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Phonon-Driven Energy Relaxation in PbS/CdS and PbSe/CdSe Core/Shell Quantum Dots
摘要： We study the impact of the chemical composition on phonon-mediated exciton relaxation in the core/shell quantum dots (QDs), with 1-nm core made of PbX and the monolayer shell made of CdX, where X=S and Se. For this, time-domain non-adiabatic dynamics (NAMD) based on Density Functional Theory (DFT) and Surface Hopping techniques are applied. Simulations reveal twice faster energy relaxation in PbS/CdS than PbSe/CdSe due to dominant couplings to higher-energy optical phonons in structures with sulfur anions. For both QDs, the long-living intermediate states associated with the core-shell interface govern the dynamics. Therefore, a simple exponential model is not appropriate, and the four-state irreversible kinetic model is suggested instead, predicting 0.9 ps and 0.5 ps relaxation rates in PbSe/CdSe and PbS/CdS QDs, respectively. Thus, 2-nm PdSe/CdSe QDs with a single monolayer shell exhibit the phonon-mediated relaxation time sufficient for carrier multiplications to outpace energy dissipation and benefit the solar conversion efficiency.
关键词： Density Functional Theory,phonon-driven energy relaxation,PbSe/CdSe,PbS/CdS,core/shell quantum dots,Surface Hopping techniques,non-adiabatic dynamics
更新于2025-09-23 15:21:01
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A discrete core-shell-like micro-light-emitting diode array grown on sapphire nano-membranes
摘要： A discrete core-shell-like micro-light-emitting diode (micro-LED) array was grown on a 100 nm-thick sapphire nano-membrane array without harmful plasma etching for chip singulation. Due to proper design for the sapphire nano-membrane array, an array of multi-faceted micro-LEDs with size of 4 μm × 16 μm was grown. threading dislocation density in the micro-LeD formed on sapphire nano-membrane was reduced by 59.6% due to the sapphire nano-membranes, which serve as compliant substrates, compared to GaN formed on a planar substrate. Enhancements in internal quantum efficiency by 44% and 3.3 times higher photoluminescence intensity were also observed from it. Cathodoluminescence emission at 435 nm was measured from c-plane multiple quantum wells (MQWs), whereas negligible emissions were detected from semi-polar sidewall facets. A core-shell-like MQWs were formed on all facets, hopefully lowering concentration of non-radiative surface recombination centers and reducing leakage current paths. This study provides an attractive platform for micro-LEDs by using sapphire nano-membrane.
关键词： internal quantum efficiency,photoluminescence,threading dislocation density,micro-LED,sapphire nano-membrane,core-shell-like,cathodoluminescence
更新于2025-09-23 15:21:01
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Organic Printed Core-Shell Heterostructure Arrays: A Universal Approach to All-Color Laser Display Panels
摘要： We demonstrate a universal approach for realizing dual-wavelength lasing in organic core-shell structured microlaser arrays, which show great promise in serving as all-color laser display panels. By alternately printing hydrophilic and hydrophobic laser dye solutions on preprocessed substrates, we successfully obtained precisely patterned core-shell heterostructure arrays. The spatially-separated core and shell independently function as optical resonators to support dual-wavelength tunable microlasers in each heterostructure. Such a general method enables to flexibly control the lasing wavelength of the core-shell microlasers across a wide spectral range by systematically designing the gain media. Using as-prepared microlaser arrays as display panels, we achieved full-color laser displays, representing an achievable color gamut much larger than that of standard RGB space. These results may provide new insights for design concepts and device construction for novel optoelectronic applications.
关键词： organic heterostructure,laser display,dual-wavelength laser,core-shell structure,laser array
更新于2025-09-23 15:21:01
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Tunable thermo-piezo-plasmonic effect on core/shell nanoparticles under laser irradiation and external electric field
摘要： This work is focused on the characterization of the opto-heating generation in thermo-piezo-plasmonic solutions of gold-PbZrTiO3 (PZT) core/shell nanoparticles. Core/shell nanoparticles have been prepared by the laser ablation in liquid method. Linear and nonlinear optical properties of proposed nanoparticles were studied by optical spectroscopy and the Z-scan technique under external voltage to investigate the piezo-photonic effect. Furthermore, the linear optical properties of these nanostructures were calculated vie dipole approximation method with different core size and different shell thickness of samples immersed in water and poly-vinyl-pyrrolidone. In addition, thermo-plasmonic effects of samples are investigated theoretically and experimentally by the finite element method of COMSOL multiphysics V5.4 and infrared camera under laser irradiation and external electric field. The results revealed a clear tunable and adjustable linear and nonlinear behavior and thermo-piezo-plasmonic properties under external effects. The temperature elevation is ranging of ?T = 3.7–14.1 °C under different external effects. Accordingly, these results encourage to uses proposed samples for the cancer treatment and the different biomedical applications.
关键词： Nonlinear refractive index,External electric field,Core/shell NPs,Laser irradiation,Thermoplasmonic,Piezoelectric,Z-scan technique,Schottky barrier
更新于2025-09-23 15:21:01
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A Selfa??Powered Higha??Performance UV Photodetector Based on Corea??Shell GaN/MoO <sub/>3a??</sub><i> <sub/>x</sub></i> Nanorod Array Heterojunction
摘要： Self-powered UV photodetectors are highly desirable for applications in space communications and environmental monitoring. However, most self-powered UV photodetectors exhibit unimpressive performance in weak signal detection. Herein, a self-powered UV photodetector based on the core–shell GaN/MoO3–x nanorod array (NRA) heterojunction system is demonstrated. Homogeneous MoO3–x layers are deposited on GaN NRAs by a simple one-step physical vapor deposition method. The photodetector device shows an ultrahigh specific detectivity of 2.7 × 1015 Jones at 355 nm without any power supply. Further analyses reveal a responsivity of 160 A W?1 and a high UV–vis rejection ratio (R355 nm/R400 nm) of 2.0 × 104 under zero bias. The self-powered device also has a fast response speed with a rise/fall time of 73/90 μs. As a result, the self-powered photodetector, featuring ultrahigh detectivity and responsivity along with fast response, exhibits great potential for applications in next-generation UV detection. The core–shell NRA structure heterojunction design provides a valuable direction for realizing nanoscale self-powered UV photodetectors.
关键词： core–shell nanorod arrays,UV photodetectors,ultrahigh detectivity,self-powered devices
更新于2025-09-23 15:21:01
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Ultrathin TiO2-coated SiO2 nanoparticles as light scattering centers for quantum dot-sensitized solar cells
摘要： SiO2/TiO2 core/shell nanoparticles (ST-NPs) with an ultrathin and conformal TiO2 shell were fabricated via atomic layer deposition (ALD) technique with a specially-designed rotary reactor. We successfully employed the ST-NPs as light scattering centers in a mesoporous TiO2 photoanode in quantum dot (QD)-sensitized solar cells (QDSSCs). ST-NPs enhanced the light scattering in the TiO2 photoanode without deterioration of QD loading behavior. Consequently, visible light absorbance was improved in the PbS QDs-sensitized TiO2 photoanode, and thus the photocurrent density increased from 14 to 17 mA/cm2. Detailed electron microscopy was utilized to reveal the uniqueness of the ultrathin TiO2 shell in ST-NPs, and in-depth electrochemical impedance spectroscopy divulged the increase in photogenerated carrier lifetime and improved recombination resistance for the QDSSC with ST-NPs.
关键词： Core-shell,SiO2,Atomic layer deposition,QDSSCs,Light scattering
更新于2025-09-23 15:21:01
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Structural properties of silicon–germanium and germanium–silicon core–shell nanowires
摘要： Core–shell nanowires made of Si and Ge can be grown experimentally with excellent control for different sizes of both core and shell. We have studied the structural properties of Si/Ge and Ge/Si core–shell nanowires aligned along the [1 1 0] direction, with diameters up to 10.2 nm and varying core to shell ratios, using linear scaling density functional theory. We show that Vegard’s law, which is often used to predict the axial lattice constant, can lead to an error of up to 1%, underlining the need for a detailed ab initio atomistic treatment of the nanowire structure. We analyse the character of the intrinsic strain distribution and show that, regardless of the composition or bond direction, the Si core or shell always expands. In contrast, the strain patterns in the Ge shell or core are highly sensitive to the location, composition and bond direction. The highest strains are found at heterojunction interfaces and the surfaces of the nanowires. This detailed understanding of the atomistic structure and strain paves the way for studies of the electronic properties of core–shell nanowires and investigations of doping and structure defects.
关键词： Vegard’s law,nanowire,linear scaling density functional theory,core–shell
更新于2025-09-23 15:21:01
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Polarizability of Radially Inhomogeneous Subwavelength Spheres
摘要： In this work the polarizability of a subwavelength core-shell sphere is considered, where the shell exhibits a radially inhomogeneous permittivity profile. The mathematical treatment of the electrostatic polarizability is formulated in terms of the scattering potentials and the corresponding scattering amplitudes. As a result, a generalized expression of the polarizability is presented to be dependent of the radial inhomogeneity function. The extracted general model is applied for two particular cases, i.e., a power-law profile and a new class of permittivity profiles that exhibit exponential radial dependence. The proposed analysis quantifies in a simple manner the inhomogeneity effects, allowing the direct implementation of naturally or artificially occurring permittivity inhomogeneities for a wide range of applications within and beyond the metamaterial paradigm. Specifically, a special case of symmetric-antisymmetric resonant plasmonic degeneracy is identified and shown for the case of a core-shell sphere with a power-law permittivity profile. This degeneracy could be used for the experimental identification of inhomogeneity-induced effects or for applications where a strong coupling resonant regime is required. Furthermore, the described analysis opens avenues towards the phenomenological and first-principles modeling of the electrodynamic scattering effects for graded-index plasmonic particles at the nanoscale. Finally, such a description can be readily used either for the benchmarking of novel computational methods incorporating inhomogeneous materials or for inverse scattering purposes.
关键词： inverse scattering,subwavelength,core-shell sphere,scattering potentials,metamaterial,exponential radial dependence,polarizability,scattering amplitudes,plasmonic degeneracy,radially inhomogeneous permittivity,power-law profile
更新于2025-09-23 15:21:01
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Synthesis of hollow core-shell CdS@TiO2/Ni2P photocatalyst for enhancing hydrogen evolution and degradation of MB
摘要： During the photocatalytic production of hydrogen gas, close interface with a catalyst is very important. We designed a noble-metal-free photocatalytic system that is spatially separated to produce hydrogen by high frequency visible light. We used a new type of a catalyst consisting of hollow core-shell CdS@TiO2/Ni2P structures prepared using sacrificial template method. Photocatalytic decomposition of water was tested using this catalyst. Hydrogen production yield using 420 nm light was 14.80 mmol/g after 2.5 h and using Xe lamp with AM1.5G filter was 34.78 mmol/g after 2.5 h. Hollow core shell CdS@TiO2/Ni2P particles were more stable than hollow core shell CdS@TiO2/Pt structures because TiO2 protected CdS from photo-corrosion. Combination of CdS and Ni2P increased absorption range of TiO2 at 720 nm. Holes and electrons produced during the photo-reaction can migrate to the CdS on the inside and to the Ni2P on the outside of the TiO2 protective coating. Such design exposes more surface, thus, increases hydrogen production.
关键词： template,hydrogen production,CdS@TiO2/Ni2P,hollow core-shell
更新于2025-09-23 15:21:01
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Improved visible-light photocurrent based on ZnO/ZnS core–shell nanorods via interfacial engineering
摘要： Vertically aligned quasi two-dimensional (2D) ZnO nanorods (NRs) on carbon fiber paper were prepared by a modified hydrothermal approach, an individual ZnO nanorod has a diameter of 100–200 nm and a length of ~1 μm. ZnO/ZnS core-hell hierarchal structures with an outer ZnS shell of ~25 nm were fabricated under an elaborate sulfidation treatment. Compared to ZnO NRs a depressed near band emission at 380 nm and a significant enhanced visible light emission around 500 nm were observed for the ZnO/ZnS core-hell NRs from photoluminescence spectra. XPS and ESR measurements were carried out to study the ions constituents and the defects of the prepared samples. The prepared samples were used as photoelectrodes in visible-light self-powered photoelectrochemical cell-type detector. And an enhanced photocurrent of 6.79 μA was obtained, which is ten times as high as that of the bare ZnO electrode. The results show that the existence of sulfur vacancies and the formation of ZnO/ZnS heterostructure were able to promote photocurrent performance, the former increases the carrier concentration and leads to an upshift of work function; the latter makes the band bend and the photogenerated e–p pairs can be separated efficiently. The results will be helpful to implement visible-light device based on heterostructure via interfacial engineering.
关键词： visible light,carbon paper,work function,photoelectrochemical cell-type detector,ZnO/ZnS core–shell
更新于2025-09-23 15:21:01