92 % and 81.2 %, respectively. To the best of our knowledge, this is the highest PLQY recorded for deep-blue emitting CsPbBr3 NPLs with two monolayers [PbBr6]4- octahedra. Furthermore, the agglomeration of CsPbBr3 NPLs due to ligand loss induced by moisture, oxygen, and irradiation was also suppressed by the dual passivation effect of DBSA and OAm-Br. Our work provided a new approach to developing high-performance and stable deep-blue emitting CsPbBr3 perovskite nanoplatelets.

CdTe magic-size cluster synthesis via a cation exchange method and conversion mechanism.

The quasi-metallic nature of Te is not conducive to telluride formation and crystallization, which makes the synthesis of CdTe magic-size clusters (MSCs) in a single-ensemble form still challenging. CdTe MSCs are usually synthesized by direct synthesis, a method that must avoid the formation of quantum dots by selecting suitable active precursors and precisely controlling the reaction temperature. In addition, the organic Cd compounds and superhydrogenated precursors used are air-sensitive. Herein, CdTe MSC-448 in a single-ensemble form was synthesized for the first time via a cation exchange method using ZnTe MSC-389 as a template and Cd2+ as an exchange ion. In situ absorption spectroscopy characterization combined with the two-pathway model proposed by Yu's group reveals that the conversion of ZnTe MSC-389 into CdTe MSC-448 is assisted by their corresponding precursor compounds (PCs). After the addition of Cd precursors to ZnTe MSC-389 solution, ZnTe MSC-389 is transformed into ZnTe PC-389, which then undergoes a rapid cation exchange reaction with Cd2+ to yield CdTe PC-448, and CdTe PC-448 is finally converted into CdTe MSC-448. CdTe MSCs in single-ensemble form were obtained by cation exchange in air at room temperature, avoiding the formation of quantum dots (QDs) at high temperatures in the direct synthesis method conducted without the use of toxic and expensive active precursors, which provides a new route to the synthesis of CdTe MSCs.

Room-temperature formation of alloy ZnxCd13-xSe13 magic-size clusters via cation exchange in diamine solution.

Magic-size clusters (MSCs) are molecular materials with unique properties at the border between molecules and solids, providing important insights into the nanocrystal formation process. However, the synthesis of multicomponent alloy MSCs in a single-ensemble form remains challenging due to their tiny size and difficult doping control. Herein, for the first time, we successfully synthesized alloy ZnxCd13-xSe13 MSCs (x = 1-12) with a unique sharp absorption peak at 352 nm by cation exchange between Cd2+ ions and pre-synthesized (ZnSe)13 MSCs in a diamine solution at room temperature. The experimental results show that the use of diamines is crucial to the formation of stable ZnxCd13-xSe13 MSCs, which may be attributed to two amine groups that can coordinate to the surface of MSCs simultaneously. Limited by the robust interaction between diamine ligands and MSCs, the partial cation exchange results in the formation of alloy ZnxCd13-xSe13 MSCs. In contrast, complete cation exchange occurs in a monoamine solution, giving (CdSe)34 MSCs. Besides, a lower reaction temperature and a higher concentration of diamine favor the formation of ZnxCd13-xSe13 MSCs. Our study provides an important basis for further understanding of the transformation of MSCs and a new approach to the controllable synthesis of alloyed MSCs.