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Morphological and optoelectronic investigations of CsPbBr3 nanocrystals chelating diphenylammonium halide ligands via low temperature synthesis
摘要： In this study, the low temperature method was adopted to synthesize all-inorganic cesium lead bromide CsPbBr3 nanocrystals (NCs) as the active layer in light-emitting devices. In order to improve film-forming and optoelectronic properties of CsPbBr3 NCs, a surface ligand diphenylammonium bromide (DPABr) was added from 0 to 0.15 mole fraction in proportion to the amount of oleylamine. The experimental results showed that introducing 0.1 mole fraction of DPABr in CsPbBr3 NCs brought the best performance. The SEM and AFM results revealed that smooth and pinhole-free films of CsPbBr3 NCs were formed by introducing DPABr with a low surface roughness of 4.6 nm. The introduced bromide ions can passivate the surface vacancies of CsPbBr3 NCs and improve photoluminescence quantum yield (PLQY) from 38% to 72% compared with the pristine CsPbBr3 NCs. Moreover, shorter and π electron-rich phenyl groups help to increase carrier injection into nanocrystalline core, preventing carriers from being hindered by oleic acid and oleylamine with longer alkyl chains. Therefore, the conductivity of the resulting CsPbBr3 NCs was augmented. The maximum brightness and current efficiency of the optimized device based on CsPbBr3 NCs with 0.1 mole fraction of DPABr were enhanced 2.3- and 3.3-fold, respectively, relative to the pristine one.
关键词： perovskite nanocrystals,low temperature method,photoluminescence quantum yield,surface passivation,diphenylammonium bromide
更新于2025-09-23 15:21:01
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Highly luminescent and stable CH3NH3PbBr3 quantum dots with 91.7% photoluminescence quantum yield: Role of guanidinium bromide dopants
摘要： Although perovskite quantum dots (PQDs) have received considerable attention, defects in PQDs can significantly degrade the properties and device performance. In this study, we report on an effective strategy for synthesizing highly luminescent CH3NH3PbBr3 quantum dots (QDs) by a simple doping. To remove such defects, guanidinium bromide (GuBr) was doped into the CH3NH3PbBr3 QDs synthesized by the ligand-assisted reprecipitation technique. From XRD and TEM studies, the doping of GuBr into the QD lattices was verified. In addition, the surfaces of PQDs with and without GuBr dopants were analyzed by XPS to trace the metallic Pb acting as a major recombination center. The GuBr doping resulted in the size uniformity of QDs and effectively eliminated defects and metallic Pb, which enhanced the photoluminescence quantum yield (PLQY) through the inhibition of the non-radiative recombination pathway. Furthermore, the recombination dynamics in the QDs were examined by using time-resolved photoluminescence and fluorescence lifetime imaging to verify the role of GuBr dopants. By optimizing the amount of GuBr doping, the CH3NH3PbBr3 QDs with strong green emission achieved a maximum PLQY of 91.7%.
关键词： Photoluminescence quantum yield,Fluorescence lifetime imaging,CH3NH3PbBr3 quantum dots,Guanidinium bromide,Recombination centers
更新于2025-09-23 15:19:57
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Zinc Oxo Clusters Improve the Optoelectronic Properties on Indium Phosphide Quantum Dots
摘要： This study explored the effect of zinc precursors on the optical properties of InP quantum dots (QDs) by controlling the reactivity of zinc carboxylates via a simple thermal treatment. The formation of zinc oxo clusters, Zn4O(oleate)6 and Zn7O2(oleate)10, during the thermal decomposition of zinc oleate was confirmed by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. By using the zinc oxo clusters as reaction precursors, high-quality InP QDs with high photoluminescence quantum yield (PLQY) and narrow full width at half maximum (FWHM) were synthesized. (Green QDs: PLQY=95%, FWHM=37 nm. Red QDs: PLQY=84%, FWHM=40 nm) The analysis results showed that the improved optoelectronic properties were achieved by two important functions of the zinc oxo clusters: 1) suppressing the rapid depletion of the highly reactive phosphorus source and inducing size uniformity of the In(Zn)P core, and 2) facilitating the formation of an oxidized buffer layer, which effectively controls defects. Likewise, the use of reactivity-controlled species is an effective strategy for the synthesis of well-designed QDs.
关键词： full width at half maximum,InP quantum dots,optoelectronic properties,photoluminescence quantum yield,zinc oxo clusters
更新于2025-09-23 15:19:57
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Monolayer single crystal two-dimensional quantum dots via ultrathin cutting and exfoliating; è??è?????????????￥?|?????¤?????±????????o???′é???-???1;
摘要： Two-dimensional (2D) atomically thin quantum dots (QDs) possess extraordinary electrical and optical properties. However, fabricating high quality 2D QDs via a universal and reliable technique remains a challenge. Here, we report a simple strategy to prepare high quality, monolayer single crystal 2D QDs via ultrathin cutting 2D bulk single crystals by ultramicrotome, followed by an exfoliation process. The as-prepared 2D QDs have pristine surface, high quality, high monolayer yield and high photoluminescence quantum yield (the highest photoluminescence quantum yield of WS2 is 18%), which can be used as promising, low toxic, biocompatible, and good cell-permeability fluorescent labeling agents for in vitro imaging.
关键词： photoluminescence quantum yield,ultra-thin cutting,single crystal,two-dimension,quantum dots
更新于2025-09-23 15:19:57
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Ammonium acetate passivated CsPbI3 perovskite nanocrystals for efficient red light-emitting diodes
摘要： Lead halide perovskite nanocrystals (PNCs) have very recently emerged as promising emitters for their superior optoelectronic properties. However, the defects in perovskite itself make it susceptible to the external environment and internal ion migration, resulting in low photoluminescence quantum yield (PLQY) and poor device efficiency. Herein, we developed a method to reduce the surface defects of PNCs by introducing ammonium acetate in the synthesis of CsPbI3 PNCs. The addition of ammonium acetate can effectively eliminate undesired surface metallic lead cations and dangling bonds, resulting in an enhanced PLQY and stability. The passivated PNCs have an overall up-shift energy level, demonstrating better hole injection efficiency. As a result, the red light-emitting diodes (LEDs) fabricated with the passivated CsPbI3 PNCs achieved an optimal EQE of 10.6% and a maximum brightness of 981 cd/m2, which are 3.1 and 2.4 times that of unpassivated PNCs based devices, respectively.
关键词： CsPbI3 nanocrystals,ammonium acetate,defect passivation,photoluminescence quantum yield,light-emitting diodes
更新于2025-09-23 15:19:57
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High-efficiency perovskite nanocrystal light-emitting diodes <i>via</i> decorating NiO <sub/>x</sub> on the nanocrystal surface
摘要： Nickel oxides exhibit a great potential as hole transport layers for the fabrication of efficient perovskite light-emitting diodes (LEDs) due to their high carrier mobility and good energy band matching with perovskite nanocrystals. In this work, nickel oxides were directly decorated on the CsPbBr3 nanocrystal surface through adsorption and a sequential oxidation treatment. The resulting sample shows a high photoluminescence quantum-yield of 82%. The LED using CsPbBr3 nanocrystals with nickel oxides achieves a high external quantum efficiency (EQE) of up to 16.8% with a low turn-on voltage of 2.8 V, which is much superior to that of the counterpart LED based on pristine CsPbBr3 nanocrystals (EQE = 0.7%, turn-on voltage = 5.6 V). The excellent performance of the nickel oxide decorated CsPbBr3 nanocrystal device could be attributed to the better energy level matching between the decorated nanocrystals and the transport layers of the device and more balanced charge carrier injection. Furthermore, the operational lifetime of the nickel oxide decorated CsPbBr3 nanocrystal device is 40 times longer than that of the pristine CsPbBr3 nanocrystal device.
关键词： perovskite nanocrystals,photoluminescence quantum-yield,light-emitting diodes,external quantum efficiency,nickel oxides
更新于2025-09-19 17:13:59
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Synthesis of Colloidal Blue-Emitting InP/ZnS Core/Shell Quantum Dots with the Assistance of Copper Cations
摘要： Colloidal InP quantum dots (QDs) have been considered as one of the most promising candidates for the applications in display and bio-label due to intrinsic toxicity-free and high photoluminescence. On account of the uncontrollable nucleation and growth for the synthesis of InP, it remains a challenge to obtain high-quality blue-emitting InP QDs with uniform size distribution. Herein, we employ a novel synthetic approach for producing blue-emitting InP/ZnS core/shell QDs with the assistance of copper cations. The studies reveal that the copper ions could combine with phosphorus precursor to form hexagonal Cu3-xP nanocrystals, which competed with the nucleation process of InP QDs, resulting in the smaller sized InP QDs with blue photoluminescence emission. After the passivation of InP QDs with ZnS shell, the synthesized InP/ZnS core/shell QDs present bright blue emission (~425 nm) with photoluminescence quantum yield (PLQY) of ~25%, which is the shortest wavelength emission for InP QDs till now. This research provides a new way to synthesize ultra-small semiconductor nanocrystals.
关键词： InP/ZnS core/shell,blue-emitting,Colloidal InP quantum dots,photoluminescence quantum yield,copper cations
更新于2025-09-12 10:27:22
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Efficient Quasi-Two-Dimensional Perovskite Light-Emitting Diodes with Improved Multiple Quantum Well Structure
摘要： Quasi-two-dimensional (quasi-2D) perovskites with a multiple quantum well structure can enhance the exciton binding energy and controllable quantum con?ne e?ect, which are attractive materials for e?cient perovskite light-emitting diodes (PeLEDs). However, the multiphase mixtures contained in these materials would cause nonradiative recombination at the perovskite ?lm surface. Here, a facile solution surface treatment is adopted to improve the multiple quantum well structure of the quasi-2D perovskite emitting layer, which can reduce the in?uence of defectinduced nonradiative recombination and the electric-?eld-induced dissociation of excitons for the PeLEDs. The improved multiple quantum well structure is veri?ed by UV absorption spectra and temperature-dependent photoluminescence spectra measurements. The photoluminescence quantum yield of the quasi-2D perovskite ?lm with surface treatment has been approximately increased by 200%. Meanwhile, the electroluminescence device achieves a current e?ciency of 45.9 cd/A.
关键词： electroluminescence,quasi-two-dimensional perovskite light-emitting diodes,surface treatment,multiple quantum well structure,photoluminescence quantum yield
更新于2025-09-12 10:27:22
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Optical properties of chiral single-walled carbon nanotubes thin films
摘要： This work contains experimental results of optical properties for thin films containing Single-Walled Carbon Nanotubes. Thin films concerning 0.5, 1 and 2 mg of low dimension chiral (10,6) Single-Walled Carbon Nanotubes dispersed in low concentration aqueous sodium dodecyl sulfate solution (2 mL) were successfully fabricated by spin-coating technique on transparent substrates at ambient atmosphere. Optical properties of these thin films were examined using Transmission, Raman and Photoluminescence Spectroscopies. We find that investigated chiral Single-Walled Carbon Nanotubes show transmission and emission bands not only in infrared range but also ultraviolet and visible range.
关键词： Absorbance,Single-walled carbon nanotubes,Raman spectra,Photoluminescence,Decay time of photoluminescence,Quantum yield
更新于2025-09-11 14:15:04
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Ultrafast Dynamics and Ultrasensitive Single-Particle Intermittency in Small-Sized Toxic Metal Free InP Based Core/Alloy-shell/Shell Quantum Dots: Excitation Wavelength Dependency Towards Variation of PLQY
摘要： Observation of strong deviation of photoluminescence excitation curve from absorption curve specially at lower wavelength range, below 450 nm in case of small sized toxic metal free InP based core-alloy-shell quantum dots hints towards interesting exciton dynamics. PL quantum yield (PLQY) has been observed to be dependent on the excitation wavelength. Monitoring the bleach dynamics employing femtosecond ultrafast pump-probe technique it could be shown that the rise-time increases with decrease in pump excitation wavelength from 100 fs for 550 nm excitation to 220 fs for 430 nm pump/excitation. Therefore exciton cooling takes longer time for lower wavelength excitation and thus the exciton becomes more prone to get trapped. About two fold enhancement in magnitude of normalized bleach signal at the band edge (~0.1 (for 430nm excitation) to ~0.2 (for 550nm excitation)) following exciton relaxation has been observed. Thus, in comparison to lower wavelength excitation, for near band-edge pump/excitation there is higher probability of radiative exciton recombination, therefore increasing PLQY. Hot exciton trapping dynamics has been noted to be occurring at a timescale ~750 fs. From ultra-sensitive single particle measurement, magnitude of power-law exponent for both ON and OFF events remain similar to each other and the magnitude remains unaltered for different excitation wavelengths, (405 nm to 568 nm). As long as 100 s ON event could be observed making this InP based non-toxic QD quite suitable for single particle tracking etc. Interestingly, ON event truncation time has been found to increase from 6s to 16s and OFF event truncation time has been found to decrease from 11s to 5.5s, thereby exciton detrapping rate / trapping rate increases from 0.5 to nearly 3 on going from 405 nm to 568 nm excitation. Thus, as the trapping gets suppressed and detrapping gets enhanced, PLQY gets enhanced. The extent of relative decrease of PLQY value with increase in excitation energy above band-edge has been observed to be much more pronounced in CdSe based CAS QD than InP based CAS QD.
关键词： ultrafast dynamics,photoluminescence quantum yield,excitation wavelength dependency,InP based quantum dots,single-particle intermittency
更新于2025-09-11 14:15:04