- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Enhanced upconversion luminescence in NaYF<sub>4</sub>:Yb,Er nanoparticles by using graphitic carbon shells
摘要： Upconversion nanoparticles (UCNPs) have drawn much attention in the past decade due to their superior physicochemical features and great potential in biomedical. However, practical applications of upconversion luminescence are often limited by its relatively low luminescence efficiency. In this paper, we designed and synthesized NaYF4:Yb,Er nanoparticles using a hydrothermal approach, and thereafter it was coated with a thin layer of graphitic carbon to form a core/shell nanostructure via a controlled chemical vapor deposition process. It is shown that Yb and Er doped in the crystal of NaYF4 in the forms of Yb3+ and Er3+. The thickness of the graphitic carbon shell is close to 0.45 nm, and this corresponds between one and two atomic layers. The graphitic carbon shell not only leads to a significant enhancement in the emission intensity but also provide a longer luminescence decay lifetime compared to bare NaYF4:Yb,Er nanoparticles. Our finding provides a new strategy to remarkably improve fluorescence upconversion, and opportunities for diverse applications requiring high fluorescence intense.
关键词： Functional application,Optical properties,Nanocomposites,Gas phase reaction
更新于2025-09-23 15:22:29
-
Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F<sup>−</sup>
摘要： Anion photoelectron imaging is a very efficient method for the study of energy states of bound negative ions, neutral species and interactions of unbound electrons with neutral molecules/atoms. State-of-the-art in vacuo anion generation techniques allow application to a broad range of atomic, molecular, and cluster anion systems. These are separated and selected using time-of-flight mass spectrometry. Electrons are removed by linearly polarized photons (photo detachment) using table-top laser sources which provide ready access to excitation energies from the infra-red to the near ultraviolet. Detecting the photoelectrons with a velocity mapped imaging lens and position sensitive detector means that, in principle, every photoelectron reaches the detector and the detection efficiency is uniform for all kinetic energies. Photoelectron spectra extracted from the images via mathematical reconstruction using an inverse Abel transformation reveal details of the anion internal energy state distribution and the resultant neutral energy states. At low electron kinetic energy, typical resolution is sufficient to reveal energy level differences on the order of a few millielectron-volts, i.e., different vibrational levels for molecular species or spin-orbit splitting in atoms. Photoelectron angular distributions extracted from the inverse Abel transformation represent the signatures of the bound electron orbital, allowing more detailed probing of electronic structure. The spectra and angular distributions also encode details of the interactions between the outgoing electron and the residual neutral species subsequent to excitation. The technique is illustrated by the application to an atomic anion (F?), but it can also be applied to the measurement of molecular anion spectroscopy, the study of low lying anion resonances (as an alternative to scattering experiments) and femtosecond (fs) time resolved studies of the dynamic evolution of anions.
关键词： Chemical physics,Chemistry,gas phase anions,physical chemistry,Issue 137,electronic structure,velocity mapped imaging,photoelectron spectroscopy
更新于2025-09-23 15:22:29
-
Importance of carbon-monoxide-induced reaction in microwave heating synthesis of β-SiC from silicon powder in air
摘要： Microwave heating is known to provide extremely rapid synthesis of silicon carbide (SiC) from mixtures of silicon and carbon powders. The formation mechanism has long been considered to be a solid-state reaction among the powders in the mixture. Here, we present a new reaction mechanism via a gas-phase route. We have confirmed successful synthesis of ￠-SiC powder by microwave-heating of a small amount of Si powder that was entered into a quartz tube and then embedded in graphite powder, although no direct contact between the Si and graphite powders was allowed. Scanning electron microscopy observations revealed that the ￠-SiC powder was formed by direct carbonization of the Si powder. Since the atmosphere during the reaction comprises a vast majority of carbon monoxide (CO) gas according to the Boudouard equilibrium, the carbonization appears to have taken place via the CO gas. The contribution of such a gas-phase reaction could account in part for the rapidity of the microwave-heating reactions reported so far, which can hardly be explained solely by solid-state reactions among the mixed powders.
关键词： Carbon monoxide,Gas-phase reaction,Microwave heating,Silicon carbide,Air atmosphere,Silicon
更新于2025-09-23 15:21:21
-
Laser-Induced Dissociation of the Monolayer of Adsorbed Methanol Molecules
摘要： Astronomical observations indicate a high abundance of methanol molecules in the gas phase of molecular-cloud dense cores, which cannot be explained by gas-phase chemical reactions only. A significant contribution to the methanol abundance should be provided by chemical reactions on the dust particle surface with subsequent desorption of the produced molecules into the gas phase. For the development and refinement of models involving these processes, laboratory studies of photo-induced processes occurring in the adsorbed material are necessary. In this paper, the experiment results of adsorbed methanol molecules are presented. A methanol molecule monolayer, physically adsorbed on fused silica surface cooled by liquid nitrogen (Т ～ 100 K), was irradiated in high vacuum by nanosecond pulses of an excimer KrF laser with a fixed wavelength λ = 248 nm. The photodissociation products of three-photon laser excitation were recorded by a quadrupole mass spectrometer. Relative yields of photofragments H, OH, and CH3 were determined. Photolysis of partially deuterated CH3OH molecules has shown that hydrogen atoms can be ejected both from hydroxyl and methyl groups. In contrast to the isolated molecule photolysis in the gas phase and dissociation of the multilayer molecular coatings, photoexcitation of adsorbed methanol monolayer even in the energy region of 10 eV does not cause noticeable chemical transformations and does not lead to the formation of molecular components H2 and CH4. Due to existing astrochemical modeling problems, possible application methods of the obtained laboratory results are considered.
关键词： chemical reactions,astronomical observations,adsorbed monolayer,mass spectrometry,photo-induced processes,gas phase,dust particle surface,KrF laser,photodissociation,methanol
更新于2025-09-23 15:21:01
-
Influence of polymeric template impurities on photocatalytic properties of bulk macroporous TiO2 under visible light irradiation in the gas phase oxidation of acetone
摘要： Macroporous oxides are often prepared by template method with polymeric spheres, however, these polymeric spheres synthesized by emulsion polymerization using different initiators, most commonly contain S or/and N chemical residues. We have found that these template-originated impurities are not completely removed after thermal treatment of composites at ~ 500 °C, thus, influencing surface acidic properties and photocatalytic performance of the catalysts. The research is focused on the influence of different types of chemical residues left after incomplete polymer elimination on photocatalytic activity.
关键词： Visible light,Gas-phase oxidation,Macroporous TiO2,Template-assisted method,Photocatalysis
更新于2025-09-19 17:15:36
-
Conformational assignment of gas phase peptides and their H-Bonded complexes using far-IR/THz: IR- UV ion dip experiment, DFT-MD spectroscopy, and Graph Theory for modes assignment.
摘要： The combined approach of gas phase IR-UV ion dip spectroscopy experiments and DFT-based molecular dynamics simulations for theoretical spectroscopy reveals the 3D structures of (Ac-Phe-OMe)1,2 peptides using the far-IR/THz signatures. Both experimental and simulated IR spectra are well-resolved in the 100-800 cm?1 domain, allowing an unambiguous assignment of the conformers, that could not be achieved in other more congested spectral domains. We also present and make proofs-of-principles for our newly developed theoretical method for the assignment of (anharmonic) vibrational modes from MD simulations based on Graph Theory coupled to APT weighted-internal coordinates velocities DOS spectra. The principles of the method are reviewed, applications to the simple gas phase water and NMA (N-Methyl-Acetamide) molecules are presented, and the application to the more complex (Ac-Phe-OMe)1,2 peptidic systems shows that the complexity in assigning vibrational modes from MD simulations is released with the graphs. Our newly developed graph-based methodology is furthermore shown to allow an easy comparison between the vibrational modes of isolated monomer(s) and their complexes, as illustrated by the (Ac-Phe-OMe)1,2 peptides.
关键词： gas phase peptides,vibrational modes assignment,far-IR/THz spectroscopy,Graph Theory,IR-UV ion dip,DFT-MD simulations,β-sheet structures
更新于2025-09-19 17:15:36
-
In situ FTIR reactor for monitoring gas phase products during a (photo)catalytic reaction in the liquid phase
摘要： Various catalytic and photocatalytic reactions in the liquid phase give rise to gas products. Therefore, the identification and quantification of these products are of high importance and even essential for some reactions. In this communication, a new in situ FTIR reactor is designed and used for analyzing the gas headspace of a (photo)catalytic reaction in solution. It allows the identification and quantification of the gas products of a liquid reaction under operating conditions and in real time. The new reactor has been tested in three representative photocatalytic reactions widely studied as model reactions in the liquid phase, i.e., i) decomposition of formic acid, ii) oxidation of Methylene Blue and iii) reduction of CO2. The validity of the results has been confirmed by analyzing the headspace at the end of the reaction using GC. The new reactor opens the possibility to follow on-line the (photo)catalyst activity. This is useful for ensuring the stability of the catalyst and studying the evolution of the selectivity during the reaction. The non-destructive behavior of the FTIR technique allows its coupling with other techniques for obtaining complementary results. The new reactor setup is easy to handle, to ship, and is very efficient which make it very suitable for performing fast and/or preliminary studies.
关键词： gas phase products,photocatalytic reaction,liquid phase,real-time analysis,FTIR reactor
更新于2025-09-10 09:29:36
-
Effect of the Preparation Method (Sol-Gel or Hydrothermal) and Conditions on the TiO2 Properties and Activity for Propene Oxidation
摘要： Since the two most commonly used methods for TiO2 preparation are sol-gel (SG) and hydrothermal (HT) synthesis, this study attempts to compare both methods in order to determine which one is the most suitable to prepare photocatalysts for propene oxidation. In addition, this work studies how the concentration of the HCl used for hydrolysis of the TiO2 precursor affects the properties of the obtained materials. Also, the effect of avoiding the post-synthesis heat-treatment in a selection of samples is investigated. The photocatalysts are characterized by XRD, N2 adsorption-desorption isotherms and UV-vis spectroscopy, and the study tries to correlate the properties with the photocatalytic performance of the prepared TiO2 samples in propene oxidation. TiO2 materials with high crystallinity, between 67% and 81%, and surface area (up to 134 m2/g) have been obtained both by SG and HT methods. In general, the surface area and pore volume of the TiO2-HT samples are larger than those of TiO2-SG ones. The TiO2-HT catalysts are, in general, more active than TiO2-SG materials or P25 in the photo-oxidation of propene. The effect of HCl presence during the TiO2 synthesis and of the post synthesis heat treatment are much more marked in the case of the SG materials.
关键词： TiO2 synthesis method,HCl,VOCs elimination,photocatalysis,gas phase
更新于2025-09-10 09:29:36
-
Coherent multidimensional spectroscopy of dilute gas-phase nanosystems
摘要： Two-dimensional electronic spectroscopy (2DES) is one of the most powerful spectroscopic techniques with unique sensitivity to couplings, coherence properties and real-time dynamics of a quantum system. While successfully applied to a variety of condensed phase samples, high precision experiments on isolated systems in the gas phase have been so far precluded by insufficient sensitivity. However, such experiments are essential for a precise understanding of fundamental mechanisms and to avoid misinterpretations. Here, we solve this issue by extending 2DES to isolated nanosystems in the gas phase prepared by helium nanodroplet isolation in a molecular beam-type experiment. This approach uniquely provides high flexibility in synthesizing tailored, quantum state-selected model systems of single and many-body character. In a model study of weakly-bound Rb2 and Rb3 molecules we demonstrate the method’s unique capacity to elucidate interactions and dynamics in tailored quantum systems, thereby also bridging the gap to experiments in ultracold quantum science.
关键词： Two-dimensional electronic spectroscopy,helium nanodroplet isolation,gas-phase nanosystems,ultracold quantum science,Rb2 and Rb3 molecules
更新于2025-09-10 09:29:36
-
Static and dynamic phases of a Tonks–Girardeau gas in an optical lattice
摘要： We investigate the properties of a Tonks–Girardeau gas in the presence of a one-dimensional lattice potential. Such a system is known to exhibit a pinning transition when the lattice is commensurate with the particle density, leading to the formation of an insulating state even at in?nitesimally small lattice depths. Here we examine the properties of the gas at all lattices depths and, in addition to the static properties, also consider the non-adiabatic dynamics induced by the sudden motion of the lattice potential with a constant speed. Our work provides a continuum counterpart to the work done in discrete lattice models.
关键词： Tonks–Girardeau gas,phase transitions,non-equilibrium dynamics,optical lattices
更新于2025-09-09 09:28:46