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The mechanochemical synthesis of PbTe nanostructures: following the Ostwald ripening effect during milling
摘要： A fundamental understanding of the Ostwald ripening effect (ORE) during the mechanochemical synthesis of PbTe nanostructures is presented. The ripening process involves the coarsening of larger particles from those of smaller size; this phenomenon was systematically evaluated at different stages of milling by microscopy analyses (AFM, TEM, STEM and HRTEM). At the early stage of milling, smaller particles and quantum dots are eventually dissolved to lower the total energy associated with their surfaces. The ripening process – during milling – involves short-range mass transfer among particles. HRTEM analyses allowed us to identify that coarsening occurs by thermo-mechanically activated cooperative mechanisms. The detachment of the atoms from smaller particles to form bigger ones plays a major role in the particle coarsening. It was found that the coarsening process was not limited to crystalline nanostructures; so grain boundaries, edge dislocations and boundaries among crystalline and amorphous phases also play an important role to determine how species migration contributes to generate coarse particles. Those serve as sites for inducing coarsening in an equivalent way as surfaces do. Secondary ion mass spectrometry and elemental chemical mapping (EDX-STEM) revealed that both the purity and the chemical homogeneity of the PbTe nanostructures are prominent features of this material. Additionally, a direct band gap enhancement (780 nm) compared to bulk PbTe (3859 nm) was detected. It occurred due to the quantum confinement effect, lattice imperfections and even surface properties of the nanostructures. It is important to point out that the whole optical behaviour of the PbTe nanostructures was dependent upon the embedded nanoparticles and quantum dots in the clusters and coarse particles ranging from 15 nm to 35 nm.
关键词： PbTe nanostructures,microscopy analyses,quantum confinement effect,mechanochemical synthesis,Ostwald ripening effect,high-energy milling
更新于2025-09-19 17:15:36
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Phonon and Polaron properties in InSb spherical quantum dots
摘要： The size-dependent energy gaps, electron and heavy hole effective masses, phonon frequencies and polaron related parameters in InSb spherical quantum dots are investigated. The calculations are performed using a pseudopotential approach. Good agreement is obtained between our results and those of the literature for bulk InSb. When proceeding from bulk to nano-scale, all studied properties are found to be changed significantly. This is attributed to the quantum confinement effect.
关键词： Polarons,Phonons,Quantum dots,InSb,Quantum confinement
更新于2025-09-19 17:13:59
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Ag2ZnSnS4 Nanocrystals Expand the Availability of RoHS Compliant Colloidal Quantum Dots
摘要： The demonstration of the quantum confinement effect in colloidal quantum dots (QDs) has been extensively studied and exploited mainly in Pb and Cd chalcogenide systems. There has been an urgent need recently for the development of non(less)-toxic colloidal QDs to warrant compliance with current safety regulations (Restriction of Hazardous Substances (RoHS) Directive 2002/95/EC). Herein, we report Pb/Cd-free, solution processed luminescent Ag2ZnSnS4 (AZTS) colloidal QDs. We present a selective and controlled amine and thiol-free synthesis of air stable luminescent Ag2ZnSnS4 QDs by hot injection technique. By controlling the reaction conditions we obtain controlled size variation, and demonstrate the quantum confinement effect that is in good agreement with the theoretically calculated values. The bandgap of the AZTS QDs is size-tunable in the near infrared from 740 nm to 850 nm. Finally, we passivate the surface with Zn-oleate, which yields higher quantum yield (QY), longer lifetime and better colloidal stability.
关键词： near infrared,RoHS compliant,Ag2ZnSnS4,colloidal quantum dots,quantum confinement,Zn-oleate passivation
更新于2025-09-19 17:13:59
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Role of nitrogen doped carbon quantum dots on CuO nano-leaves as solar induced photo catalyst
摘要： A p-type transition metal oxide, copper oxide (CuO) was modified with nitrogen doped carbon quantum dots (NCQDs) to fabricate an effective CuO/NCQDs solar driven photo catalyst. The fabrication of single phase monoclinic CuO was confirmed by XRD. SEM images showed the leaf like morphology for CuO which appeared rough and densely packed in CuO/NCQDs composites. TEM images of CuO/NCQDs shows slightly distorted nano-leaves with NCQDs dispersed on them. HRTEM of CuO/NCQDs shows fringes with characteristic planes confirming that the addition of NCQDs has not distorted the crystal structure of CuO. SAED of CuO/NCQDs further confirms the crystalline nature of the as synthesized composite photo catalyst by exhibiting bright diffraction rings. These results further supported the XRD data. EDS spectra of NCQDs and CuO/NCQDs confirm the formation of pure nitrogen doped carbon quantum dots and Cu, N, C and O atoms confirming that NCQDs are well incorporated on CuO Nano leaves. UV-Vis spectra showed a slight increase of band gap energies due to quantum confinement effects. PL spectra exhibited decreased photoluminescence intensity indicating suppression of recombination rate. The developed photocatalyst was applied for the degradation of harmful dye methyl orange. The composite catalyst showed superior degradation efficiency as compared to pure CuO nano-leaves attributed to enhanced visible light absorption and better charge separation ability due to introduction of NCQDs.
关键词： solar light catalyst,nitrogen doped quantum dots,charge separation efficiency,quantum confinement effect,CuO nano-leaves
更新于2025-09-19 17:13:59
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Nonradiative Energy Transfer between Thickness-Controlled Halide Perovskite Nanoplatelets
摘要： Despite showing great promise for optoelectronics, the commercialization of halide perovskite nanostructure-based devices is hampered by inefficient electrical excitation and strong exciton binding energies. While transport of excitons in an energy-tailored system via F?rster resonance energy transfer (FRET) could be an efficient alternative, halide ion migration makes the realization of cascaded structures difficult. Here, we show how these could be obtained by exploiting the pronounced quantum confinement effect in two-dimensional CsPbBr3-based nanoplatelets (NPls). In thin films of NPls of two predetermined thicknesses, we observe an enhanced acceptor photoluminescence (PL) emission and a decreased donor PL lifetime. This indicates a FRET-mediated process, benefitted by the structural parameters of the NPls. We determine corresponding transfer rates up to kFRET = 0.99 ns?1 and efficiencies of nearly ηFRET = 70%. We also show FRET to occur between perovskite NPls of other thicknesses. Consequently, this strategy could lead to tailored energy cascade nanostructures for improved optoelectronic devices.
关键词： nanoplatelets,quantum confinement,FRET,halide perovskite,optoelectronics
更新于2025-09-19 17:13:59
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Zn1 a?? xCdxS Nanoparticles Obtained by Laser Ablation
摘要： Approximately spherical nanoparticles of the II–VI semiconductor materials Zn1 – xCdxS have been produced successfully by laser ablation of the bulk material in several liquids. The non-stabilized suspensions of particles are characterized by absorption spectroscopy and transmission electron microscopy (TEM). The procedure is not strongly size-selective, radii of 7 ± 3 nm were found for Zn1 – xCdxS by transmission electron microscopy. Acetonitrile stabilizes the particles for several days up to weeks. Prolonged irradiation leads effectively to a reduction in particles size, in which particle agglomeration may play an important role. Ablation in degassed liquids does not have a significant effect on the absorption of the suspended particles.
关键词： Zn1 – xCdxS nanoparticles,laser ablation,absorption spectroscopy,transmission electron microscopy,quantum confinement
更新于2025-09-19 17:13:59
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Perovskite quantum dots for light-emitting devices
摘要： Perovskite quantum dots (QDs) have been hotly pursued in recent decades owing to their quantum confinement effect and defect-tolerant nature. Their unique optical properties, such as high photoluminescence quantum yield (PLQY) approaching unity, narrow emission bandwidth, tunable wavelength spanning the entire visible spectrum, and compatibility with flexible/stretchable electronics, render perovskite QDs promising for next-generation solid lighting sources and information displays. Herein, the advances in perovskite QDs and their applications in LEDs are reviewed. Strategies to fabricate efficient perovskite QDs and device configuration, including material composition design, synthetic methods, surface engineering, and device optimization, are investigated and highlighted. Moreover, the main challenges in perovskite QDs of instability and toxicity (lead-based) are identified, while the solutions undertaken with respect to composition engineering, device encapsulation, and lead-replacement QDs are demonstrated. Meanwhile, perspectives for the further development of perovskite QDs and corresponding LEDs are presented.
关键词： device encapsulation,quantum confinement,Perovskite quantum dots,LEDs,instability,composition engineering,flexible electronics,photoluminescence,lead-replacement,stretchable electronics,toxicity,light-emitting devices
更新于2025-09-16 10:30:52
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Size-controlled excitonic effects on electronic and optical properties of Sb <sub/>2</sub> S <sub/>3</sub> nanowires
摘要： In this work, the electronic and optical properties of one-dimensional (1D) Sb2S3 nanowires (NWs) with different sizes are investigated using first-principles calculations. The indirect–direct band transition of Sb2S3 NWs can be tuned effectively by the NW size and various uniaxial strains. In the Sb2S3 NWs, the quantum confinement effects result in wider bandgaps while the significantly enhanced electron–hole interaction that is expected to produce excitonic bound states generates a bandgap narrowing. The exciton binding energies for the Sb2S3 NWs are predicted by the effective masses of electrons and holes to lie in the range of 0–1 eV, which are larger than that of bulk Sb2S3, suggesting that excitons in Sb2S3 NWs may bind possible defects to promote luminescence. The size-controlled absorption edge blueshift and redshift of Sb2S3 NWs suggest that Sb2S3 NWs may be promising in the applications of nanoscale light emitting devices.
关键词： optical properties,first-principles calculations,quantum confinement effects,light emitting devices,electronic properties,exciton binding energies,Sb2S3 nanowires
更新于2025-09-16 10:30:52
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Quantum Confinement Induced Excitonic Mechanism in Zinc-Oxide-Nanowalled Microrod Arrays for UV–Vis Surface-Enhanced Raman Scattering
摘要： We studied surface-enhanced Raman spectroscopy (SERS) in 4-mercaptopyridine (4-Mpy) deposited on zinc oxide (ZnO) nanostructures, by using resonance Raman scattering covering a range of incident photon energies from 1.7 to 5.7 eV. We investigated all primary routes of the energy-specific resonances that are associated with the electronic transitions between the ZnO valence band (VB) to the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) to the ZnO conduction band (CB), respectively. Two resonances at 5.55 and 5.15 eV in the ultraviolet (UV) spectral range can be associated with transitions into the CB and most importantly into an excitonic-related state below the ZnO CB, respectively. The energy difference between the UV resonances is 0.4 eV corresponding to the excitonic binding energy as a result of excitonic quantum confinement in the 10?20 nm thick ZnO nanowalls. The observed excitonic SERS resonance enhancement of the ring-breathing mode of 4-Mpy is about 15 times stronger than for the VB resonance observed at 2.43 eV and free of luminescence background. Hence, we outline new pathways of improving the detectability of molecules by chemical SERS due to tuning of the quantum confinement in the excitonic resonance enhancement.
关键词： quantum confinement,surface-enhanced Raman spectroscopy,excitonic mechanism,UV-Vis,ZnO,SERS,zinc oxide
更新于2025-09-16 10:30:52
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Facile Preparation of Molybdenum Disulfide Quantum Dots Using a Femtosecond Laser
摘要： Molybdenum disulfide (MoS2) is rapidly emerging in a wide range of applications owing to its superior optical, electrical, and catalytic properties. In particular, aside from the current great interest in monolayer MoS2, MoS2 quantum dots (QDs) have received much attention in the electronics and optoelectronics fields owing to their inherent electrical and optical properties arising from the quantum confinement effect. Thus, various methods for producing MoS2 QDs, such as exfoliation, substrate growth, and colloidal synthesis, have been attempted. In this study, the method for manufacturing MoS2 QD with a size of 10 nm which is simpler than the conventional method was devised. On the basis of characterization of the prepared MoS2 QD samples, resistive switching devices was fabricated. These devices demonstrated stable unipolar resistive switching behavior without an electroforming process. This study provides a new approach for the mass production of MoS2 QD and one of their potential applications.
关键词： exfoliation,memristor,MoS2,quantum confinement effect,phase transition
更新于2025-09-16 10:30:52