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Effect of doping mechanism on photogenerated carriers behavior in Cu-doped ZnSe/ZnS/L-Cys core-shell quantum dots
摘要： Cu-doped ZnSe/ZnS/L-Cys core–shell QDs are prepared by both nucleation doping and growth doping in an aqueous synthesis method. Transport of photogenerated free charge carriers (FCCs) in these Cu-doped QDs is probed via a combination of surface photovoltaic (SPV), photoacoustic (PA), and electric-field-induced SPV techniques, supplemented by the UV–VIS absorption spectrum and Raman spectrum. The results confirm that the two doping mechanisms result in different doping locations and microelectronic structures of the Cu-doped QDs. The distinctive microelectronic structure of the QDs prepared by nucleation doping, as compared with those prepared by growth doping, results in a number of favorable SPV characteristics. For example, the QDs prepared by nucleation doping exhibit a higher SPV response intensity at 600 nm because of a higher concentration of photogenerated FCCs. The ratio of the strongest SPV response and the strongest PA signal of the QDs prepared by nucleation doping is up to 2.41 times greater than those of the QDs prepared by growth doping. This is because the greater numbers of photogenerated FCCs in the QDs prepared by nucleation doping generate the PV effect rather than the PA effect that is caused by a nonradiative de-excitation process. The position of the shoulder peak of the SPV response at a long wavelength of the QDs prepared by nucleation doping is significantly red-shifted compared with that of the QDs prepared by growth doping, leading to a broader SPV response range in the visible region. The QDs prepared by nucleation doping have a more obvious donor feature than those prepared by growth doping.
关键词： photogenerated carriers,Cu-doped ZnSe/ZnS/L-Cys,quantum dots,photoacoustic,surface photovoltaic,nucleation doping,growth doping
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - High Power, Ultrafast Yellow Laser using Fourth-Harmonic Generation of Ultrafast Mid-IR Cr <sup>2+</sup> :ZnS Laser in MgO:PPLN Crystal
摘要： The ultrafast optical radiation in the yellow spectral region is of great interest for variety of scientific and technological applications including astronomy, spectroscopy and medicine, with potential to revolutionize eye surgeries through exquisite accuracy [1, 2]. However, it is relatively difficult to access the yellow region, especially when good beam quality, high power and high efficiency are required. Till date, various types of yellow lasers have been reported [3, 4] mostly in CW regime and nanosecond timescales. Here, we report on a compact, high- power, high repetition-rate, ultrafast source of yellow radiation. Using an ultrafast Cr2+:ZnS laser of average power of 4.5 W with spectral width of Δλ=138 nm centered at 2.36 μm, producing output pulses of width ~40 fs at a repetition rate of 80 MHz, and two stage single-pass second harmonic generation (SHG), we have generated ultrafast radiation of power 1 W tunable across 577-589 nm. The schematic of the experimental setup is shown in Fig. 1(a). The single-pass SHG of Cr2+:ZnS laser in a 2 mm long 5% mol doped MgO:PPLN multi-grating crystal (Λ=33.15 - 35.25 μm), giving second harmonic (SH) pulses of 90 fs at 1.18 μm, with a maximum average power of 2.3 W at a single-pass efficiency as high as 65%. Further the 1.18 μm radiation is frequency-doubled in a 1 mm long and 0.5×1 mm2 in aperture, MgO:PPLN crystal (Λ=8.9 -9.45 μm) producing yellow radiation. The acceptance bandwidth (FWHM) and temporal walk-off length (LT) of the second crystal are calculated to be 3 nm and 288 μm, respectively. In order to optimize the focusing condition for maximum fourth harmonic generation (FHG) efficiency, we pumped the crystal at constant power of 1.3 W at 1.18 μm and recorded the fourth harmonic (FH) power as a function of focusing parameter, ξ =L/b, where, L is the length of the crystal and b=2πnw0 2/λ, w0 is the beam waist radius, n is the refractive index of the crystal and λ is the input wavelength.
关键词： Cr2+:ZnS laser,MgO:PPLN crystal,fourth-harmonic generation,ultrafast yellow laser
更新于2025-09-11 14:15:04
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Study of alloyed quantum dots-porphyrazine interaction in solution
摘要： The core-shell quantum dots, namely, CdSxSe1-x/ZnS (QD), and free-base porphyrazine (1) undergoes spontaneous interaction in solution. Steady state fluorescence measurements reveal significant quenching of the photoluminescence of QD in presence of 1. The average value of lifetime of QD (16.10 ns) suffers negligible change in presence of 1 (15.55 ns). The value of bimolecular quenching constant, i.e., kq for QD-1 system (kq = 1.380 × 1011 litre·mol-1·sec-1) determined from time-resolved fluorescence experiment rules out the possibility of diffusion driven process in present work. The mechanism of binding interaction between QD and 1 is established following the evaluation of binding constant value, i.e., K = 12,720 litre·mol-1 for QD-1 system. The results emanating from present work would be very much helpful for employing QD-porphyrazine type system as possible binding unit in energy and/ electron transfer process.
关键词： binding interaction,CdSxSe1-x/ZnS (QD),static quenching,free-base porphyrazine,PL quenching
更新于2025-09-11 14:15:04
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Magneto-fluorescent microbeads for bacteria detection constructed from superparamagnetic Fe <sub/>3</sub> O <sub/>4</sub> nanoparticles and AIS/ZnS quantum dots
摘要： The efficient and sensitive detection of pathogenic microorganisms in aqueous environments such as water used in medical applications, drinking water, and cooling water of industrial plants requires simple and fast methods suitable for multiplexed detection such as flow cytometry (FCM) with optically encoded carrier beads. For this purpose, we combine fluorescent Cd-free Ag-In-S ternary quantum dots (t-QDs) with fluorescence lifetimes (LTs) of several hundred nanoseconds and superparamagnetic Fe3O4 nanoparticles (SPIONs) with mesoporous CaCO3 microbeads to a magneto-fluorescent bead platform that can be surface-functionalized with bioligands such as antibodies. This inorganic bead platform enables immuno-magnetic separation, target enrichment, and target quantification with optical readout. The beads can be detected with steady-state and time-resolved fluorescence microscopy and flow cytometry (FCM). Moreover, they are suited for readout by time gated emission. In the following, the preparation of these magneto-fluorescent CaCO3 beads, their spectroscopic and analytic characterization, and their conjugation with bacteria-specific antibodies are presented as well as proof-of-concept measurements with Legionella pneumophila including cell cultivation and plating experiments for bacteria quantification. Additionally, the possibility to discriminate between the long-lived emission of the LT-encoded capture and carrier CaCO3 beads and the short-lived emission of the dye-stained bacteria with time-resolved fluorescence techniques and single wavelength excitation is demonstrated.
关键词： AIS/ZnS quantum dots,flow cytometry,magneto-fluorescent microbeads,time-resolved fluorescence,superparamagnetic Fe3O4 nanoparticles,bacteria detection
更新于2025-09-11 14:15:04
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Influence of the Cation on the Surface Electronic Band Structure and Magnetic Properties of Mn:ZnS and Mn:CdS Quantum Dot Thin Films
摘要： The effects of doping Mn into ZnS and CdS quantum dots are reported. Scanning tunneling spectroscopy spectra show a reduction in the electronic band gap in both CdS and ZnS upon incorporation of the Mn dopant. Mn:ZnS exhibits a rigid band shift toward higher bias which is reminiscent of a hole doping effect. This rigid band shift in Mn:ZnS is argued, with the help of X-ray photoelectron spectroscopy, to be due to a hole-doping mechanism caused by the favorable formation of Zn vacancies and a reduction in S vacancies compared to undoped ZnS films. In CdS no rigid band shift is observed even though the presence of Cd vacancies can be confirmed by photoemission and magnetic measurements. A strong sp-d hybridization is observed in the Mn:CdS film upon introducing the Mn dopant. d0 ferromagnetism is observed in both undoped ZnS and CdS quantum dot thin films at room temperature. Upon doping of Mn into ZnS the magnetization is reduced suggesting an antiparallel alignment of Mn-Mn or Mn-Zn vacancies nearest neighbors. Density Functional Theory supports the experimental results indicating the nearest neighbor Mn atoms prefer antiparallel alignment of their magnetic moments with preferred ground state of Mn in 3+ oxidation state.
关键词： CdS,Mn doping,quantum dots,magnetic properties,scanning tunneling spectroscopy,electronic band structure,X-ray photoelectron spectroscopy,density functional theory,ZnS
更新于2025-09-11 14:15:04
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Role of hydrazine in the enhanced growth of zinc sulfide thin films using chemical bath deposition for Cu(In,Ga)Se2 solar cell application
摘要： We investigated the hydrazine effect on the physical characteristics of zinc sulfide (ZnS) thin films on both the soda-lime glass substrate and the Cu(In,Ga)Se2 (CIGS) absorber layer as a function of its relative content rc with respect to ammonia as well as the deposition time td in the chemical bath deposition. As the rc varied from 0 to 1.39, all the deposited ZnS films using hydrazine as a secondary complexing agent showed nearly identical characteristics of amorphous structure with the composition of [S/(S + O)] ~ 0.32 and the direct energy bandgap of Eg = 3.54–3.75 eV. However, they exhibited a strong dependence of light transmission on the longer deposition times td (≥70 min), due to the enhancement of the areal density of in-plane grains. By applying the ZnS buffer on top of the CIGS, the heterojunction device showed the best solar cell performance with η = 12.03%, Voc = 0.549 V, Jsc = 32.92 mA/cm2, FF = 66.7% from the ZnS buffer grown at rc = 0.28 and td = 30 min. When compared to only ammonia, the relative hydrazine was found to play a key role in the deposition of ZnS to expedite the in-plane grain growth by 6 times accompanied both with a reduction of in-plane grain size and a denser packing density.
关键词： CIGS solar cell,ZnS thin film,Chemical bath deposition,Hydrazine
更新于2025-09-11 14:15:04
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ZnSe:Cu/ZnS:Cu quantum dots (QDs): synthesis via a simple UV-assisted approach and investigating optical properties
摘要： In this report, first, ZnSe:Cu QDs have been grown by a simple, rapid, and room temperature UV-assisted approach. Then by a one-pot approach, synthesized QDs were shelled by an inorganic ZnS shell. ZnS shell was grown using UV-sensitivity of Na2S2O3. Synthesized QDs were characterized by means of X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDAX), UV–Visible (UV–Vis), and photoluminescence (PL) analysis. ZnS shell growth resulted in increasing green emission of the ZnSe:Cu QDs and PL intensity was increased significantly by ZnS:Cu shell growth. The optimum value of the PL intensity was obtained for ZnSe:Cu(1.5%)/ZnS:Cu(0.05%).
关键词： optical properties,UV-assisted synthesis,ZnS shell,photoluminescence,ZnSe:Cu QDs
更新于2025-09-11 14:15:04
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Photoluminescence Decay of Colloidal Quantum Dots: Reversible Trapping and the Nature of the Relevant Trap States
摘要： Interfaces are crucial factors in shaping the properties of colloidal quantum dots (QDs), in particular the size-dependent optical properties that are a hallmark of these materials. However, the role played by the interfaces associated with QDs on the kinetics of photoluminescence (PL) decay of these nanocrystals is not fully understood even for the most extensively investigated II-VI QDs. In particular, interfaces are a hotbed of trapping sites over which control is essential for efficient performance of QD-based devices, because traps condition PL lifetimes and may be related to PL intermittency. In this work, we analyze the room-temperature PL decay of drop-cast films of CdSe/ZnS QDs varying a number of factors (casting solvent, capping ligands, core/shell interface character). We show how the use of a function that accounts for reversible trapping of photogenerated charge carriers with physically meaningful parameters (time constant, trapping and detrapping rate constants, and average number of traps per QD) can provide valuable information concerning the relevant interfaces, and therefore the nature of the trap states, involved in the recombination of those charge carriers. This approach should be applicable to QDs of a variety of compositions as well as materials beyond inorganic semiconductors.
关键词： photoluminescence decay,trap states,reversible trapping,CdSe/ZnS QDs,colloidal quantum dots
更新于2025-09-11 14:15:04
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Preparation of ZnS-CdS Nanocomposite for Photoelectrochemical Hydrogen Production
摘要： Chalcogenide nanostructures and nanocomposites as semiconductors have attracted intense attentions in various potential applications such as hydrogen production owing their remarkable photoelectrochemical activity. In this study, ZnS-CdS nanocomposite with cubic ZnS and hexagonal CdS was synthesized with a simple wet chemical method. As can be seen from SEM and TEM images, CdS was formed on the outer layer of ZnS NPs. The hydrogen production rate of ZnS-CdS nanocomposite was much higher than that of ZnS NPs, indicating the remarkable enhancement of hydrogen production activity of photocatalyst with the addition of CdS. The hydrogen production rate increased more than 4 times after the deposition of Ru on the surface of ZnS-CdS. In addition, the as-prepared ZnS-CdS nancomposite demonstrated an excellent stability over 50 h.
关键词： CdS,Nanocomposite,ZnS,Hydrogen,Photoelectrochemicallysis
更新于2025-09-11 14:15:04
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Influences of reaction temperature, holding time and S/Zn molar ratio on structure, morphology, optical and electrical properties of ZnS nanoparticles synthesized by hydrothermal method
摘要： ZnS nanoparticles were synthesized by hydrothermal method. The influences of reaction temperature, holding time and S/Zn molar ratio on the structure, morphology, optical and electrical properties of ZnS nanoparticles were studied systematically at the range of 90?°C to 180?°C, 6?h to 15?h and 1:2 to 2.5:1, respectively. The results indicate that the reaction temperature, holding time and S/Zn molar ratio have no influence on phase structure. All the samples belong to zinc blende cubic structure of ZnS. However, the reaction temperature has strong influences on the growth of crystals, optical and electrical properties due to LaMer theory and two-stage growth kinetics. When the reaction temperature increases from 90?°C to 180?°C, the crystallite sizes increase from 7.0?nm to 9.7?nm and the average particle sizes decrease from 21?nm to 14?nm; the emission peaks are red shifted from 445?nm to 460?nm and the emission intensity is increased by 4.4 times; the dielectric constant and dielectric loss decrease from 4.86 to 4.71 and 2.86 × 104 to 2.70 × 104, respectively. While, the holding time has slight influences on the growth of crystals, optical and electrical properties. And the emission band and emission intensity of ZnS nanoparticles can be adjusted by the S/Zn molar ratio. When the S/Zn molar ratio is less than 1:1 or equal to 1:1, the emission bands range from 400?nm to 600?nm centered at ~ 450?nm. When the S/Zn molar ratio is greater than 1:1, the emission bands range from 400?nm to 700?nm centered at ~ 540?nm.
关键词： Holding time,Optical properties,Reaction temperature,Hydrothermal method,S/Zn molar ratio,ZnS nanoparticles,Electrical properties
更新于2025-09-10 09:29:36