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Transformation of the Anion Sublattice in the Cation-Exchange Synthesis of Au <sub/>2</sub> S from Cu <sub/>2-x</sub> S Nanocrystals
摘要： Cation exchange is a versatile post-synthetic technique that has been exploited in the synthesis of metastable nanocrystals through preservation of the anion sublattice. Here we report on the mechanistic details of the synthesis of metastable Au2S via cation exchange with Cu2-xS nanocrystals. This conversion requires a transformation of the anion sublattice, from hcp in Cu2-xS to bcc Au2S accompanied by an expansion of the unit cell. The ligand environment plays a key role in the driving force of the reaction as the presence of oleylamine allows the conversion to proceed at room temperature while the addition of trioctylphosphine hinders the reaction. By employing transmission electron microscopy (TEM) on faceted nanocrystals and partial cation exchange of nanocrystals, it was demonstrated that the reaction proceeds in a highly directional manner through the pyramidal facets. Since cation exchange produces high quality nanocrystals as seen through XRD and TEM, UV-Vis and Raman spectroscopy were used to characterize the optoelectronic properties of the metastable Au2S nanocrsytals. A Tauc plot analysis revealed a band gap of 2.6 eV, while two intrinsic Raman modes were identified at 265 cm-1 and 329 cm-1. Density functional theory (DFT) calculations of structures, energy bands, optical spectra, and phonon spectra were performed and combined with the experimental data to provide additional insights into the characterization of Au2S nanocrystals.
关键词： XRD,Raman spectroscopy,UV-Vis,trioctylphosphine,nanocrystals,TEM,Cation exchange,DFT,Cu2-xS,anion sublattice transformation,Au2S,oleylamine
更新于2025-09-09 09:28:46
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Lead-Free Direct Bandgap Double Perovskite Nanocrystals with Bright Dual-Color Emission
摘要： Lead-free double perovskite nanocrystals (NCs), i.e. Cs2AgInxBi1?xCl6 (x = 0, 0.25, 0.5 0.75 and 0.9), that can be tuned from the indirect bandgap (x = 0, 0.25 and 0.5) to the direct bandgap (x = 0.75 and 0.9) are designed. Direct-bandgap NCs exhibit 3 times greater absorption cross-section, lower sub-bandgap trap states, and >5 times photoluminescence quantum efficiency (PLQE) compared with those observed for indirect bandgap NCs (Cs2AgBiCl6). A PLQE of 36.6% for direct bandgap NCs is comparable to those observed for lead-perovskite NCs in the violet region. Besides the band edge violet emission, the direct bandgap NCs exhibit bright orange (570 nm) emission. Density functional theory calculations suggesting forbidden transition is responsible for the orange emission, which is supported by time resolved PL and PL excitation spectra. The successful design of lead-free direct bandgap perovskite NCs with superior optical properties opens the door for high performance lead-free perovskite optoelectronic devices.
关键词： dual-color emission,direct bandgap,Lead-free,photoluminescence quantum efficiency,double perovskite nanocrystals
更新于2025-09-09 09:28:46
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[IEEE 2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS) - Odessa, Ukraine (2018.9.4-2018.9.7)] 2018 9th International Conference on Ultrawideband and Ultrashort Impulse Signals (UWBUSIS) - Study of Raman Spectra of Pb<inf>3</inf>(P<inf>0.5</inf> V<inf>0.5</inf>O<inf>4</inf>)<inf>2</inf>Crystallized in Nanoscale Opal Pores
摘要： The results of Raman spectra investigation of dielectric Pb3(Р0.5V0.5О4)2 crystallized in pores of synthetic opal are presented. The comparative analysis of these spectra with Raman spectra of Pb3(Р0.5V0.5О4)2 in the monocrystalline state is carried out. Due to fitting o the spectra it was possible to reveal the changes in position of the spectral lines and their half-widths. It was shown that these effects may be caused by changing in the lengths of bonds inside the Pb3(Р0.5V0.5О4)2 molecule as a result of crystallization in nano-sized pores of synthetic opal.
关键词： synthetic opals,Raman spectra,lead phosphate-vanadate,photonic crystals,nanocrystals
更新于2025-09-09 09:28:46
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Direct synthesis of high-quality perovskite nanocrystals on a flexible substrate and deterministic transfer
摘要： Solid-state perovskite nanocrystals are promising coherent light sources, as there is optical feedback within the crystal structure. In order to utilize the high performance of perovskites for on-chip applications, or observe new physical phenomena, these crystals must be integrated with pre-fabricated electronic or photonic structures. However, the material’s fragility has made the deterministic transfer a great challenge thus far. Here, we report the first deterministic transfer of perovskite nanocrystals with sub-micron accuracy. Cesium lead halide (CsPbI3) nanocrystals were directly synthesized on flexible polydimethylsiloxane (PDMS) stamps via chemical vapor deposition (CVD) and subsequently transferred onto arbitrary substrates/structures. We demonstrated the transfer of a CsPbI3 crystalline nanoplate (NP) onto an 8 μm fiber core and achieved single-mode whispering gallery mode lasing. Our method can be extended to a variety of other arbitrary substrates (e.g., electrodes, photonic structures, micromechanical systems), laying the foundations for previously unattainable opportunities in perovskites-based devices.
关键词： CsPbI3 nanocrystals,PDMS substrate,CVD,Deterministic transfer
更新于2025-09-09 09:28:46
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Synthesis of Curved CuIn1-xGax(S1-ySey)2 Nanocrystals and Complete Characterization of their Diffraction Contrast Effects
摘要： Herein, we report the synthesis and complete structural characterization of curved CuIn1-xGax(S1-ySey)2 (x = y = 0.5) nanocrystals, which adopt a 2D nanoplate morphology and crystallize in the hexagonal wurtzite phase. A detailed transmission electron microscopy (TEM) analysis reveals that the 2D nanoplates are predominately [001]-oriented and exhibit a unique bend contour pattern, due to curvature on the (001) basal plane. The contrast behavior of bend contours in this system is further supported through specimen tilting experiments inside the TEM, in combination with dark-field (DF) imaging in both TEM and scanning TEM (STEM) modes. This bending is believed to originate from the proximity effect of the top and bottom (001) surfaces.
关键词： bend contours,CuIn1-xGax(S1-ySey)2,hexagonal wurtzite phase,TEM,nanocrystals
更新于2025-09-09 09:28:46
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Mixed Surface Chemistry: An Approach to Highly Luminescent Biocompatible Amphiphilic Silicon Nanocrystals.
摘要： Amphiphilic nanoparticles (AP-NPs) are attractive for many far-reaching applications in diverse sectors. Amphiphilic silicon nanocrystals (AP-SiNCs) are particularly promising for luminescence-based bioimaging, biosensing, and drug delivery due to their size- and surface chemistry-dependent photoluminescence, high photoluminescence quantum yield, long-term photostability, and robustness to bioconjugation. Numerous studies demonstrated the synthesis of high quality SiNCs that are compatible with organic solvents. However, preparing water-soluble SiNCs while maintaining their attractive PL properties is very challenging and to date, only one report of blue-emitting amphiphilic silicon nanocrystals (AP-SiNCs) has appeared. This report outlines a straightforward one-step thermal hydrosilylation approach that affords AP-SiNCs soluble in aqueous media in high concentrations (i.e., 14.4 mg/mL silicon core-based), exhibit bright long-lived photoluminescence in the red/near-infrared spectral region, are biocompatible, and present bio-conjugable surface groups.
关键词： Drug delivery,Photoluminescence,Silicon nanocrystals,Biosensing,Bioimaging,Amphiphilic nanoparticles
更新于2025-09-09 09:28:46
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Aqueous synthesis of lead halide perovskite nanocrystals with high water stability and bright photoluminescence
摘要： Lead halide perovskites nanocrystals (NCs) have attracted intense attentions because of their excellent optoelectronic properties. The ionic nature of halide perovskites makes them highly vulnerable to water. Encapsulation of perovskite NCs with inorganic or organic materials have been reported to enhance the stability, however they often suffer from large aggregation size, low water-solubility and difficulty for further surface functionalization. Here, we report a facile aqueous process to synthesize water-soluble CsPbBr3/Cs4PbBr6 NCs with the assistance of fluorocarbon agent, which features a novel mechanism of the perovskite crystallization at oil/water interface and direct perovskite NCs/fluorocarbon agent self-assembly in aqueous environment. The products exhibit a high absolute photoluminescence quantum yield (PLQY) of ~80% in water with the photoluminescence lasting for weeks. Through successive ionic layer adsorption and reaction (SILAR), BaSO4 was further applied to encapsulate the NCs, and greatly enhanced their stability in phosphate buffered saline solutions. The high stability in water and saline solution, high PLQY and tunable emission wavelength, together with the successful demonstration of brain tissue labelling and photoluminescence under X-ray excitation, make our perovskite NCs a promising choice for X-ray fluorescent bio-labels.
关键词： CsPbBr3,water soluble,multicolor,perovskite,nanocrystals
更新于2025-09-09 09:28:46
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Rationalizing and Controlling the Surface Structure and Electronic Passivation of Cesium Lead Halide Nanocrystals
摘要： Colloidal lead halide perovskite nanocrystals (NCs) have recently emerged as versatile photonic sources. Their processing and luminescent properties are challenged by the lability of their surfaces, i.e. the interface of the NC core and the ligand shell. On the example of CsPbBr3 NCs, we model the nanocrystal surface structure and its effect on the emergence of trap states using density functional theory. We rationalize the typical observation of a degraded luminescence upon aging or the luminescence recovery upon post-synthesis surface treatments. The conclusions are corroborated by the elemental analysis. We then propose a strategy for healing the surface trap states and for improving the colloidal stability by the combined treatment with didodecyldimethyl ammonium bromide and lead bromide and validate this approach experimentally. This simple procedure results in robust colloids, which are both highly pure and exhibit high photoluminescence quantum yields of up to 95-98%, retained even after 3-4 rounds of washing.
关键词： trap states,didodecyldimethyl ammonium bromide,luminescence recovery,photoluminescence quantum yields,lead bromide,CsPbBr3 NCs,density functional theory,Colloidal lead halide perovskite nanocrystals,surface structure
更新于2025-09-09 09:28:46
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Trap-Mediated Two-Step Sensitization of Manganese Dopants in Perovskite Nanocrystals
摘要： Halide perovskite nanocrystals hold promise for printable optoelectronic and photonic applications. Doping enhances their functionalities and is being investigated for substituting lead with environmentally friendlier elements. The most investigated dopant is Mn2+ that acts as a color center sensitized by the host excitons. The sensitization mechanism is far from understood and no comprehensive picture of the energy-transfer process has been proposed. Similarly, the role of shallow states - particularly abundant in defect tolerant materials - is still unknown. Here, we address this problem via spectroscopic studies at controlled excitation density and temperature on Mn:CsPbCl3 nanocrystals. Our results indicate a two-step process involving exciton localization in a shallow metastable state that mediates the thermally-assisted sensitization of the Mn2+-emission, which is completely quenched for T<200K. At T≤60K, however, such emission surprisingly reappears, suggesting direct energy-transfer from band-edge states. Electron spin resonance supports this picture revealing the signatures of conformational rearrangements below 70K, possibly removing the potential barrier for sensitization. Our results demystify anomalous behaviors of the exciton-to-Mn2+ energy-transfer mechanism and highlight the role of shallow defects in the photophysics of doped perovskite nanostructures.
关键词： Halide perovskite nanocrystals,energy-transfer,spectroscopic studies,Mn2+ dopants,shallow states
更新于2025-09-09 09:28:46
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AIP Conference Proceedings [Author(s) 6TH INTERNATIONAL CONFERENCE ON PRODUCTION, ENERGY AND RELIABILITY 2018: World Engineering Science & Technology Congress (ESTCON) - Kuala Lumpur, Malaysia (13–14 August 2018)] - Characterization of tin oxide (SnO2) nanostructures prepared by thermal oxidation
摘要： Tin oxide (SnO2) nanocrystals and nanowires were successfully synthesized on Si (100) substrate by thermal oxidation method at different oxidation temperatures 450 oC, 500 oC and 550 oC. The synthesized nanostructures were characterized by FESEM, Uv-Vis and Photoluminescence spectrum. The morphology of the samples was confirmed by FESEM. Meanwhile, the optical properties were obtained from Uv-Vis and photoluminescence (PL) spectrum. Tin oxide nanowires were obtained at oxidation temperatures 500 oC with energy band gaps of 1.21 eV. PL emission spectra results showed that tin oxide nanowires at 500 oC exhibit first maximum peak at 450 nm (2.76 eV), second maximum peak at 500 nm excitation (2.48 eV) and third maximum highest peak at 650 nm excitation (1.91 eV). In this work, we investigate the right oxidation temperature to synthesize tin oxide nanowires. The structural and optical properties of the synthesized tin oxide thin film can be improve by oxidation temperature.
关键词： Photoluminescence,FESEM,nanowires,Tin oxide,thermal oxidation,Uv-Vis,SnO2,nanocrystals
更新于2025-09-09 09:28:46