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Cell Imaging Using Two-Photon Excited CdS Fluorescent Quantum Dots Working within the Biological Window
摘要： In recent years, two-photon excited semiconductor quantum dots (QDs) have been the subject of intense investigation due to their long excitation wavelength which helps to achieve deeper penetration and higher image resolution in optical bioimaging. In this paper, water-soluble CdS QDs were synthesized using a hydrothermal method and applied to human liver hepatocellular carcinoma (HepG2) cells. The first-principles calculation suggested that the S-rich defected structure contributes to a narrower band gap compared to the pristine structure. The resulting fluorescence wavelength was significantly red shifted, which was attributed to the deep defect states emission. The large Stokes shifts (> 200 nm) of the QDs can eliminate the possible cross-talk between the excitation light and the emission light. Two-photon induced red fluorescence emission can avoid overlapping with the autofluorescence emission of biological samples. The uptake and cell viability measurements of the HepG2 cells showed a good biocompatibility and a low toxicity of CdS QDs. Two-photon excited scanning microscopy images revealed that the HepG2 cells incubated with CdS QDs emitted bright red upconversion fluorescence and the fluorescence brightness was 38.2 times of that of the control group. These results support CdS QDs as a good candidate for application in cellular imaging.
关键词： two-photon absorption,CdS quantum dots,deep defect states,HePG2 cells,biological imaging
更新于2025-11-21 11:24:58
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Synthesis, Morphology, Optical and Electrical Properties of Cu <sub/> 1? <i>x</i> </sub> Fe <sub/><i>x</i> </sub> O Nanopowder
摘要： The pure and Fe-doped CuO nanoparticles of the series Cu1?xFexO (x = 0, 0.027, 0.055, 0.097 and 0.125) were synthesized by a simple low temperature sol–gel method. Synthesized samples were characterized by a series of techniques including Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-ray electron spectroscopy (EDX), Diffuse Reflectance Spectroscopy (DRS), Fourier Transform Infrared Spectroscopy (FTIR), Hall Effect Set-up and Current–Voltage (I–V) characteristics. FESEM analysis shows formation of disc type structure increasing in grain size with Fe concentration in CuO. EDX confirmed the incorporation of iron in CuO. FTIR results of pure and Fe doped CuO samples have confirmed the formation of monoclinic CuO. The optical band gap estimated using Diffuse Reflectance Spectroscopy (DRS) shows the increment in the band gap values with Fe substitution. The Hall measurements show predominantly p-type conduction in all the samples and carrier densities decrease with increased Fe substitution. I–V characteristics of pure and Fe doped CuO nanoparticles show rectification behaviour of Schottky diodes.
关键词： Defect States,Hall Effect,Schottky Diode,Cation Vacancies,Fe-Substituted CuO
更新于2025-11-19 16:56:35
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Magnetic metamorphosis of structurally enriched sol-gel derived SnO2 nanoparticles
摘要： Pure SnO2 and aliovalent substituted polycrystalline Sn0.98?xLa0.02ZnxO2 (x = 0.02, 0.04 and 0.06) samples have been synthesized via sol-gel technique. Rietveld re?nement of X-ray di?raction (XRD) patterns con?rm the single phase tetragonal rutile-type (P mnm 42/) crystalline structure for all the synthesized samples. Crystallite size from XRD analysis is found to decrease from 14 nm to 11 nm as x increases from 0 to 0.06 in Sn0.98?xLa0.02ZnxO2 matrix. Transmission Electron Microscopy further reveals the decrease in average crystallite size from 7 nm for pure SnO2 to 5 nm with increase in Zn2+ concentration in system. Morphological study through Field Emission Scanning Electron Microscopy reveals the agglomeration of nanoparticles on increasing the Zn concentration. The room temperature photoluminescence (PL) measurements mark the change in peak intensity centered around 300–450 nm upon La and Zn co-doping into SnO2 lattice. Deconvolution of PL peak unveil the presence of defects/vacancies and local disorders in (La, Zn) co-doped SnO2 matrix. Further, the magnetic properties have been studied using Vibrating Sample Magnetometer, which envisage the room temperature ferromagnetism (RTFM) in nonmagnetic La3+ and Zn2+ ion modi?ed SnO2. The observed RTFM in (La, Zn) co-doped SnO2 is mainly due to oxygen vacancies which is also supported by PL results.
关键词： Rietveld re?nement,RTFM,SnO2 nanoparticles,Defect states
更新于2025-09-23 15:23:52
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Macroscopic effects and microscopic origins of gamma-ray irradiation on In-doped CdZnTe crystal
摘要： The effects of gamma-ray irradiation, exposed to a 60Co source with a dose of 2.7 kGy, on In-doped CdZnTe (CdZnTe:In) crystal were investigated. We combined the “macroscopic” electrical properties of CdZnTe:In sample, evaluated by current–voltage (I–V) measurements at different temperature, with the “microscopic” origins of electrically active defects induced by gamma-irradiation, characterized by thermally stimulated current spectroscopy. It reveals that the bulk resistivity at room temperature have increased from 2.7 × 109 ? cm for the as-grown CdZnTe:In sample to 5.9 × 109 ? cm for the irradiated sample. Since the microscopic origins of these macroscopic effects are linked to the electrically active defects within the material, five main defect states (I, II, III, IV and V) were characterized and identified in the CdZnTe:In crystal. In particular, the introduction of gamma-irradiation altered the trap concentrations of these defect states, such as the rapidly decreasing concentration of region I. Besides, the gamma-ray irradiation caused a further deepening of EDD level (region V) from the value of 0.717 ± 0.004 eV for the as-grown sample to the value of 0.749 ± 0.004 eV for the irradiated sample. The microscopic origin of EDD level was identified with TeCd2+ below the conduction band minimum, which is responsible for the pinning of EF level near the mid-gap, and thus for the observed high-resistivity performance of CdZnTe:In.
关键词： high-resistivity,electrical properties,defect states,gamma-ray irradiation,CdZnTe:In
更新于2025-09-23 15:21:21
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Numerical simulation of multilayer organic light-emitting diodes with hosta??guest emissive layer: the role of defect states
摘要： In this study, a comprehensive model for the numerical simulation of electrical and optical characteristics of multilayer organic light-emitting devices (OLED) is presented. The model consists of three parts: charge carrier transport model, exciton model, and a post-processing part for calculating luminance. The defect states in the organic layers are modeled and are introduced into the equations. For demonstrating the rule of the defect states in such devices, a multilayer OLED is considered consisting of a host–guest emissive layer sandwiched between electron and hole transport layers. The current density and luminance results of the analyzed device are compared with the experimental data. We have found that by considering the defect states, there is good accordance between the simulation results and the experimental data.
关键词： Host–guest emissive layer,Luminance,Current density,OLED,Numerical simulation,Defect states
更新于2025-09-23 15:21:01
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On the role of magnesium in LiF:Mg,Ti thermoluminescent dosimeter
摘要： LiF doped with Mg and Ti is the most widely used thermoluminescent (TL) dosimeter for a large variety of applications. It has been argued that the Mg dopant is the most important defect in the TL process. Besides the common F-centre defects in LiF, optical absorption measurements have suggested the presence of Mg-related absorption bands at 380 nm (3.26 eV), and 310 nm (4.0 eV) when LiF:Mg is exposed to ionizing radiation, whose origin is not yet well understood. This work presents an investigation of the role of defects induced by Mg in LiF through electronic structure calculations. The calculations show that Mg interstitials induce a local lattice distortion characterized by the displacement of two opposite fluorine atoms, adjacent to the magnesium, away from their original sites by an average distance of 0.6 ? each, while the closest Li atoms are displaced by 0.1 ?. This defect introduces electronic states in the band-gap that can trap excess electrons produced during irradiation, thus enhancing the efficiency of the detector. Holes, on the other hand, are created and trapped in orbitals of mainly Mg-3s character. Additionally, the results suggest that irradiation can simultaneously remove a Li atom nearby a Mg interstitial; substitute a Li by a Mg atom or create a Li vacancy plus a Mg substitutional, giving rise to defects within the LiF gap that are more stable thermodynamically than the Mg interstitial itself.
关键词： magnesium dopant,LiF:Mg,Ti,thermoluminescent dosimeter,electronic structure calculations,defect states
更新于2025-09-23 15:21:01
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Modulating Charge-Carrier Dynamics in Mn-Doped All-Inorganic Halide Perovskite Quantum Dots through the Doping-Induced Deep Trap States
摘要： Transition metal ions doping has been demonstrated effective to tune the photoluminescence properties of perovskite quantum dots (QD). However, it would inevitably introduce defects in the lattice. As the Mn concentration increases, the Mn dopant PL quantum yield (PLQY) first increases and then decreases. Herein, the influence of the dopant and the defect states on the photophysics in Mn doped CsPbCl3 QDs was studied by time-resolved spectroscopies, while the energy levels of the possible defect states were analyzed by Density Functional Theory (DFT) calculations. We reveal the formation of deep interstitials defects (Cli) by Mn2+ doping. The depopulation of initial QDs exciton states is a competition between exciton-dopant energy transfer (ET) and defect trapping at an early time-scale (< 100 ps), which determines the final PLQY of the QDs. The present work establishes a robust material optimization guideline for all the emerging applications where high PLQY is essential.
关键词： photoluminescence,energy transfer,Mn-doped,CsPbCl3,DFT calculations,defect states,quantum dots
更新于2025-09-23 15:19:57
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Engineering Point Defect States in Monolayer WSe <sub/>2</sub>
摘要： Defect engineering is a key approach for tailoring the properties of the emerging two-dimensional semiconductors. Here, we report an atomic engineering of the W vacancy in monolayer WSe2 by single potassium atom decoration. The K decoration alters the energy states and reshapes the wave-function such that previously hidden mid-gap states become visible with well-resolved multiplets in scanning tunneling spectroscopy. Their energy levels are in good agreement with first principle calculations. More interestingly, the calculations show that an unpaired electron donated by the K atom can lead to a local magnetic moment, exhibiting an on-off switching by the odd-even number of electron filling. Experimentally the Fermi level is pinned above all defect states due to the graphite substrate, corresponding to an off state. The close agreement between theory and experiment in the off state, on the other hand, suggest a possibility of gate-programmable magnetic moments at the defects.
关键词： mid-gap defect states,spin splitting,defect engineering,local magnetic moment,transition metal dichalcogenides
更新于2025-09-19 17:15:36
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Novel Lewis Base Cyclam Self-Passivation of Perovskites without Anti-Solvent Process for Efficient Light-Emitting Diodes
摘要： Metal halide perovskites have been focused as a candidate applied as a promising luminescent material for next-generation high-quality lighting and high-definition display. However, as perovskite film formed, high density of defects would produce in solution processing inevitably, leading to low exciton recombination efficiency in light-emitting diodes (LEDs). Herein, a facile and novel self-passivation strategy to inhibit defects formation in perovskite film for constructing high performance LEDs is developed. For the first time, we introduce 1,4,8,11-tetraazacyclotetradecane (cyclam) in perovskite precursor solution and it spontaneously passivates defect states of CsPbBr3-based perovskite by coaction between amine and uncoordinated lead ions during spin-coating without anti-solvent process. Furthermore, as a delocalized system, cyclam also possesses chemical properties that facilitate exciton transportation. The proposed passivation strategy boosts the external quantum efficiency (EQE) from 1.25% (control device) to 16.24% (cyclam-passivated device). Further, defects passivation is also conductive to reduce LED degradation paths and improve device stability as the extrapolated lifetime (T50) of LEDs at an initial brightness of 100 cd/m2 is increased from 0.9 h to 127 h. These findings indicate the introduction of cyclam is highly effective to enhance the performance of LEDs, and such strategy in effectively reducing the defects could be also applied in other perovskite-based devices, such as lasers, solar cells, and photodetectors.
关键词： perovskites,self-passivation,light-emitting diodes,defect states,Lewis base cyclam
更新于2025-09-19 17:13:59
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Investigation of Photophysical Properties of Ternary Zn–Ga–S Quantum Dots: Band Gap versus Sub-Band-Gap Excitations and Emissions
摘要： Highly luminescent ternary Zn?Ga?S quantum dots (QDs) were synthesized via a noninjection method by varying Zn/Ga ratios. X-ray diffraction and Raman investigations demonstrate composition-dependent changes with multiple phases including ZnGa2S4, ZnS, and Ga2S3 in all samples. Two distinct excitation pathways were identified from absorption and photoluminescence excitation spectra; among them, one is due to the band-gap transition appearing at around 375 and 395 nm, whereas another one observed nearby 505 nm originates from sub-band-gap defect states. Photoluminescence (PL) spectra of these QDs depict multiple emission noticeable at around 410, 435, 461, and 477 nm arising from crystallographic point defects formed within the band gap. The origin of these defects including zinc interstitials (IZn), zinc vacancies (VZn), sulfur interstitials (IS), sulfur vacancies (VS), and gallium vacancies (VGa) has been discussed in detail by proposing an energy-level diagram. Further, the time-dependent PL decay curve strongly suggests that the tail emission (appear around 477 nm) in these ternary QDs arises due to donor?acceptor pair recombination. This study enables us to understand the PL mechanism in new series of Zn?Ga?S ternary QDs and can be useful for the future utilization of these QDs in photovoltaic and display devices.
关键词： photophysical properties,ternary Zn?Ga?S quantum dots,sub-band-gap defect states,donor?acceptor pair recombination,photoluminescence,band-gap transition
更新于2025-09-16 10:30:52