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1.
We show the influence of species present in precursor solution during formation of lead halide perovskite materials on the structural defects of the films. The coordination of lead by competing solvent molecules and iodide ions dictate the type of complexes present in the films. Depending on the processing conditions all PbIS5+, PbI2S4, PbI3S3?, PbI4S22?, PbI5S23?, PbI64?and 1D (Pb2I4)n chains are observed by absorption measurements. Different parameters are studied such as polarity of the solvent, concentration of iodide ions, concentration of solvent molecules and temperature. It is concluded that strongly coordinating solvents will preferentially form species with a low number of iodide ions and less coordinative solvents generate high concentration of PbI6?. We furthermore propose that all these plumbate ions may act as structural defects determining electronic properties of the photovoltaic films.  相似文献   

2.
Interaction of bromine ions absorbed by water cluster with adsorbed oxygen and ozone molecules has been investigated by the molecular dynamics method. It was shown that the part of O2 molecules was removed from the system by evaporating Br ions, while all O3 molecules and Br ions were kept in the system during 25 ps. The increase the concentration of the Br ions in the clusters resulted in a reduction of the absorption intensity and emission in IR spectra at the presence of oxygen, whereas the absorption intensity in the appropriate IR spectra of ozone-containing systems increased with the growth of a number of the Br ions. Raman spectra of oxygen-containing systems were poorly sensitive to the concentration of the Br ions but the absorption intensity of Raman spectra for systems with ozone considerably decreased with the growth of a number of bromine ions.  相似文献   

3.
The formation of clusters CH2(COO)(COOAg3 +) (absorption bands at 280 and 460 nm) by the reduction of silver ions in the presence of malonate ions in an aqueous solution was studied by pulse radiolysis. The disappearance of the clusters affords colloidal silver. The mechanism of silver nucleation was discussed, and the rate constants of some reactions were determined. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1819–1822, August, 2005.  相似文献   

4.
In this work, we present a detailed investigation of the optical properties of hybrid perovskite building blocks, [PbI2+n]n−, that form in solutions of CH3NH3PbI3 and PbI2. The absorbance, photoluminescence (PL) and photoluminescence excitation (PLE) spectra of CH3NH3PbI3 and PbI2 solutions were measured in various solvents and a broad concentration range. Both CH3NH3PbI3 and PbI2 solutions exhibit absorption features attributed to [PbI3]1− and [PbI4]2− complexes. Therefore, we propose a new mechanism for the formation of polymeric polyiodide plumbates in solutions of pristine PbI2. For the first time, we show that the [PbI2+n]n− species in both solutions of CH3NH3PbI3 and PbI2 exhibit a photoluminescence peak at about 760 nm. Our findings prove that the spectroscopic properties of both CH3NH3PbI3 and PbI2 solutions are dominated by coordination complexes between Pb2+ and I. Finally, the impact of these complexes on the properties of solid-state perovskite semiconductors is discussed in terms of defect formation and defect tolerance.  相似文献   

5.
Nanostructured Ag films composed of nanoparticles and nanorods can be formed by the ultrasonication of ethanol solutions containing Ag2O particles. The present work examined the formation process of these films from ethanol solutions by two different agitation methods, including ultrasonication and mechanical stirring. The mass-transfer process from Ag2O particles to ethanol solvent is accelerated by the mechanical effects of ultrasound. Ag+ ions and intermediately reduced Ag clusters were released into the ethanol. These Ag+ ions and Ag clusters provide absorption bands at 210, 275 and 300 nm in UV-vis spectra. These bands were assigned to the absorption of Ag+, Ag 4 2+ and Agn (n?≈?3). The Agn clusters that readily grow to become Ag nanoparticles were formed due to the surface reaction of Ag2O particles with ethanol under ultrasonication. The reactions of Ag+ ions in ethanol to form Ag nanomaterials (through the formation of Ag 4 2+ clusters) were also accelerated by ultrasonication.  相似文献   

6.
Spectral characteristics of (H2O)n, (O2)m(H2O)n, and (O)i(H2O)n cluster systems, where m≤2, i≤4, and 10 ≤ n ≤ 50, are studied with the molecular dynamics method using a flexible molecule model. The IR absorption spectra are changed substantially as a result of O2 molecule dissociation, and in the presence of atomic oxygen in the clusters, the spectra are characterized by a deep minimum at 520 cm?1. The absorption of oxygen causes a marked reduction in reflection coefficient R of monochromatic IR radiation. The number of peaks in the R(ω) spectra decreases to two in the case of molecular oxygen absorption and is no larger than four in the case of atomic oxygen absorption. The absorption of atomic oxygen by the clusters is also accompanied by a significant increase in the dissipation of energy accumulated by the clusters. This effect weakens when molecular oxygen is absorbed. An increase in atomic oxygen concentration in the clusters renders their radiation harder.  相似文献   

7.
Three different commonly used infrared photodissociation (IRPD) spectroscopy acquisition and analysis methods are described, and results from these methods are compared using the same dataset for an extensively hydrated metal cation, La3+(H2O)36. Using the first-order laser-induced photodissociation rate constant as an IRPD intensity has several advantages over photodissociation yield and depletion/appearance methods in that intensities can be more directly compared with calculated infrared absorption spectra, and the intensities can be readily corrected for changes in laser power or irradiation times used for optimum data acquisition at each frequency. Extending IRPD spectroscopy to large clusters can be complicated when blackbody infrared radiative dissociation competes strongly with laser-induced photodissociation. A new method to obtain IRPD spectra of single precursor ions or ensembles of precursor ions that is nearly equivalent to the photodissociation rate constant method for single precursor ions is demonstrated. The ensemble IRPD spectra represent the “average” structure of clusters of a given size range, and this method has the advantage that spectra with improved signal-to-noise ratios can be obtained with no increase in data acquisition time. Results using this new method for a precursor ensemble consisting of La3+(H2O)35–37 are compared with results for La3+(H2O)36.  相似文献   

8.
Organic–inorganic hybrid material of formula (C4H3SC2H4NH3)2[PbI4] was synthesized and studied by X-ray diffraction, Infrared absorption, Raman scattering, UV–Visible absorption and photoluminescence measurements. The molecule crystallizes as an organic–inorganic two-dimensional (2D) structure built up from infinite PbI6 octahedra surrounded by organic cations. Such a structure may be regarded as quantum wells system in which the inorganic layers act as semiconductor wells and the organic cations act as insulator barriers. Room temperature IR and Raman spectra were recorded in the 520–3500 and 10–3500 cm−1 frequency range, respectively. Optical absorption measurements performed on thin films of (C4H3SC2H4NH3)2[PbI4] revealed three distinct bands at 2.4, 2.66 and 3.25 eV. We also report DFT calculations of the electric dipole moments (μ), polarizability (α), the static first hyperpolarizability (β) and HOMO–LUMO analysis of the title compound investigated by GAUSSIAN 09 package. The calculated static first Hyperpolarizability is equal to 11.46 × 10−31 esu.  相似文献   

9.
We describe here molecular dynamics computer simulations performed to study the solvation of ions (Cl? and Na+) in water clusters. Our simulations show that the calculated structure and dynamics of the clusters is very sensitive to the potential model which is used to describe the interactions. From the comparison with thermodynamic data and data from the photoelectron spectra we conclude that in Cl?(H2O)n (n≤20) clusters the ion is located on the surface of the cluster.  相似文献   

10.
Colloidal copper has been obtained by -irradiation of aqueous solutions of copper (II) perchlorate in the presence of alcohol and polyethyleneimine (PEI). The sols are spherical particles about 4 nm in diameter, which are quickly oxidized by oxygen or other oxidants. When CuII is not entirely incorporated into the complex with PEI, disproportionation of CuI aqua complexes formed affords the metal, along with Cu2O. Reduction of the PEI complex of CuI by hydrated electrons gives only colloidal copper. The copper ions can be reduced on the surface of silver sols. Optical parameters of the resulting bimetallic particles have been studied. The presence of copper ions leads to broadening of the absorption band associated with the silver sols and shifts it to the UV region, which is due to the transfer of electrons from copper to silver. Three copper monolayers are enough to cause plasmon absorption of colloidal copper.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 25–30, January, 1994.  相似文献   

11.
Interfacial properties between perovskite layers and metal electrodes play a crucial role in the device performance and the long-term stability of perovskite solar cells. Here, we report a comprehensive study of the interfacial degradation and ion migration at the interface between CH3NH3PbI3 perovskite layer and Ag electrode. Using in situ photoemission spectroscopy measurements, we found that the Ag electrode could induce the degradation of perovskite layers, leading to the formation of PbI2 and AgI species and the reduction of Pb2+ ions to metallic Pb species at the interface. The unconventional enhancement of the intensities of I 3d spectra provides direct experimental evidences for the migration of iodide ions from CH3NH3PbI3 subsurface to Ag electrode. Moreover, the contact of Ag electrode and perovskite layers induces an interfacial dipole of 0.3 eV at CH3NH3PbI3/Ag interfaces, which may further facilitate iodide ion di usion, resulting in the decomposition of perovskite layers and the corrosion of Ag electrode.  相似文献   

12.
《Tetrahedron letters》2014,55(51):7094-7098
A new thiacalix[4]arene based fluorescent chemosensor thiacalix[4]arene-N-(quinolin-8-yl)acetamide (TCAN8QA) has been synthesized. TCAN8QA has been found to exhibit highly selective behavior for F ions among all other anions, that is, Cl, Br, I, PO4−3, OH, H2PO4, and CH3COO in the absorption spectra as well as in the emission spectra. Red shift and quenching in emission spectra constituting the signature for fluoride detection are due to photoinduced charge transfer (PCT) which can be attributed to deprotonation of acidic NH proton in the presence of fluoride ions.  相似文献   

13.
An experimental and theoretical investigation is reported to analyze the relation between the structural and absorption properties of CH3NH3PbI3 in the tetragonal phase. More than 3000 geometry optimizations were performed to reveal the structural disorder and identify structures with the lowest energies. The electronic structure calculations provide an averaged band gap of 1.674 eV, which is in excellent agreement with the experimental value of about 1.6 eV. The simulations of the absorption spectrum for three representative structures with lowest energy reproduced the absorption shoulders observed in the experimental spectra. These shoulders are assigned to excitations having similar orbital characters and involving transitions between hybridized 6s(Pb)/5p(I) orbitals and 6p(Pb) orbitals. The geometries of the three structures were analyzed and the effects of the inorganic frame and the CH3NH3+ cations on the absorption properties were estimated. It was found that both changes in the inorganic frame and the CH3NH3+ cations orientations impact the absorption spectra, by modifying the transitions energies and intensities. This highlights the role of CH3NH3+ cation in influencing the absorption properties of CH3NH3PbI3 and demonstrates that CH3NH3+ cation is one of the key elements explaining the broad and nearly constant absorption spectrum in the visible range.  相似文献   

14.
Optical absorption spectra of aqueous solutions of the giant cluster Pd561Phen60(OAc)180 (1) were studied in air and after treatment with H2. The results obtained were compared with the corresponding data for 2—4-nm nanoparticles of colloidal palladium prepared by the radiochemical and chemical reduction of the PdII complexes in aqueous solutions. The optical spectra of cluster 1 and nanoparticles of colloidal palladium are of the same nature and are caused by the light absorption by free electrons in the metal.  相似文献   

15.
Using the molecular dynamics method, the joint absorption of oxygen and nitrate ions by water clusters is studied in terms of the polarizable model of flexible molecules. Significant fluctuations are observed in the number of hydrogen bonds in the clusters during the addition of NO3 ions to water-oxygen aggregates. Dielectric permittivity noticeably changes upon the addition of O2 molecules to water clusters and nitrate ions to oxygen-containing water clusters. After the absorption of oxygen molecules and nitrate ions, water clusters markedly lose the ability to IR absorption. The Raman spectrum of a medium formed from disperse aqueous system, oxygen, and nitrate ions displays a greater number of bands than the spectrum of a system of pure water clusters.  相似文献   

16.
We report the syntheses, crystal structure, and magnetic properties of a series of distorted K2NiF4-type oxides Ln2Ca2MnNiO8 (Ln=Pr, Nd, Sm, and Gd) in which Ln/Ca and Mn/Ni atoms randomly occupy the K and Ni sites respectively. The Ln=La compound does not form. These compounds show systematic distortions from the ideal tetragonal K2NiF4 structure (space group I4/mmm) to an orthorhombic structure (space group Pccn) with buckled MO2 (M=Mn/Ni) layers. The degree of distortion is increased as the size of Ln decreases. Based on the magnetic data and X-ray absorption near edge spectra, we assigned MnIV and NiII. The Curie–Weiss plots of the high temperature magnetic data suggest strong ferromagnetic interactions probably due to MnIV–O–NiII linkages, implying local ordering of Mn/Ni ions to form ferromangnetic clusters in the MO2 layers. At low temperatures below 110–130 K, these compounds show antiferromagnetic behaviors because of MnIV–O–MnIV and/or NiII–O–NiII contacts between the ferromagnetic clusters. The Ln=Pr and Nd compounds show additional antiferromagnetic signals that we attribute to the interlayer interactions between the clusters mediated by the Pr3+ and Nd3+ ions in the interlayer spaces. The present compounds show many parallels with the previously reported Ln2Sr2MnNiO8 compounds.  相似文献   

17.
The growth of ZnO clusters supported by ZnO-bilayers on Ag(111) and the interaction of these oxide nanostructures with water have been studied by a multi-technique approach combining temperature-dependent infrared reflection absorption spectroscopy (IRRAS), grazing-emission X-ray photoelectron spectroscopy, and density functional theory calculations. Our results reveal that the ZnO bilayers exhibiting graphite-like structure are chemically inactive for water dissociation, whereas small ZnO clusters formed on top of these well-defined, yet chemically passive supports show extremely high reactivity - water is dissociated without an apparent activation barrier. Systematic isotopic substitution experiments using H216O/D216O/D218O allow identification of various types of acidic hydroxyl groups. We demonstrate that a reliable characterization of these OH-species is possible via co-adsorption of CO, which leads to a red shift of the OD frequency due to the weak interaction via hydrogen bonding. The theoretical results provide atomic-level insight into the surface structure and chemical activity of the supported ZnO clusters and allow identification of the presence of under-coordinated Zn and O atoms at the edges and corners of the ZnO clusters as the active sites for H2O dissociation.  相似文献   

18.
An electron paramagnetic resonance (EPR) study of FeNbO4 powder samples in monoclinic phase (wolframite-type) at X-band (8.8–9.8 GHz), in the 90–300 K temperature range, is presented. For all the temperatures, the EPR spectrum shows a single line associated with Fe3+ ions. Changes in the lineshape of the EPR spectrum, which can be attributed to Fe2+ ions, are detected at low temperatures. This behavior can be ascribed to a strong magnetic dipolar interaction between Fe2+ and Fe3+ ions. The non-resonant microwave absorption techniques: magnetically-modulated microwave absorption spectroscopy (MAMMAS) and low-field microwave absorption spectroscopy (LFMAS), were used for a further knowledge on this material. MAMMAS response suggests also the presence of Fe2+ ions, that originates a change in microwave absorption regime for T < Tp (=140 K), associated with the presence of short-range magnetic correlations. LFMAS spectra showed a linear behavior with positive slope and non-hysteretic traces. The profiles obtained by plotting the slope vs. temperature of the LFMAS line are similar to those detected by the MAMMAS technique, confirming that both types of measurement show the same processes of absorption.  相似文献   

19.
The interaction of uranium(VI) with carbonate ions was studied with absorption spectroscopy and time-resolved laser-induced fluorescence spectroscopy due to the importance of these complexes in environmental relevant waters. In the pH range from 2 to 11 the influence of the temperature on the spectra was studied to check changes in the abundances of several binding forms. It was found that several binding forms are predominant at different temperatures and pH values. This observation can be explained by speciation changes due to the dependence of chemical equilibria on the temperature. Furthermore photoluminescence spectra of aqueous solutions of uranyl carbonate complexes were observed at ambient temperatures for the first time and single component absorption spectra of the uranyl carbonate complexes UO2(CO3)3 4− and UO2(CO3)2 2− were derived.  相似文献   

20.
The icosahedral [M@Pb12]3− (M=Co( 1 ), Rh( 2 ), Ir( 3 )) cluster ions were prepared from K4Pb9 and Co(dppe)Cl2 (dppe=1,2-bis(diphenylphosphino)ethane)/[Rh(PPh3)3Cl]/[Ir(cod)Cl]2 (cod=1,5-cyclooctadiene), respectively, in the presence of 18-crown-6/ 2,2,2-cryptand in ethylenediamine/toluene solvent mixtures. The [K(2,2,2-cryptand)]+ salt of 1 and the [K(18-crown-6)]+ salt of 3 were characterized via X-ray crystallography; the ions 1 and 3 are isostructural and isoelectronic to the [Rh@Pb12]3− ( 2 ) ion as well as to the group 10 clusters [M′@Pb12]2− (M′=Ni, Pd, Pt). The ions are all 26-electron clusters with near perfect icosahedral Ih point symmetry. Clusters 1 – 3 show record downfield 207Pb NMR chemical shifts due to σ-aromaticity of the cluster framework. Calculated and observed 207Pb NMR chemical shifts and 207Pb–xM J-couplings (xM=59Co, 103Rh, 193Ir) are in excellent agreement and DFT analysis shows that the variations of 207Pb NMR chemical shifts for the [M@Pb12]2, 3− ions (M=Co, Rh, Ir, Ni, Pd, Pt) are mainly governed by the perpendicularly oriented σ11 component of the chemical shift anisotropy tensor. The laser desorption ionization time-of-flight (LDI-TOF) mass spectra contain the molecular ions as well as several new gas phase clusters derived from the parents. The DFT-minimized structures of these ions are described.  相似文献   

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