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Microwave Induced Center-Doping of Transition Metals Ions in Aqueous CdS NCs with Special Optical Properties
摘要： Under microwave irradiation, we systematically studied the formation of transition metal ions (TM), Ag+, Mn2+, Cu2+, Fe2+, Co2+ and Ni2+, doped CdS semiconductor nanocrystals in a pure water solution. The center-doping strategy is essential for achieving efficient internal-doping to improve the optical properties and stability of doped nanocrystals. The resulting TM doped nanocrystals have a high photoluminescence quantum yield (~ 60%) and an amazingly large range of the visible spectrum (480 ~ 650 nm). For Mn2+ doped CdS nanocrystals, significant high photoluminescence quantum yield, between 20% and 50% even at more than 600 nm, was achieved and there is potential for them to be directly used as a consummate toner for multicolor sensing and encoding without ligand exchange. Highly emissive-doped nanocrystals synthesized under designed conditions have been found to have excellent stability; samples could be stored for months without precipitation. In practice, this approach has great potential to promote the metal doping of various semiconductor nanocrystals to realize the specific advantages of doped nanocrystals in water solution.
关键词： transition metal ions,microwave,nanocrystals,doping,CdS
更新于2025-09-09 09:28:46
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Lead‐Free Semiconductors: Soft Chemistry, Dimensionality Control, and Manganese‐Doping of Germanium Halide Perovskites
摘要： Lead halide perovskites have drawn enormous interest due to their exceptional photovoltaic and optoelectronic properties. However, the toxic heavy metal lead is harmful to humans and the environment resulting in a need for strategies to replace this toxic element. Herein, we report a facile aqueous synthesis of CsGeX3 (X = I, Br) perovskite nanocrystals with size control achieved by varying the cysteammonium halide ligand concentration. We observe a variety of morphologies including pyramidal, hexagonal, and spheroidal. CsGeX3 nanocrystals undergo a lattice expansion due to partial replacement of Cs+ with larger cysteNH3+ cations into the lattice. We successfully dope Mn2+ into the CsGeX3 lattice for the first time with incorporation up to 29% in bulk and 16% in nano samples. XRD peak shifts and EPR hyperfine splitting strongly indicate that Mn2+ is doped into the lattice. Our results introduce a new member to the lead-free halide perovskite family and set the fundamental stage for their use in optoelectronic devices.
关键词： Germanium Halide Perovskites,Manganese(II) Doping,Perovskite Phases,Lead Substitution,Perovskite Nanocrystals
更新于2025-09-09 09:28:46
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Colloidal Crystals of NaYF <sub/>4</sub> Upconversion Nanocrystals Studied by Small-Angle X-Ray Scattering (SAXS)
摘要： Spherical NaYF4 upconversion nanocrystals with mean radii of about 5 and 11 nm are observed to form colloidal crystals, i.e., 3D assemblies of the particles with long-range order. The colloidal crystals of the larger particles form directly in solution when dispersions of the particles in toluene are stored at room temperature for several weeks. Crystallization of the smaller particles takes place when their dispersions in hexane are slowly dried at elevated temperatures. The formation and the structure of the colloidal crystals are studied by small-angle X-ray scattering (SAXS). SAXS measurements show that the smaller as well as the larger particles assemble into a face-centered cubic lattice with unit cell dimensions of a = 18.7 nm and a = 35.5 nm, respectively. The SAXS data also show that the particles in the colloidal crystals still bear a layer of oleic acid on their surfaces. The thickness of this layer is 1.5–1.8 nm, as determined by comparing the unit cell dimensions of the colloidal crystals with the mean particle sizes. The latter could be very precisely determined from the distinct oscillations observed in the SAXS data of dilute colloidal dispersions of the nanocrystals.
关键词： upconversion,colloidal crystals,nanocrystals,small-angle X-ray scattering
更新于2025-09-09 09:28:46
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Electronic, Structural and Vibrational Properties of GaP Diamondoids and Nanocrystals: A Density Functional Theory Study
摘要： The electronic, structural and vibrational properties of gallium phosphide diamondoids and nanocrystals were investigated using density functional theory at PBE/6-31(d) level, which included polarization functions. The energy gap obeyed the quantum confinement size effect with shape fluctuations. The gap converged towards its bulk limit at 2.26 eV. The Ga-P bond lengths of higher diamondoids were found to be distributed around the bulk experimental value at 2.36 Angstrom. Tetrahedral angles were found around the ideal bulk zincblende value at 109.47, degrees while dihedral angles were distributed around the ideal bulk zincblende values at ±60 and ±180 degree. These findings illustrate that diamondoids are a good representative of bulk structure. An analysis of vibrational modes, in terms of reduced masses, force constants and IR intensity, was then performed. The size-related change of certain vibrational frequencies of GaP diamondoids was compared with the experimental bulk. Radial breathing mode frequency began from 187 cm-1 for the smallest molecule GaPH6 and decreased with fluctuations, heading to 0 cm-1 as its bulk limit. Longitudinal optical mode began from 187 cm-1 for the smallest molecule and increased with fluctuations, heading to 376.9 cm-1 (11.3 THz) as its bulk limit. Hydrogen-related vibrations were relatively constant and can therefore be used to identify GaP diamondoids because of their high IR and Raman intensity peaks.
关键词： DFT,Diamondoids,Nanocrystals
更新于2025-09-09 09:28:46
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14.2: <i>Invited Paper:</i> Quantum Yield Measurement Using Organic Dyes as References for Semiconductor Nanocrystals
摘要： A method of using series of organic dyes as reference to measure the quantum yield efficiency (QY) for semiconductor nanocrystals (Quantum Dots, QDs) in solution state is reported. In the proposed method, the sensitivity of the fluorescence spectrophotometer on wavelength as well as the excitation power intensity is considered to improve the accuracy.
关键词： Semiconductor Nanocrystals,Quantum Dots,QDs,Quantum Yield Efficiency Measurment
更新于2025-09-09 09:28:46
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The peculiarities of structural and optical properties of HfO2-based films co-doped with silicon and erbium
摘要： The effect of deposition conditions and further annealing treatment on microstructure and optical properties of (Si,Er)-codoped HfO2 thin films is investigated. The films are grown on silicon substrates by RF magnetron co-sputtering of Si and erbium oxide pellets on a HfO2 target. As-deposited and annealed samples are examined by means of spectroscopic ellipsometry, Fourier transform infrared spectroscopy and photoluminescence method. It is demonstrated that the variation of RF power density allows monitoring the dopant content. An annealing of the samples at 800-1100°C for 10-60 min in nitrogen atmosphere results in the phase separation and the formation of HfO2, SiO2 and pure silicon phases. The films annealed at 900-950°C demonstrate the red luminescence that is ascribed to the carrier recombination in Si nanocrystals. Annealing at higher temperatures causes an enhancement of rare-earth luminescence under non-resonant excitation providing an additional argument toward the formation of silicon nanoclusters. The mechanism of the excitation of Er ions is found to be similar to that of Si-rich-SiO2 films doped with rare-earths. The Si nanocrystals are considered as the main sensitizer at visible excitation while the energy transfer from host defects dominates at ultraviolet-deep blue illumination.
关键词： erbium,hafnium oxide,silicon,nanocrystals,photoluminescence
更新于2025-09-09 09:28:46
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Quantum cutting properties of Tb3+/Yb3+ co-doped ZrO2-SiO2 nano-crystalized glasses synthesized via a sol-gel route
摘要： Tb3+/Yb3+ co-doped ZrO2-SiO2 nano-crystallized glasses were prepared by a sol-gel process. The crystal structure and optical properties including down-conversion photoluminescence (or, quantum cutting) of the Tb3+-Yb3+ system with respect to gel heat treatment temperature were investigated by X-ray diffraction (XRD), Raman, photoluminescence (PL), and PL decay curves analysis. The energy transfer efficiency from Tb3+ to Yb3+ ions, which converts one photon to two photons with lower energy, increased with heat-treatment temperature. Furthermore, the oxidation state of Tb4+ ions was suspected to influence the emission intensity of Tb3+ and energy conversion efficiency. Thus, a post-treatment reduction was applied to the sample heated at 1100 oC by annealing it at 1100 oC for 1 h under 5%H2/95%N2 reductive atmosphere. Consequently, the thermodynamically generated Tb4+ ions were reduced to a trivalent state, leading to higher energy transfer efficiency.
关键词： ZrO2 nanocrystals,Sol-gel method,photoluminescence,quantum cutting,Tb3+-Yb3+ pair,Tb4+ ions
更新于2025-09-09 09:28:46
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Synergistic Effect of the Electronic Structure and Defect Formation Enhances Photocatalytic Efficiency of Gallium Tin Oxide Nanocrystals
摘要： The design of photocatalysts with enhanced efficiency is pivotal to sustainable environmental remediation and renewable energy technologies. Simultaneous optimization of different factors affecting the performance of a photocatalyst, including the density of active surface sites, charge carrier separation, and valence and conduction band redox potentials, remains challenging. Here we report the synthesis of ternary gallium tin oxide (GTO) nanocrystals with variable composition, and investigate the role of Ga3+ dopants in altering the electronic structure of rutile-type SnO2 nanocrystal lattice using steady-state and time-resolved photoluminescence spectroscopies. Substitutional incorporation of Ga3+ increases the band gap of SnO2 nanocrystals, imparting the reducing power to the conduction band electrons, and causes the formation of acceptor states, which, in conjunction with electron trapping by donors (oxygen vacancies), leads to stabilization of the photoexcited carriers. Combination of a decrease in the charge recombination rate and adjustment of the conduction band reduction potential to more negative values synergistically promote the photocatalytic efficiency of the GTO nanocrystals. The apparent rate constant for the photocatalytic degradation of rhodamine-590 dye by optimally prepared GTO NCs is 0.39 min-1, more than two times greater than that by benchmark Aeroxide TiO2 P25 photocatalyst. The results of this work highlight the concept of using rational aliovalent doping of judiciously chosen metal oxide nanocrystal lattices to simultaneously manipulate multiple photocatalytic parameters, enabling the design of versatile and highly efficient photocatalysts.
关键词： photocatalysts,photocatalytic efficiency,nanocrystals,electronic structure,gallium tin oxide,defect formation
更新于2025-09-09 09:28:46
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Uniform Selenization of Crack-Free Films of Cu(In,Ga)Se2 Nanocrystals
摘要： Crack-free films of Cu(In,Ga)Se2 (CIGS) nanocrystals were deposited with uniform thickness (>1μm) on Mo-coated glass substrates using an ink-based, automated ultrasonic spray process, then selenized and incorporated into photovoltaic devices (PVs). The device performance depended strongly on the homogeneity of the selenized films. Cracks in the spray-deposited films resulted in uneven selenization rates and sintering by creating paths for rapid, uncontrollable selenium (Se) vapor penetration. To make crack-free films, the nanocrystals had to be completely coated with capping ligands in the ink. The selenization rate of crack-free films then depended on the thickness of the nanocrystal layer, the temperature, and duration of Se vapor exposure. Either inadequate or excessive Se exposure leads to poor device performance, generating films that were either partially sintered or exhibited significant accumulation of selenium. The deposition of uniform nanocrystal films is expected to be important for a variety of electronic and optoelectronic device applications.
关键词： Nanocrystals,Selenization,Copper Indium Gallium Selenide,CIGS,Photovoltaics
更新于2025-09-09 09:28:46
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Determination of Handedness in a Single Chiral Nanocrystal via Circularly Polarized Luminescence
摘要： The occurrence of biological homochirality is attributed to symmetry breaking mechanisms which are still debatable. Studies of symmetry breaking require tools for monitoring the population ratios of individual chiral nano-objects, such as molecules, polymers or nanocrystals. Moreover, mapping their spatial distributions may elucidate on their symmetry breaking mechanism. While luminescence is preferred for detecting single particle chirality due to its high signal to noise ratio, the typical low optical activity of chromophores limits its applicability. Here, we report on handedness determination of single chiral lanthanide based luminescent nanocrystals with a total photon count of 2×104. Due to the large emission dissymmetry we could determine the handedness of individual particles using only a single circular polarization component of the emission spectrum, without polarization modulation. A machine learning algorithm, trained to several spectral lineshape features, enabled us to determine and spatially map the handedness of individual nanocrystals with high accuracy and speed. This technique may become invaluable in studies of symmetry breaking in chiral materials.
关键词： chiroptical activity,circularly polarized luminescence,lanthanide nanocrystals,single-particle spectroscopy
更新于2025-09-09 09:28:46