Low-dimensional metal halides have recently attracted extensive attention owing to their unique structure and photoelectric properties.H erein, we report the colloidal synthesis of all-inorganic low-dimensional cesium copper halide nanocrystals (NCs) by adopting ah ot-injection approach.U sing the same reactants and ligands,b ut different reaction temperatures,b oth 1D CsCu 2 I 3 nanorods and 0D Cs 3 Cu 2 I 5 NCs can be prepared. Density functional theory indicates that the reduced dimensionality in 1D CsCu 2 I 3 compared to 0D Cs 3 Cu 2 I 5 makes the excitons more localized, which accounts for the strong emission of 0D Cs 3 Cu 2 I 5 NCs. Subsequent optical characterization reveals that the highly luminescent, strongly Stokes-shifted broadband emission of 0D Cs 3 Cu 2 I 5 NCs arises from the self-trapped excitons.O ur findings not only present am ethod to control the synthesis of low-dimensional cesium copper halide nanocrystals but also highlight the potential of 0D Cs 3 Cu 2 I 5 NCs in optoelectronics. Scheme 1. Colloidal synthesis of cesium copper halide nanocrystals.Supportinginformation and the ORCID identification number for one of the authors of this article can be found under: https://doi.

Thermally activated delayed fluorescence (TADF) is generally observed in solid-state organic molecules or metalorganic complexes. However, TADF in all-inorganic colloidal nanocrystals (NCs) is rare. Herein, we report the first colloidal synthesis of an air-stable all-inorganic lead-free Cs 2 ZrCl 6 perovskite NCs. The Cs 2 ZrCl 6 NCs exhibit long-lived triplet excited state (138.2 ms), and feature high photoluminescence (PL) quantum efficiency (QY = 60.37 %) due to TADF mechanism. The emission color can be easily tuned from blue to green by synthesizing the mixed-halide Cs 2 ZrBr x Cl 6Àx (0 x 1.5) NCs. Femtosecond transient absorption and temperature dependent PL measurements are performed to clarify the emission mechanism. In addition, Bi 3+ ions are successfully doped into Cs 2 ZrCl 6 NCs, which further extends the PL properties. This work not only develops a new lead-free halide perovskite NCs for potential optoelectronic applications, but also offers unique strategies for developing new inorganic phosphors.

For display applications, it is highly desirable to obtain tunable red/green/blue emission. However, lead‐free perovskite nanocrystals (NCs) generally exhibit broadband emission with poor color purity. Herein, we developed a unique phase transition strategy to engineer the emission color of lead‐free cesium manganese bromides NCs and we can achieve a tunable red/green/blue emission with high color purity in these NCs. Such phase transition can be triggered by isopropanol: from one dimensional (1D) CsMnBr3 NCs (red‐color emission) to zero dimensional (0D) Cs3MnBr5 NCs (green‐color emission). Furthermore, in a humid environment both 1D CsMnBr3 NCs and 0D Cs3MnBr5 NCs can be transformed into 0D Cs2MnBr4⋅2 H2O NCs (blue‐color emission). Cs2MnBr4⋅2 H2O NCs could inversely transform into the mixture of CsMnBr3 and Cs3MnBr5 phase during the thermal annealing dehydration step. Our work highlights the tunable optical properties in single component NCs via phase engineering and provides a new avenue for future endeavors in light‐emitting devices.

All-inorganic zero-dimensional (0D) metal halides have recently received increasing attention due to their excellent photoluminescence (PL) performance and high stability. Herein, we present the successful doping of copper(I) into 0D Cs 2 ZnBr 4. The incorporating of Cu + cations enables the originally weakly luminescent Cs 2 ZnBr 4 to exhibit an efficient blue emission centered at around 465 nm, with a high photoluminescence quantum yield (PLQY) of 65.3 %. Detailed spectral characterizations, including ultrafast transient absorption (TA) techniques, were carried out to investigate the effect of Cu + dopants and the origin of blue emission in Cs 2 ZnBr 4 :Cu. To further study the role of the A-site cation and halogen, A 2 ZnCl 4 :Cu (A = Cs, Rb) were also synthesized and found to generate intense sky-blue emission (PLQY % 73.1 %). This work represents an effective strategy for the development of environmentally friendly, low-cost and high-efficiency blueemitting 0D all-inorganic metal halides. Low-dimensional metal halides have been widely studied as optoelectronic materials in the past two decades. [1] Zerodimensional (0D) metal halides have recently attracted intense interest due to their high photoluminescence quantum yields (PLQYs) and color tunability. [2] In terms of the 0D structure, various metal halide species, including tetrahedral BX 4 , pyramidal BX 5 , and octahedral BX 6 , have been reported to form highly crystalline materials. [3] Inspiringly, green, yellow and red luminescent 0D metal halides with high PLQYs have been realized in Cu-, Sn-, Sb-and In-based halide single crystals. [4] Nevertheless, blue-emitting 0D metal halides with high efficiency and stability remain challenging. Recently, several lead-free all-inorganic 0D metal halides with high efficient deep-blue emission in short wavelength blue light region (< 460 nm) have been reported. [5] However, all-inorganic 0D metal halides with intense emission in pureblue spectral region (460-480 nm), [6] which are more desirable for display and solid-state lighting, [7] remain largely unexplored. Therefore, it is of great significance to develop environmentally friendly, stable and high-efficiency 0D metal halides with PL peaks located at pure-blue region. Recent studies have demonstrated that doping is an effective strategy for the preparation of highly luminescent and stable metal halides. [8] Among the various alternatives, first row transition metals are of great interest as the majority are inexpensive, earth abundant, relatively nontoxic, and tend to form low-dimensional metal halides. [9] In this work, we chose Cs 2 ZnBr 4 as host and Cu + as the dopant for the 0D all-inorganic, stable, and efficient blueemitting metal halides. By introduction Cu + into the weakly luminescent Cs 2 ZnBr 4 (PLQY % 3.6 %, PL peak % 465 nm), an unprecedented improvement of PLQY (% 65.3 %) was realized without affecting the emission peak position. Detailed spectral characterizations including ultrafast transient absorption (TA) techniques reveal that the bright...

Low‐dimensional metal halides have recently attracted extensive attention owing to their unique structure and photoelectric properties. Herein, we report the colloidal synthesis of all‐inorganic low‐dimensional cesium copper halide nanocrystals (NCs) by adopting a hot‐injection approach. Using the same reactants and ligands, but different reaction temperatures, both 1D CsCu2I3 nanorods and 0D Cs3Cu2I5 NCs can be prepared. Density functional theory indicates that the reduced dimensionality in 1D CsCu2I3 compared to 0D Cs3Cu2I5 makes the excitons more localized, which accounts for the strong emission of 0D Cs3Cu2I5 NCs. Subsequent optical characterization reveals that the highly luminescent, strongly Stokes‐shifted broadband emission of 0D Cs3Cu2I5 NCs arises from the self‐trapped excitons. Our findings not only present a method to control the synthesis of low‐dimensional cesium copper halide nanocrystals but also highlight the potential of 0D Cs3Cu2I5 NCs in optoelectronics.

For inorganic semiconductor nanostructure, excitons in the triplet states are known as the "dark exciton" with poor emitting properties, because of the spin-forbidden transition. Herein, we report a design principle to boost triplet excitons photoluminescence (PL) in all-inorganic lead-free double-perovskite nanocrystals (NCs). Our experimental data reveal that singlet self-trapped excitons (STEs) experience fast intersystem crossing (80 ps) to triplet states. These triplet STEs give bright green color emission with unity PL quantum yield (PLQY). Furthermore, efficient energy transfer from triplet STEs to dopants (Mn 2+ ) can be achieved, which leads to white-light emitting with 87% PLQY in both colloidal and solid thin film NCs. These findings illustrate a fundamental principle to design efficient white-light emitting inorganic phosphors, propelling the development of illuminationrelated applications.

Lead-free halide double perovskites (DPs) have attracted great attention due to their stability, nontoxicity and good photophysical property. In this work, we report a new, small-bandgap Cs2CuSbCl6 DP nanocrystals (NCs) with a bandgap of 1.66 eV, which is the smallest bandgap in reported lead-free three-dimensional DP NCs. Density functional theory calculations confirm that Cs2CuSbCl6 DP has an indirect bandgap of 1.70 eV, in good agreement with the experimental result. The photophysical property of Cs2CuSbCl6 NCs is studied by the combination of femtosecond transient absorption (TA) and nanosecond TA techniques. In addition, the Cs2CuSbCl6 NCs exhibit good stability exposed in the air. These results show that these NCs will have great potential to be used as a light-absorbing material for photovoltaic applications.

Triplet exciton‐based long‐lived phosphorescence is severely limited by the thermal quenching at high temperature. Herein, we propose a novel strategy based on the energy transfer from triplet self‐trapped excitons to Mn2+ dopants in solution‐processed perovskite CsCdCl3. It is found the Mn2+ doped hexagonal phase CsCdCl3 could simultaneously exhibit high emission efficiency (81.5 %) and long afterglow duration time (150 s). Besides, the afterglow emission exhibits anti‐thermal quenching from 300 to 400 K. In‐depth charge‐carrier dynamics studies and density functional theory (DFT) calculation provide unambiguous evidence that carrier detrapping from trap states (mainly induced by Cl vacancy) to localized emission centers ([MnCl6]4−) is responsible for the afterglow emission with anti‐thermal quenching. Enlightened by the present results, we demonstrate the application of the developed materials for optical storage and logic operation applications.