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S, N co-doped graphene quantum dots-induced ascorbic acid fluorescent sensor: Design, characterization and performance
摘要： In this work, new detection route for ascorbic acid was designed. First, highly luminescent sulfur and nitrogen doped graphene quantum dots (S,N-GQDs) were prepared via simple hydrothermal method using citric acid and thiourea as the C, N and S sources respectively. The prepared S,N-GQDs are characterized by XRD, HRTEM, FTIR, EDS and PL. Investigations showed that prepared S,N-GQDs have a good photostability and excitation-dependent emission fluorescence. Prepared S,N-GQDs showed maximum excitation wavelength and emission wavelength at 400 and 462nm, respectively. In the following, prepared S,N-GQDs were applied as a photoluminescence probe for detection of ascorbic acid (AA). The designed sensor was based on “off-on” detection mode. The developed sensor had a linear response to AA over a concentration range of 10-500μM with a detection limit of 1.2μM. The regression equation is Y = 0.0014 X+1.2036, where Y and X denote the fluorescence peak intensity and AA concentration, respectively.
关键词： Graphene quantum dots,Quantum confinement,Fluorescence sensor,Nanostructures,Water-soluble vitamin,Quenching
更新于2025-11-14 15:32:45
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Increasing photoluminescence quantum yield by nanophotonic design of quantum-confined halide perovskite nanowire arrays
摘要： High photoluminescence quantum yield (PLQY) is required to reach optimal performance in solar cells, lasers and light-emitting diodes (LEDs). Typically, PLQY can be increased by improving the material quality to reduce the non-radiative recombination rate. It is in principle equally effective to improve the optical design by nanostructuring a material to increase light out-coupling efficiency and introduce quantum confinement, both of which can increase the radiative recombination rate. However, increased surface recombination typically minimizes nanostructure gains in PLQY. Here a template guided vapor phase growth of CH3NH3PbI3 (MAPbI3) nanowire (NW) arrays with unprecedented control of NW diameter from the bulk (250 nm) to the quantum confined regime (5.7 nm) is demonstrated, while simultaneously providing a low surface recombination velocity of 18 cm s-1. This enables a 56-fold increase in the internal PLQY, from 0.81 % to 45.1 %, and a 2.3-fold increase in light out-coupling efficiency to increase the external PLQY by a factor of 130, from 0.33 % up to 42.6 %, exclusively using nanophotonic design.
关键词： light out-coupling,photoluminescence quantum yield,quantum confinement,perovskite,photodetector
更新于2025-11-14 15:28:36
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Crystalline Semiconductor Boron Quantum Dots
摘要： Zero-dimensional boron structures have always been the focus of theoretical research owing to its abundant phase structures and special properties. Boron clusters have been reported extensively by combining structure searching theories and photoelectron spectroscopy experiments, however, crystalline boron quantum dots (BQDs) have rarely been reported. Here we report the preparation of large-scale and uniform crystalline semiconductor BQDs from the expanded bulk boron powders via a facile and efficient probe ultrasonic approach in acetonitrile solution. The obtained BQDs have 2.46 nm in an average lateral size and 2.81 nm in thickness. Optical measurements demonstrate that strong quantum confinement effect occurs in the BQDs, implying the increase of the bandgap from 1.80 eV for the corresponding bulk to 2.46 eV for the BQDs. By injecting the BQDs into polyvinylpyrrolidone as an active layer, a BQDs-based memory device is fabricated which shows a rewriteable nonvolatile memory effect with a low transition voltage of down to 0.5 V and a high ON/OFF switching ratio of 103 as well as a good stability.
关键词： ultrasound,quantum dots,nonvolatile memory device,quantum confinement effect,boron
更新于2025-11-14 15:23:50
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Quantum and Dielectric Confinement Effects in Lower-Dimensional Hybrid Perovskite Semiconductors
摘要： Hybrid halide perovskites are now superstar materials leading the field of low-cost thin film photovoltaics technologies. Following the surge for more efficient and stable 3D bulk alloys, multilayered halide perovskites and colloidal perovskite nanostructures appeared in 2016 as viable alternative solutions to this challenge, largely exceeding the original proof of concept made in 2009 and 2014, respectively. This triggered renewed interest in lower-dimensional hybrid halide perovskites and at the same time increasingly more numerous and differentiated applications. The present paper is a review of the past and present literature on both colloidal nanostructures and multilayered compounds, emphasizing that availability of accurate structural information is of dramatic importance to reach a fair understanding of quantum and dielectric confinement effects. Layered halide perovskites occupy a special place in the history of halide perovskites, with a large number of seminal papers in the 1980s and 1990s. In recent years, the rationalization of structure–properties relationship has greatly benefited from new theoretical approaches dedicated to their electronic structures and optoelectronic properties, as well as a growing number of contributions based on modern experimental techniques. This is a necessary step to provide in-depth tools to decipher their extensive chemical engineering possibilities which surpass the ones of their 3D bulk counterparts. Comparisons to classical semiconductor nanostructures and 2D van der Waals heterostructures are also stressed. Since 2015, colloidal nanostructures have undergone a quick development for applications based on light emission. Although intensively studied in the last two years by various spectroscopy techniques, the description of quantum and dielectric confinement effects on their optoelectronic properties is still in its infancy.
关键词： quantum confinement,multilayered perovskites,structural engineering,colloidal nanostructures,hybrid halide perovskites,optoelectronic properties,2D materials,dielectric confinement
更新于2025-09-23 15:23:52
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Bulk Assembly of Corrugated 1D Metal Halides with Broadband Yellow Emission
摘要： The family of molecular level low-dimensional organic metal halide hybrids has expanded significantly over the last few years. Here a new type of 1D metal halide structure is reported, in which metal halide octahedra form a corrugated double-chain structure via nonplanar edge-sharing. This material with a chemical formula of C5H16N2Pb2Br6 exhibits a broadband yellow emission under ultraviolet light excitation with a photoluminescence quantum efficiency of around 10%. The light-yellow emission is considered to be attributed to self-trapping excitons. Theoretical calculations show that the unique alignment of the octahedra leads to small band dispersion and large exciton binding energy. Together with previously reported 1D metal halide wires and tubes, this new bulk assembly of 1D metal halides suggests the potential to develop a library of bulk assemblies of metal halides with controlled structures and compositions.
关键词： photoluminescence,quantum confinement effect,exciton self-trapping,organic metal halide hybrids,1D structures
更新于2025-09-23 15:22:29
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Visible-Light Driven Photocatalytic Hydrogen Generation by Water-Soluble All-Inorganic Core-Shell Silicon Quantum Dots
摘要： The photocatalytic hydrogen (H2) generation by boron (B) and phosphorus (P) codoped silicon quantum dots (Si QDs) with diameters in the quantum confinement regime is investigated. The codoped Si QDs have an amorphous shell made from B, Si and P. The shell induces negative potential on the surface and makes codoped Si QDs dispersible in water. The hydrophilic shell offers enhanced stability and efficiency in the photocatalytic H2 generation and provides the opportunity to study the size dependence of the H2 generation rate. A drastic increase of the H2 generation rate with decreasing the QD size is observed. Analyses based on the Marcus theory reveal that the upper shift of the lowest unoccupied molecular orbital level of Si QDs by the quantum confinement effect is responsible for the enhanced photocatalytic activity.
关键词： silicon quantum dots,quantum confinement,Marcus theory,photocatalytic hydrogen generation
更新于2025-09-23 15:21:01
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Graphene for Flexible Lighting and Displays || Graphene-based quantum dot emitters for light-emitting diodes
摘要： Quantum dot is a zero-dimensional material that is introduced from the quantum con?nement effect when it is sized in nanometer scale and has various electrical and optical properties depending on the size of the particle. The electrons con?ned in small areas of nanoscale which are smaller than exciton Bohr radius are quantized and limited in free motion, and electrons in quantum dot are con?ned in every three direction by the quantum con?nement effect which causes a ?nite number of electron, hole, and exciton states, resulting in various characteristics on the size of the particle. In other words, the full con?nement in every three direction results in the complete quantization or discretization of the energy states of con?ned charge carriers in quantum dot [1]. Therefore, the fewer energy levels are quanti?ed as the energy level of the carrier decreases as the particle size decreases, resulting in a wider and more discretized bandgap [2e4].
关键词： electroluminescence,light-emitting diodes,quantum confinement,graphene quantum dots,photoluminescence
更新于2025-09-23 15:21:01
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Nanoshell quantum dots: Quantum confinement beyond the exciton Bohr radius
摘要： Nanoshell quantum dots (QDs) represent a novel class of colloidal semiconductor nanocrystals (NCs), which supports tunable optoelectronic properties over the extended range of particle sizes. Traditionally, the ability to control the bandgap of colloidal semiconductor NCs is limited to small-size nanostructures, where photoinduced charges are confined by Coulomb interactions. A notorious drawback of such a restricted size range concerns the fact that assemblies of smaller nanoparticles tend to exhibit a greater density of interfacial and surface defects. This presents a potential problem for device applications of semiconductor NCs where the charge transport across nanoparticle films is important, as in the case of solar cells, field-effect transistors, and photoelectrochemical devices. The morphology of nanoshell QDs addresses this issue by enabling the quantum-confinement in the shell layer, where two-dimensional excitons can exist, regardless of the total particle size. Such a geometry exhibits one of the lowest surface-to-volume ratios among existing QD architectures and, therefore, could potentially lead to improved charge-transport and multi-exciton characteristics. The expected benefits of the nanoshell architecture were recently demonstrated by a number of reports on the CdSbulk/CdSe nanoshell model system, showing an improved photoconductivity of solids and increased lifetime of multi-exciton populations. Along these lines, this perspective will summarize the recent work on CdSbulk/CdSe nanoshell colloids and discuss the possibility of employing other nanoshell semiconductor combinations in light-harvesting and lasing applications.
关键词： Optoelectronic properties,Nanoshell quantum dots,CdSbulk/CdSe nanoshell,Colloidal semiconductor nanocrystals,Quantum confinement
更新于2025-09-23 15:19:57
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Quantum size effect and surface defect passivation in size-controlled CsPbBr3 quantum dots
摘要： Luminescent CsPbBr3 quantum dots (QDs) with adjustable size and bandgap were grown by controlling the synthesis temperature in this paper. As the synthesis temperature increases, the QD size becomes larger and then smaller. The corresponding absorption and steady-state photoluminescence spectrum indicate that the QD band gap becomes smaller and then larger, which is a typical quantum confinement effect. Time-resolved photoluminescence spectrum and femtosecond transient absorption spectrum (fs-TAS) show that the non-radiative recombination probability of photocarriers in small QDs is small it has few defects, indicating that the ligand molecules adsorbed on the surface of QDs effectively passivate the surface defects of CsPbBr3. Finally, the hot-phonon bottleneck effect of CsPbBr3 QDs is revealed by the kinetic curves fitting of fs-TAS and the cooling kinetic process of hot carriers is also discussed in detail. This work provides new insights on size-dependent photophysical properties of CsPbBr3 QDs.
关键词： Quantum confinement effect,Metal halide perovskite QDs,Defect passivation,Hot carriers
更新于2025-09-23 15:19:57
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Blue-emitting and self-assembled thinner perovskite CsPbBr <sub/>3</sub> nanoplates: Synthesis and formation mechanism
摘要： Low dimensional semiconductor nanomaterials have a great promise for a variety of applications due to their size-dependent and excellent optoelectronic properties. In this work, we developed a strategy to synthesize uniform and very thin CsPbBr3 perovskite nanoplates (NPls) by introducing additional metal bromides. The CsPbBr3 NPls, self-assembled to a face-to-face stacked state, had a thickness of 4.4 nm (equal to only 2 monolayers, 2 MLs) and showed a maximum emission at 437 nm and a narrow FWHM of 14 nm. The formation mechanism of the CsPbBr3 NPls by adding FeBr3 was ascribed to the constrained growth of CsPbBr3 nanocubes when the surface of Cs+ ions was substituted by the protonated oleylammonium from the byproduct OLA-HBr.
关键词： blue-emitting,quantum confinement,self-assembly,CsPbBr3,perovskite nanoplates
更新于2025-09-23 15:19:57