All-inorganic perovskite nanocrystals (NCs) have emerged as a new generation of low-cost semiconducting luminescent system for optoelectronic applications. The room-temperature photoluminescence quantum yields (PLQYs) of these NCs in the green and red spectral range approach unity. However, their PLQYs in the violet are much lower, and an insightful understanding of such poor performance remains missing. We report a general strategy for the synthesis of all-inorganic violet-emitting perovskite NCs with near-unity PLQYs through engineering local order of the lattice by nickel ion doping. A broad range of experimental characterizations, including steady-state and time-resolved luminescence spectroscopy, X-ray absorption spectra, and magic angle spinning nuclear magnetic resonance spectra, reveal that the low PLQY in undoped NCs is associated with short-range disorder of the lattice induced by intrinsic defects such as halide vacancies and that Ni doping can substantially eliminate these defects and result in increased short-range order of the lattice. Density functional theory calculations reveal that Ni doping of perovskites causes an increase of defect formation energy and does not introduce deep trap states in the band gap, which is suggested to be the main reason for the improved local structural order and near-unity PLQY. Our ability to obtain violet-emitting perovskite NCs with near-perfect properties opens the door for a range of applications in violet-emitting perovskite-based devices such as light-emitting diodes, single-photon sources, lasers, and beyond.

All-inorganic perovskites have emerged as a new class of phosphor materials owing to their outstanding optical properties. Zero-dimensional inorganic perovskites, in particular the CsPbBr-related systems, are inspiring intensive research owing to the high photoluminescence quantum yield (PLQY) and good stability. However, synthesizing such perovskites with high PLQYs through an environment-friendly, cost-effective, scalable, and high-yield approach remains challenging, and their luminescence mechanisms has been elusive. Here, we report a simple, scalable, room-temperature self-assembly strategy for the synthesis of CsPbBr/CsPbBr perovskite composites with near-unity PLQY (95%), high product yield (71%), and good stability using low-cost, low-toxicity chemicals as precursors. A broad range of experimental and theoretical characterizations suggest that the high-efficiency PL originates from CsPbBr nanocrystals well passivated by the zero-dimensional CsPbBr matrix that forms based on a dissolution-crystallization process. These findings underscore the importance in accurately identifying the phase purity of zero-dimensional perovskites by synchrotron X-ray technique to gain deep insights into the structure-property relationship. Additionally, we demonstrate that green-emitting CsPbBr/CsPbBr, combined with red-emitting KSiF:Mn, can be used for the construction of WLEDs. Our work may pave the way for the use of such composite perovskites as highly luminescent emitters in various applications such as lighting, displays, and other optoelectronic and photonic devices.

Cesium lead halide perovskite nanocrystals (NCs) have emerged as promising luminescent materials for a range of applications. However, the creation of highly luminescent violet-emitting CsPbCl3 NCs mostly relies on doping of a limited number of small-sized metal ions or post-synthetic surface treatment of NCs. Alkaline-earth (AE) metals (e.g., Ca2+, Sr2+, and Ba2+) have been proposed to be able to substitute Pb2+ in halide perovskites, yet it remains incompletely understood whether AE metal ions can be incorporated into the perovskite lattice or can be merely situated at the surface. Here, we explore the possibility of using AE metal ions for the suppression of the formation of trap centers, which leads us to develop a one-pot synthetic passivation strategy to boost the violet-emitting efficiency of CsPbCl3 NCs through the creation of a Ca2+/Sr2+ involved passivation layer. The photoluminescence quantum yield of violet emission reaches 77.1% by incorporating an optimal amount of Ca2+. A wide range of optical and structural characterizations, coupled with first-principles calculations, aid in clarifying the underlying mechanism for the AE-metal-dependent passivation of CsPbCl3 NCs. Specifically, based on the experimental and theoretical results, a model is proposed for the observed abnormal incorporation phenomenon of AE2+ ions in NCs (i.e., Ba2+ can be incorporated into the core of NCs, Ca2+/Sr2+ can only be at/near the surface, while Mg2+ can neither be in the core nor at the surface). We believe that the knowledge gained here may not only offer a new perspective to obtain high-efficiency violet-emitting perovskite NCs through a one-pot synthetic passivation but can also help elucidate the functions that AE2+ ions play in the optimization of perovskite optoelectronic devices.

Our results greatly deepen the understanding of the structural and photophysical properties of lanthanide-doped lead halide perovskite NCs.

All-inorganic perovskite nanocrystals (NCs) have emerged as a class of low-cost and high-efficiency light-emitting materials. However, the structure and phase transition behavior of these NCs remain poorly understood. Here, we provide unambiguous evidence that all these properties are associated with structural defects in NCs. Using CsPbCl 3 NCs as a model system, we find that the cubic subdomains in highly defective NCs gradually convert to the orthorhombic upon cooling room-temperature quasi-cubic NCs, whereas high-quality cousins, with mixed cubic and orthorhombic subdomains at room temperature, exhibit a significant resistance for such a phase transition. Car-Parrinello molecular dynamics simulations unveil the important role of point defects in triggering a stepwise, reversible phase transition of CsPbCl 3 NCs. Importantly, we show that the defect-triggered phase transition also exists in other all-inorganic perovskite NCs. Our findings provide new insight into the structure and phase transition of CsPbX 3 NCs and highlight the important role of defects in impacting these properties.

Zero-dimensional (0D) hybrid metal halides have emerged as a new generation of luminescent phosphors owing to their high radiative recombination rates, which, akin to their three-dimensional cousins, commonly demonstrate thermal quenching of luminescence. Here, we report on the finding of antithermal quenching of luminescence in 0D hybrid metal halides. Using (C 9 NH 20 ) 2 SnBr 4 single crystals as an example system, we show that 0D metal halides can demonstrate antithermal quenching of luminescence. A combination of experimental characterizations and first-principles calculations suggests that antithermal quenching of luminescence is associated with trap states introduced by structural defects in (C 9 NH 20 ) 2 SnBr 4 . Importantly, we find that antithermal quenching of luminescence is not only limited to (C 9 NH 20 ) 2 SnBr 4 but also exists in other 0D metal halides. Our work highlights the important role of defects in impacting photophysical properties of hybrid metal halides and may stimulate new efforts to explore metal halides exhibiting antithermal quenching of luminescence at higher temperatures.

It is extremely difficult to achieve hybrid halide perovskite semiconductors with luminescence at wavelengths longer than 1.0 μm, because of the inherent limitation of their band gaps. We show herein that solution-processable, Bi-activated, high-quality MAPbI3 films can be adopted as a new gain medium operating in the whole telecommunication window of 1260–1625 nm. Additionally, the structural and optical properties of Bi doped MAPbI3 have been investigated. The results indicate that the NIR PL originates from the structural defects induced by Bi. Finally, we accomplished optical amplification in the whole telecommunication window by using Bi-doped MAPbI3 films, which represents the first work where such a performance is attained among lead halide perovskites and Bi-doped photonic films. This work opens up exciting possibilities of using perovskite semiconducting materials as gain media for optical amplifiers and lasers operating in the telecommunication window

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