Halide Nanocrystals Research Articles

Continuous nanomanufacturing of Mn2+-doped inorganic lead halide nanocrystals with high-concentration precursors

Microscale flow synthesis is a prominent large-scale method for producing inorganic perovskite nanocrystals (NCs), yet its application in one-pot synthesis of Mn-doped NCs is rare. Here, an optimized microscale flow method is used to prepare Mn2+-doped CsPb(Cl/Br)3 NCs by increasing the cesium precursor concentration to 25 mmol/L to improve the synthesis efficiency. The photoluminescence quantum yield of Mn2+ ions emission exhibits an enhancement with reaction temperature, reaching 39 % at 200 °C. Additionally, high-concentration precursors favor obtaining superior photoluminescence properties at a higher reaction temperature. There is a disparity in the shape of the NCs obtained at 100 and 200 °C, presumably due to the existence of extra rhombohedral phase. The molar ratio of Mn-to-Pb influences the emission characteristics of these NCs, with an optimal value of 3:1 under the above two reaction temperatures. These Mn2+-doped NCs possess promising applications in LEDs and anti-counterfeiting patterns, and the Mn2+ ions emission has remarkable resistance when exposed to oxygen. Furthermore, these NCs may also serve as probes for higher temperatures (>80 °C).

Near‐Unity Green Luminescent and Stable Lead‐Free Cs3Cu2Cl5 Nanocrystals Assisted by MnC2O4 Treatment

AbstractThe toxicity and chemical instability shortcomings of lead halide perovskites are major concerns that continue to motivate the search for next generation alternatives. Copper halides are known to be lead‐free, earth‐abundant, low‐cost, and environmentally friendly, and affordable in optoelectronic performance due to their bright luminescence, tunable emission wavelength, and excellent stability. However, the controlled synthesis of low‐dimensional copper halide nanocrystals (NCs) with near‐unity photoluminescence quantum yield (PLQY) and high stability remains a great challenge. In this work, we report a reasonable optimization approach for the preparation of Cs3Cu2Cl5 NCs by hot‐injection colloidal synthesis technology. Specifically, the Cs3Cu2Cl5 NCs synthesized with MnC2O4 as the defect repair agent exhibited negligible self‐absorption, bright green luminosity with PL emission at about 535 nm and PLQY can be increased from 68.7 % to 100 %. The Cs3Cu2Cl5 NCs shows excellent stability and outstanding optical properties, and is expected to be used as highly efficient green light emitter in high‐efficiency X‐ray scintillator.

Uncovering the Effect of A-Site Cations on Localized Excitons Photoluminescence of Manganese-Doped Zinc Chloride Nanocrystals.

Elucidating the key factors that affect the localized excitons (LEs) photoluminescence (PL) in lead-free metal halide nanocrystals (NCs) is important for their optoelectronic applications. However, the effect of A-site cations on LEs based PL is not well understood. Herein, we varied the A-site cation ratio (Rb/Cs) to investigate the influence on LEs based PL in manganese-doped zinc chloride NCs. Through time-resolved photoluminescence (TR-PL) spectra and density functional theory (DFT) calculations, we discovered that Cl vacancy is energetically more favorable in Mn2+-doped Rb3ZnCl5 NCs compared to Mn2+-doped Cs3ZnCl5 NCs. The higher concentration of Cl vacancy increases the nonradiative recombination process in Rb3ZnCl5:Mn2+ NCs, ultimately determining the PL efficiency. This research enhances the understanding of the A-site cation effect on LEs-based PL in lead-free metal halide NCs.

Exploring Light Harvesting in Blends of Cesium Lead Halide Nanocrystals with Fullerene Derivatives

Exploring Light Harvesting in Blends of Cesium Lead Halide Nanocrystals with Fullerene Derivatives

Disorder and Halide Distributions in Cesium Lead Halide Nanocrystals as Seen by Colloidal 133Cs Nuclear Magnetic Resonance Spectroscopy.

Colloidal nuclear magnetic resonance (cNMR) spectroscopy on inorganic cesium lead halide nanocrystals (CsPbX3 NCs) is found to serve for noninvasive characterization and quantification of disorder within these structurally soft and labile particles. In particular, we show that 133Cs cNMR is highly responsive to size variations from 3 to 11 nm or to altering the capping ligands on the surfaces of CsPbX3 NCs. Distinct 133Cs signals are attributed to the surface and core NC regions. Increased heterogeneous broadening of 133Cs signals, observed for smaller NCs as well as for long-chain zwitterionic capping ligands (phosphocholines, phosphoethanol(propanol)amine, and sulfobetaines), can be attributed to more significant surface disorder and multifaceted surfaces (truncated cubes). On the contrary, capping with dimethyldidodecylammonium bromide (DDAB) successfully reduces signal broadening owing to better surface passivation and sharper (001)-bound cuboid shape. DFT calculations on various sizes of NCs corroborate the notion that the surface disorder propagates over several octahedral layers. 133Cs NMR is a sensitive probe for studying halide gradients in mixed Br/Cl NCs, indicating bromide-rich surfaces and chloride-rich cores. On the contrary, mixed Br/I NCs exhibit homogeneous halide distributions.

Surfactant-Assisted Synthesis of Hybrid Copper(I) Halide Nanocrystals for X-ray Scintillation Imaging

Surfactant-Assisted Synthesis of Hybrid Copper(I) Halide Nanocrystals for X-ray Scintillation Imaging

Tunable white light emission in antimony doped vacancy-ordered double perovskite Cs2ZrCl6 nanocrystals

Design of stable white-light emitting materials based on the emerging lead-free metal halide colloidal nanocrystals is in urgent demand for lighting technology innovation. Herein, we developed a facile hot-injection method and optimize the synthesis conditions to prepare Sb3+ doped Cs2ZrCl6 nanocrystals with good uniformity and crystallinity. Sb3+ ions were doped into the Cs2ZrCl6 lattice and proved to occupy the sites of Zr4+ ions, generating additional absorption bands at lower energy and new emission band centered at 620 nm apart from the absorption and emission from the host. The emission at 620 nm from Sb3+ ions could be prompted by an energy transfer process between the host STEs and Sb3+ ions. Moreover, benefiting from two broad emission bands from singlet and triplet states of Sb3+ ions in Cs2ZrCl6 nanocrystals, we obtained tunable white-light-emitting nanocrystals by adjusting the dopant concentration. Our study provides a reliable method to design efficient single-emitter-based white-light emitting metal halide nanocrystals and promote their development in the field of lighting and displays.

Alkylammonium Halides for Phase Regulation and Luminescence Modulation of Cesium Copper Iodide Nanocrystals for Light-Emitting Diodes.

All-inorganic cesium copper halide nanocrystals have attracted extensive attention due to their cost-effectiveness, low toxicity, and rich luminescence properties. However, controlling the synthesis of these nanocrystals to achieve a precise composition and high luminous efficiency remains a challenge that limits their future application. Herein, we report the effect of oleylammonium iodide on the synthesis of copper halide nanocrystals to control the composition and phase and modulate their photoluminescence (PL) quantum yields (QYs). For CsCu2I3, the PL peak is centered at 560 nm with a PLQY of 47.3%, while the PL peak of Cs3Cu2I5 is located at 440 nm with an unprecedently high PLQY of 95.3%. Furthermore, the intermediate-state CsCu2I3/Cs3Cu2I5 heterostructure shows white light emission with a PLQY of 66.4%, chromaticity coordinates of (0.3176, 0.3306), a high color rendering index (CRI) of 90, and a correlated color temperature (CCT) of 6234 K, indicating that it is promising for single-component white-light-emitting applications. The nanocrystals reported in this study have excellent luminescence properties, low toxicity, and superior stability, so they are more suitable for future light-emitting applications.

Bright Blue Emission Lead-Free Halides with Narrow Bandwidth Enabled by Oversaturated Europium Doping.

Eu2+-based lead-free metal halide nanocrystals (LFMH NCs), including CsEuCl3 NCs and CsX:Eu2+ NCs (X = Cl or Br), exhibit highly efficient narrow-band blue photoluminescence, making them competitive candidates for next-generation lighting and displays. However, the growing mechanism of the aforementioned NCs lacks in-depth study, which hinders the development of Eu2+-based nanomaterials. Herein, we demonstrate the colloidal synthesis of CsBr:Eu2+ NCs based on an air-stable europium source. The NCs show deep blue photoluminescence centered at 444 nm, with a maximum photoluminescence quantum yield (PLQY) reaching 53.4% and a fwhm of 30 nm. We further reveal the mechanism that determines CsBr host growth and Eu2+ doping in CsBr:Eu2+ nanocrystals, especially dopant trapping and self-purification, that determine the PLQY level. Pure white, warm white, and cold white LEDs are fabricated based on CsBr:Eu2+ NCs, red and green phosphors, and their performance suits the needs of high-quality lighting.

Biocompatible Silica-Coated Europium-Doped CsPbBr3 Nanoparticles with Luminescence in Water for Zebrafish Bioimaging.

Cesium lead halide (CsPbX3, X = Br, Cl, and I) nanocrystals (NCs) are widely concerned and applied in many fields due to the excellent photoelectric performance. However, the toxicity of Pb and the loss of luminescence in water limit its application in vivo. A stable perovskite nanomaterial with good bioimaging properties is developed by incorporating europium (Eu) in CsPbX3 NCs followed with the surface coating of silica (SiO2) shell (CsPbX3:Eu@SiO2). Through the surface coating of SiO2, the luminescence stability of CsPbBr3 in water is improved and the leakage of Pb2+ is significantly reduced. In particular, Eu doping inhibits the photoluminescence quantum yield reduction of CsPbBr3 caused by SiO2 coating, and further reduces the release of Pb2+. CsPbBr3:Eu@SiO2 nanoparticles (NPs) show efficient luminescence in water and good biocompatibility to achieve cell imaging. More importantly, CsPb(ClBr)3:Eu@SiO2 NPs are obtained by adjusting the halogen components, and green light and blue light are realized in zebrafish imaging, showing good imaging effect and biosafety. The work provides a strategy for advanced perovskite nanomaterials toward biological practical application.

Harnessing laser technology to create stable metal halide perovskite-rGO conjugates as promising electrodes for Zn-ion capacitors.

We report that the direct conjugation of metal halide perovskite nanocrystals on rGO sheets can provide high performance and stable electrodes for Zn-ion capacitors. It is the first time that metal halide nanocrystals have been used to enhance the energy storage of 2D materials in capacitors by introducing an additional pseudocapacitance mechanism. In particular, we present a simple, rapid and room temperature laser-induced method to anchor CsPbBr3 nanocrystals on rGO sheets without affecting the initial morphology and crystal structure of the two components. The flexible and high surface area of the rGO sheets enables the conjugation of individual metal halide perovskite nanocrystals, giving rise to new synergetic functionalities. As a result, the specific capacitance of the perovskite-rGO conjugated electrodes can be enhanced by 178- and 152-times compared to those of the plain rGO and perovskite electrodes respectively.

Metal co-doped cesium manganese chlorine nanocrystals with high efficiency and tunable red emission

Metal co-doped cesium manganese halide nanocrystals are synthesized to enhance the red emission depending on the transitional role of Tm3+ ions, and realize tunable red emission from 660 nm to 628 nm by controlling the Pb doping contents.

Nickel(II)-Doped Lead-Free Halide Crystals Exhibiting Highly Efficient Tunable Blue-Emitting out of Antiferromagnetic Ni-Ni Coupling.

Metal halide crystals are widely used in optoelectronic fields due to their excellent optical properties. The hunt for a lead-free halide semiconductor with superior optical performance is a particularly fascinating topic in order to avoid the toxicity of lead. Here, we incorporate Ni2+ into a series of halide nanocrystals (NCs) through solution-phase synthesis. By modifying the A-site and varying the halide compositions, we successfully achieved significant tunability of the blue emission of the Ni2+-doped AX (A = K+, Rb+, NH2CH = NH2+ (FA), CH3NH3+ (MA); X = Br, I) NCs, ranging from 375 to 490 nm, due to the antiferromagnetic polaron (AMP), which is in contrast with the excitonic magnetic polarons (EMP) from those with ferromagnetic (FM) coupling between transition metal ions in similar compounds. This work shows that Ni2+-doped halide crystals could become a typical example providing AMP excitation as the optional emission centers for use in light emitting devices.

Metal Halide Nanocrystals@Silica Aerogel Composite with Enhanced Dispersion Stability and Light Output for Efficient X-Ray Imaging in Harsh Environment.

Metal halide nanocrystals (MHNCs) embedded in a polymer matrix as flexible X-ray detector screens is an effective strategy with the advantages of low cost, facile preparation, and large area flexibility. However, MHNCs easily aggregate during preparation, recombination, under mechanical force, storage, or high operating temperature. Meanwhile, it shows an unmatched refractive index with polymer, resulting in low light yield. The related stability and properties of the device remain a huge unrevealed challenge. Herein, a composite screen (CZBM@AG-PS) by integrating MHNCs (Cs2ZnBr4: Mn2+ as an example) into silica aerogel (AG) and embedded in polystyrene (PS) is successfully developed. Further characterization points to the high porosity AG template that can effectively improve the dispersion of MHNCs in polymer detector screens, essentially decreasing nonradiative transition, Rayleigh scattering, and performance aging induced by aggregation in harsh environments. Furthermore, the higher light output and lower optical crosstalk are also achieved by a novel light propagation path based on the MHNCs/AG and AG/PS interfaces. Finally, the optimized CZBM@AG-PS screen shows much enhanced light yield, spatial resolution, and temperature stability. Significantly, the strategy is proven universal by the performance tests of other MHNCs embedded composite films for ultra-stable and efficient X-ray imaging.

Sb-Doped Cs3 TbCl6 Nanocrystals for Highly Efficient Narrow-Band Green Emission and X-Ray Imaging.

Metal halide nanocrystals (NCs) with high photoluminescence quantum yield (PLQY) are desirable for lighting, display, and X-ray detection. Herein, the novel lanthanide-based halide NCs are committed to designing and optimizing the optical and scintillating properties, so as to unravel the PL origin, exciton dynamics, and optoelectronic applications. Sb-doped zero-dimensional (0D) Cs3 TbCl6 NCs exhibit a green emission with a narrow full width of half maximum of 8.6nm, and the best PLQY of 48.1% is about three times higher than that of undoped NCs. Experiments and theoretical calculations indicate that 0D crystalline and electronic structures make the exciton highly localized on [TbCl6 ]3- octahedron, which boosts the Cl- -Tb3+ charge transfer process, thus resulting in bright Tb3+ emission. More importantly, the introduction of Sb3+ not only facilitates the photon absorption transition, but also builds an effective thermally boosting energy transfer channel assisted by [SbCl6 ]3- -induced self-trapped state, which is responsible for the PL enhancement. The high luminescence efficiency and negligible self-absorption of the Cs3 TbCl6 : Sb nanoscintillator enable a more sensitive X-ray detection response compared with undoped sample. The study opens a new perspective to deeply understand the excited state dynamics of metal halide NCs, which helps to design high-performance luminescent lanthanide-based nanomaterials.

Bright Transparent Scintillators with High Fraction BaCl2 : Eu2+ Nanocrystals Precipitation: An Ionic-Covalent Hybrid Network Strategy toward Superior X-Ray Imaging Glass-Ceramics.

Metal halide crystals are bright but hygroscopic scintillator materials that are widely used in X-ray imaging and detectors. Precipitating them in situ in glass to form glass ceramics (GCs) scintillator offers an efficient avenue for large-scale preparation, high spatial resolution, and excellent stability. However, precipitating a high fraction of metal halide nanocrystals in glass to maintain high light yield remains a challenge. Herein, an ionic-covalent hybrid network strategy for constructing GCs scintillator with high crystallinity (up to ≈37%) of BaCl2 : Eu2+ nanocrystals is presented. Experimental data and simulations of glass structure reveal that the Ba2+ -Cl- clustering promotes the high crystallization of BaCl2 nanocrystals. The ultralow phonon energy (≈200 cm-1 ) of BaCl2 nanocrystals and good Eu reduction effect enable high photoluminescence inter quantum efficiency (≈80.41%) in GC. GCs with varied crystallinity of BaCl2 : Eu2+ nanocrystals demonstrate efficient radioluminescence and tunable scintillator performance. They either outperform Bi4 Ge3 O14 single crystal by over 132% steady-state light yield or provide impressive X-ray imaging resolutions of 20 lp mm-1 . These findings provide a new design strategy for developing bright transparent GCs scintillators with a high fraction of metal halide nanocrystals for X-ray high-resolution imaging applications.

Efficient and Selective Photogeneration of Stable N-Centered Radicals via Controllable Charge Carrier Imbalance in Cesium Lead Halide Nanocrystals.

Despite the versatility of semiconductor nanocrystals (NCs) in photoinduced chemical processes, the generation of stable radicals has been more challenging due to reverse charge transfer or charge recombination even in the presence of sacrificial charge acceptors. Here, we show that cesium lead halide (CsPbX3) NCs can selectively photogenerate either aminium or aminyl radicals from amines, taking advantage of the controllable imbalance of the electron and hole populations achieved by varying the solvent composition. Using dihalomethane as the solvent, irreversible removal of the electrons from CsPbX3 NCs enabled by the photoinduced halide exchange between the NCs and the dihalomethane resulted in efficient oxidative generation of the aminium radical. In the absence of dihalomethane in solvent, the availability of both electrons and holes resulted in the production of an aminyl radical via sequential hole transfer and reductive N-H bond dissociation. The negative charge of the halide ions on the NC's lattice surface appears to facilitate the aminyl radical production, competing favorably with the reversible charge transfer reverting to the reactant.

Size-dependent miscibility controls the kinetics of anion exchange in cesium lead halide nanocrystals.

Anion exchange is a facile, post-synthetic method to tune the emission wavelength of colloidal cesium lead halide (CsPbX3, X = Cl, Br, I) perovskite nanocrystals. While colloidal nanocrystals can exhibit size-dependent phase stability and chemical reactivity, the role of size in the mechanism of anion exchange in CsPbX3 nanocrystals has not been elucidated. We used single-particle fluorescence microscopy to monitor the transformation of individual CsPbBr3 nanocrystals to CsPbI3. By systematically varying the size of the nanocrystals and the concentration of substitutional iodide, we observed that smaller nanocrystals exhibit longer transition times in their fluorescence trajectories, while larger nanocrystals undergo a more abrupt transition during anion exchange. Monte Carlo simulations were used to rationalize the size-dependent reactivity, in which we varied how each exchange event affects the probability for further exchange. Greater cooperativity for simulated ion exchange leads to shorter transition times to complete the exchange. We propose that size-dependent miscibility between CsPbBr3 and CsPbI3 at the nanoscale controls the reaction kinetics. Smaller nanocrystals maintain a homogeneous composition during anion exchange. As the nanocrystal size increases, variations in the octahedral tilting patterns of the perovskite crystals lead to different structures for CsPbBr3 and CsPbI3. Thus, an iodide-rich region must first nucleate within larger CsPbBr3 nanocrystals, which is followed by rapid transformation to CsPbI3. While higher concentrations of substitutional anions can suppress this size-dependent reactivity, the inherent differences in reactivity between nanocrystals of different sizes are important to consider when scaling up this reaction for applications in solid-state lighting and biological imaging.

The Dark Side of Lead-Free Metal Halide Nanocrystals: Substituent-Modulated Photocatalytic Activity in Benzyl Bromide Reduction.

We illustrate here the high photocatalytic activity of sustainable lead-free metal halide nanocrystals (NCs), namely, Cs3Sb2Br9 NCs, in the reduction of p-substituted benzyl bromides in the absence of a cocatalyst. The electronic properties of the benzyl bromide substituents and the substrate affinity to the NC surface determine the selectivity in C-C homocoupling under visible light irradiation. This photocatalyst can be reused for at least three cycles and preserves its good performance with a turnover number of ca. 105,000.

Unveiling the Localized Exciton-Based Photoluminescence of Manganese Doped Cesium Zinc Halide Nanocrystals

Lead-free metal halide nanocrystals (NCs) have aroused increasing attention due to their unique optoelectronic properties based on localized excitons (LEs). However, the vital influencing factors for the LEs based photoluminescence (PL) are still not well-understood due to the coupling of various intrinsic and extrinsic factors of the NCs. Herein, by engineering the phase, size, morphology, and chemical composition, we are able to decouple the intrinsic and extrinsic factors of manganese doped cesium zinc-halide NCs. We found both the intrinsic metal-halide coordination field and the extrinsic crystal defects have significant influences on the LEs' recombination and energy transfer processes, and hence determine the PL efficiency. Unlike for the free excitons (FEs) based PL, the phase as well as the crystal morphology do not play major roles for the LEs based PL. This work provides a new insight for the study of LE dynamics of metal halide NCs.