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Very recently, two-dimensional (2D) perovskite nanosheets (PNSs), taking the advantages of perovskite as well as the 2D structure properties, have received an enormous level of interest throughout the scientific community. In spite of this incredible success in perovskite nanocrystals (NCs), self-assembly of many nanostructures in metal halide perovskites has not yet been realized, and producing highly efficient red-emitting PNSs remains challenging. In this Letter, we show that by using CsPbBrI2 perovskite nanoparticles (NPs) as a building block, PNSs can emerge spontaneously under high ambient pressure via template-free self-assembly without additional complicated operation. It is found that the formation of PNSs is ascribed to the high pressure that provides the driving force for the alignment of NPs in solution. Because of the disappearance of the grain boundaries between the adjacent NPs and increased crystallinity, these PNSs self-assembled from NPs exhibit enhanced properties compared to the initial NPs, including higher PL intensity and remarkable chemical stability toward light and water.

Lead halide perovskite quantum dots (PQDs) are reported as a promising branch of perovskites, which have recently emerged as a field in luminescent materials research. However, before the practical applications of PQDs can be realized, the problem of poor stability has not yet been solved. Herein, we propose a trioctylphosphine (TOP)-assisted pre-protection low-temperature solvothermal synthesis of highly stable CsPbBr 3 /TiO 2 nanocomposites. Due to the protection of branched ligands and the lower temperature of shell formation, these TOP-modified CsPbBr 3 PQDs are successfully incorporated into a TiO 2 monolith without a loss of fluorescence intensity. Because the excellent nature of both parent materials is preserved in CsPbBr 3 /TiO 2 nanocomposites, it is found that the as-prepared CsPbBr 3 /TiO 2 nanocomposites not only display excellent photocatalytic activity but also yield improved PL stability, enabling us to build highly stable white light-emitting diodes and to photodegrade rhodamine B.

Among the lead halide perovskites, photoluminescence quantum yields (PLQYs) of perovskite quantum dots (PQDs) in the violet are very lowest. This is an obstacle to the optical application of the...

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