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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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Effect of Temperature of Electron Beam Evaporated CdSe Thin Films
摘要： CdSe thin films were deposited on a glass substrate by using electron beam evaporation technique. The as deposited films were annealed from 100oC to 300°C with an increment of 100°C. Morphological, structural and optical characterization of the films was carried out by using scanning electron microscope (SEM), X-ray diffraction (XRD), ultraviolet-visible (UV-Vis) spectroscopy; and Fourier transform infrared spectroscopy. The X-ray diffraction pattern that the film has a cubic phase with preferred orientation (100), the grain size was found to be in the range of 29-46 nm. SEM results reveal that film grains are polycrystalline in nature covered the whole surface of the substrate.
关键词： FTIR,CdSe thinfilm,Scanning electron microscope,X-ray diffraction (XRD)
更新于2025-09-10 09:29:36
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Formation energies of CdSe wurtzoid and diamondoid clusters formed from Cd and Se atomic clusters
摘要： Cadmium Selenide thermodynamic formation energies at the molecular and nanoscale range are investigated using density functional theory. The investigation is performed using wurtzoid and diamondoid clusters that represent the wurtzite and zincblende structures at the molecular and nanoscale size range for a cluster number of atoms n ≤ 26. Cd and Se atomic clusters are optimized and used to provide component atomic cluster energies. Although both Cd and Se clusters at the nanoscale have di?erent phases than bulk, the results show that Gibbs free energy, enthalpy, and entropy of formation of CdSe are close to their experimental bulk energies of formation within errors of experimental measurements. CdSe wurtzoids generally have higher absolute (more negative) Gibbs free energy of formation than CdSe diamondoids indicating more stable wurtzoid molecules which is also the case at bulk. The absolute Gibbs free energy of wurtzoids is also higher than experimental value (more negative) because of surface e?ects at the nanoscale. Enthalpy of formation indicates an exothermic reaction of Cd and Se clusters as is the case at bulk. The entropy of formation of all clusters is size-sensitive and converges towards bulk experimental measurements. Both wurtzoids and diamondoids members contain Cd13Se13 cluster which is the most investigated magic CdSe cluster.
关键词： Density functional theory,CdSe,Cluster
更新于2025-09-10 09:29:36
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Optical and Structural Characteristics of CdSe/PMMA Nanocomposites
摘要： Nanocomposites of polymethylmethacrylate (PMMA) and CdSe were fabricated by a casting technique. The result showed that CdSe@PMMA can be used in white and green light emitting devices. 0.01CdSe@PMMA exhibits monochromatic green color emission with the highest fluorescent quantum yield and lowest optical band gap value, while CdSe@PMMA with other ratios shows a multicolor emission. The band-edge emits in the vicinity of 280 – 296 nm but a more stable intensive green color emission at 553 nm is found for 0.01CdSe@PMMA. The change in Eg (4.18 to 4.4) eV values is due to the interaction between the PMMA polymer and CdSe.
关键词： nanocomposites,optical properties,PMMA,light emitting devices,CdSe
更新于2025-09-10 09:29:36
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Construction of Z-scheme MoSe2/CdSe Hollow Nanostructure with Enhanced Full Spectrum Photocatalytic Activity
摘要： For better use of solar energy, the development of full-spectrum photocatalysts has attracted most attentions. In this research, uniform hollow MoSe2/CdSe nanospheres (250 nm) were prepared by one-pot solvothermal strategy. It is the first time to synthesize hollow MoSe2 based nanostructure without any template/surfactant assistance. By varying reaction time, the formation mechanism was investigated, illuminating that the novel hollow structure is derived from the Kirkendall Effect. Both experimental and density functional theory (DFT) calculations reveal the Z-scheme mechanism of the charge transfer in the heterostructure. The hollow MoSe2/CdSe nanospheres (MC2) possess the remarkable photocatalytic activity in degradation of Cr(VI) (125 mg g-1, simulated sunlight), owing to the high harvest of full spectrum, porous hollow structure and effective charge separation/transfer. Furthermore, the photocatalytic process was further studied in detail, showing that the Langmuir single-layer adsorption behavior, low pH value condition, and thermal effect also benefit to the high photoreduction performance. Benefiting from the Z-scheme mechanism, the high redox activity make sure the water splitting capacity of MC2 (7120.0 and 348.0 μmol·h-1·g-1 of H2 and O2 evolution) under simulated sunlight irradiation and its AQY for H2 evolution at 670 nm reaches up to 27.2% (50 mg MC2).
关键词： Z-scheme,Water splitting,Cr(VI) photoreduction,Hollow MoSe2/CdSe nanospheres,Full Spectrum photocatalysis
更新于2025-09-10 09:29:36
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Energy Transfer from CdSe/ZnS Nanocrystals to Tetraphenyl Porphyrin
摘要： CdSe/ZnS nanocrystals (NCs) and Tetraphenyl Porphyrin (TPP) are mixed uniformly to prepare CdSe/ZnS NCs/TPP complex. TPP can quench the fluorescent signal of CdSe/ZnS NCs. UV-Vis absorption spectra and fluorescence spectra are employed to analysis the energy transfer. The mechanism of energy transfer is the F?rster resonance energy transfer from CdSe/ZnS to TPP.
关键词： Tetraphenyl Porphyrin,energy transfer,CdSe/ZnS nanocrystals,F?rster resonance energy transfer
更新于2025-09-10 09:29:36
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The Remote Light Emission Modulated by Local Surface Plasmon Resonance for the CdSe NW-Au NP Hybrid Structure
摘要： CdSe nanowire (NW)–Au nanoparticle (NP) compounds are synthesized successfully using the method of physical vapor deposition, and the modulated remote emission is realized in the hybrid structure with strong metal–semiconductor coupling. The well-crystallized, uniform morphology, smooth surface CdSe NW is attached with an Au NP on the terminal, which forms the integration structure with direct plasmon–exciton coupling of semiconductor–metal hybrid system. When the CdSe terminal or Au NP terminal of the hybrid structure is excited by the laser with wavelength of 633 nm, the remote light emission at another terminal is greatly modulated. To reveal the physical mechanism of energy conviction between plasmon and exciton, finite-difference time-domain simulations are performed for the CdSe NW–Au NP hybrid structures. The calculated results confirm that the modulation of remote light emission is attributed to the competing of the quench of photoluminescence and the electric field enhancement of local surface plasmon resonance. These works can provide deeper understanding of physical mechanism of plasmon and exciton coupling, and open up new application for the remote light sensing and detection.
关键词： localized electromagnetic field enhancement,remote light emission,CdSe NW,Au NP,photoluminescence
更新于2025-09-10 09:29:36
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The preparation and photocatalytic performance research of CdSe and wool ball-like GO/CdSe microspheres
摘要： Different morphologies of CdSe and GO (graphene oxide)/CdSe microspheres like wool ball and walnut shape have been made through hydrothermal method using CTAB as surfactant. X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), X-ray energy dispersive spectrometer (EDS), scanning electron microscope (SEM), Raman spectra, and UVevis absorption spectrum, were used to intensively investigate the structures, morphologies, chemical compositions and optical properties of CdSe and GO/CdSe microspheres. The results of XRD revealed that GO/CdSe microspheres have lead-zinc mineral structure. The results of XRD, EDS, XPS and Raman spectra showed that GO/CdSe microspheres were grown on GO sheets. Also UVevis absorption spectrum indicated that GO/CdSe microspheres enhanced absorbance in UV light region and visible light region. Through comparative experiments, the results showed that pH ? 4 is the optimal pH value for degrading Rhodamine B (RhB) solution. To study the photocatalytic performance of GO/CdSe microspheres, we catalyzed the degradation of RhB aqueous solution irradiated by visible light. The photocatalytic results showed that the wool ball-like GO/CdSe microspheres exhibited better photocatalytic activity than rough CdSe.
关键词： GO/CdSe microspheres,Hydrothermal method,Morphologies,GO,Photocatalytic activity
更新于2025-09-10 09:29:36
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Barrier Height Inhomogeneity in Mixed-dimensional Graphene/Single CdSe Nanobelt Schottky Junctions
摘要： Mixed-dimensional graphene/single CdSe nanobelt (NB) Schottky junctions are fabricated and the influence of Schottky barrier inhomogeneity on the electrical transport mechanism is investigated. The ideality factor increases and the zero-bias Schottky barrier height (SBH) decreases monotonically, as temperature decreases from 300 to 80 K. The temperature-dependent electrical transport characteristics can be explained by the SBH inhomogeneity, which may arise from the inevitable grain boundaries, topographic corrugation and charge puddles in the as-fabricated graphene, surface states and nonuniform dopant concentration in CdSe NB. We use a spatial potential fluctuation model to analyze the conduction mechanism, where the SBH with a Gaussian distribution is assumed. The standard deviations of SBH distribution are up to 13.06% and 14.09% of the mean value of zero-bias SBH in 80–140 K and 140–300 K, respectively, implying strong SBH inhomogeneity in typical graphene/CdSe NB junctions. This work reveals fundamental physical properties in the graphene/CdSe NB interfaces, and might contribute to the future design and implementation of graphene based nano-devices.
关键词： Graphene,inhomogeneity,CdSe Nanobelt,Schottky junction
更新于2025-09-10 09:29:36
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Disentangling the Electron and Hole Dynamics in Janus CdSe/PbSe Nanocrystals through Variable Pump Transient Absorption Spectroscopy
摘要： CdSe/PbSe Janus hetero-nanocrystals (HNCs) represent an interesting system where structurally immiscible CdSe and PbSe co-exist in a single structure with intermixed electronic states. Here, we have investigated the carrier dynamics in Janus CdSe/PbSe HNCs through ultrafast transient absorption spectroscopy by selectively exciting either the CdSe or the PbSe domains. Upon excitation of the CdSe domain sub-picosecond hole transfer to the hybrid interfacial PbSe states were identified. On the other hand, the transfer of hot electron from PbSe to CdSe was evident upon creation of hot electrons in PbSe domain without exciting the CdSe domain. The photo-excited hot hole also gets transferred to the hybrid interfacial states in sub-ps time (~1ps) bleaching the corresponding transition. The decay of the localized hole was found to be much slower compared to the electron which can be beneficial for carrier extraction and multiexciton generation. The finding of hot electron transfer in a single structure and slow decay of holes can thus prove to be advantageous for future design of photovoltaic devices.
关键词： carrier dynamics,ultrafast transient absorption spectroscopy,CdSe/PbSe Janus hetero-nanocrystals,photovoltaic devices,hot electron transfer
更新于2025-09-10 09:29:36