to light conversion efficiency is still very limited. [15] In addition, nearly all commercial scintillators are prepared at high temperatures and pressures, which increases their cost and difficulty of preparation. [16,17] Furthermore, intrinsic rigidity cannot satisfy the increasing demand for flexible electronics. [18][19][20][21] In recent years, metal halide perovskites have been applied in X-ray sensors because of their high photoluminescence quantum yield (PLQY), strong absorption, long carrier diffusion length, defect tolerance, and environmentally friendly processing. [22][23][24][25] In addition, the soft nature of perovskites renders them potential candidates for the flexible integration of imaging sensors. [17,[25][26][27] To date, many novel techniques have been developed for preparing perovskite X-ray detectors. [28][29][30] Henning et al. employed inkjet printing to prepare flexible perovskite X-ray detectors. Advantages of this technology include high reproducibility and enhanced stability. [18] Huang et al. reported on perovskite-filled membranes for large-area detector arrays. [29] The good connectivity and crystallization of the perovskite crystals in the membrane create a flat surface, resulting in good imaging quality. Polymer-encapsulation can also be used to obtain flexible films for X-ray detectors, realizing stable and efficient X-ray detectors. Lead-free perovskite single crystals, such as Cs 2 AgBiBr 6 , Cs 3 Bi 2 I 9 , and Cs 3 Cu 2 I 5 , have also been applied for X-ray detections. [5,17,[31][32][33][34][35][36] However, the fabrication processes of high-quality scintillator films are usually complex, which might hinder their large-scale production. [37] Flexible scintillators are typically prepared by combining perovskite nanocrystal powders with polymers. [38][39][40][41] For example, Zeng et al. fabricated large-area films by adding CsPbBr 3 @Cs 4 PbBr 6 powder to a PS/toluene solution. [4] Liang et al. introduced BA 2 PbBr 4 :Mn(II) solid powders into polymethylmethacrylate (PMMA)/dichloromethane to realize a scintillator with high-resolution X-ray imaging. [42] In addition, Ma et al. and Mohammed et al. mixed (C 38 H 34 P 2 )MnBr 4 and Cs 3 Cu 2 I 5 powders with polydimethylsiloxane (PDMS), respectively, obtaining large-area flexible scintillator films. [43,44] However, all the above fabrication processes involve nanocrystal growth and powder grinding, resulting in powder agglomeration, long duration, and high cost. These drawbacks have hindered the industrial production of flexible scintillation films. Recently, Chen et al. and Hu et al. adopted an in situ method to fabricate high-quality flexible scintillator films (CsPbBr 3 and Environmentally friendly metal halides have emerged as emitters in lighting and X-ray imaging applications. However, the conventional scintillator fabrication process involves high-temperature sintering or powder grinding, resulting in large bulk crystals or agglomerates, which hamper flexible device integration and processability. Here, large-area flex...
All-inorganic perovskite nanocrystals (PNCs) have been anticipated to be used in efficient and stable perovskite optoelectronic devices because of their suitable bandgap, broad absorption spectrum, and high color purity. However, long-term stability remains a major obstacle for the commercial application of PNCs. In particular, for red-emissive perovskites, the reaction to the environment is more sensitive than that for the green counterpart, which makes a phase transformation easily occur at room temperature. On the basis of CsPbI3 PNCs, we analyze the main instability factors of red-emissive PNCs (620–720 nm), including their structures, optoelectronic properties, and instability mechanism. We then summarize some strategies to improve the stability and performance of the perovskites and light-emitting diodes (LEDs). Furthermore, we discuss the challenge of scaling up the production of PNCs. Finally, we propose possible perspectives for the development of perovskite materials.
and adjustable bandgap, thereby exhibiting extraordinary X-ray detection performance. [1] To date, high-quality lead-based perovskite single crystals have demonstrated ultrahigh detection performance. However, they are limited by their current shortcomings, including the toxicity of lead, chemical instability, inherent brittleness of bulk crystals, and their hightemperature fabrication and complex processes. [2] Therefore, the development of low-cost, environmentally friendly, flexible X-ray detectors, and novel scintillators still remain a challenge.Owing to the high emission stability, low self-absorption, soft lattice, unique self-trapped exciton emission (STE), [3] and relatively low toxicity and earth-abundant composition, lead-free copper-based halide Cs 3 Cu 2 I 5 nanocrystals (NCs) have attracted extensive attention in the field of optoelectronics, [4] such as electroluminescent lightemitting diode (LED) devices, [5] ultraviolet (UV) photodetectors, [6] X-ray imaging, [7] and anticounterfeiting technology. [8] Although progress has been made in the synthesis and application of Cs 3 Cu 2 I 5 NCs, [9] the insufficient synthesis reaction and difficulty in controlling the crystal size, morphology, and uniformity of Cs 3 Cu 2 I 5 NCs still remain the main obstacles hindering device performance and fundamental research. [10] Metal ion doping is an effective way to tune the structure and optoelectronic properties of materials, which Scintillators are essential for high-energy radiation detection in a variety of potential applications. However, due to complex fabrication processes and nanocrystal homogeneity, conventional scintillators are challenging to meet the need for cost-effective, environmentally friendly, and flexible X-ray detection. Here, monodisperse nanocrystals (NCs) with small grain size and colloidal stability are obtained by adjusting the doping concentration of Zn 2+ ions and controlling the morphology uniformity of Cs 3 Cu 2 I 5 NCs. The photoluminescence quantum yield (PLQY) for the optimal doping concentration is as high as 92.8%, which is a 28.5% improvement compared to nondoped NCs. Density functional theory calculations reveal that the Zn 2+ dopant inclines to occupy Cu sites and the I-rich condition suppresses the formation of I vacancy, enriching the excited electron density at the band-edge to enhance the self-trapped exciton emission. Moreover, high luminescence performance and flexible X-ray scintillator films are prepared using Zn 2+doped Cs 3 Cu 2 I 5 NCs, with a spatial resolution of up to 15.7 lp mm -1 . This work provides an effective strategy for the development of environmentally friendly, low-cost, and efficient blue-emitting 0D all-inorganic metal halides, as well as shows their great potential for high-performance flexible lead-free and low-toxicity X-ray detector applications.
Humic acids (HAs) have important environmental and geochemical effects on soil, water environments and sediment. HAs strongly complex some metal ions, which affects the migration of metal ions and the colloidal aggregation of HA. Here, the complexation of Ca2+ and Mg2+ with HA in aqueous solution under neutral conditions has been systematically studied by molecular dynamics (MD) simulation. The results show that the aggregation of HA is caused by the complexation of HA and metal ions, mainly due to the intermolecular bridging between Ca2+, Mg2+ and COO− groups. Monodentate and bidentate coordinations have been found between Ca2+ and COO− groups of different HA molecules in the same simulation system. Mg2+ only has a monodentate coordination with COO− group.
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