Synthetic proustite (Ag3AsS3): A summary of its properties and uses

There is at present great interest in crystals which are suitable for efficient mixing at optical frequencies. Such a crystal should be acentric, have a wide transmission band, have a large non-linear coefficient and permit phase matching. Proustite possesses such properties [1], and this paper summarises the information that has been obtained to date at R R E on these properties and their use in up-converting 10m radiation to the visible, on the available optical quality, on the electro-optic effect, and on electrical conduction in the crystal; some general observations on the type of damage caused to proustite by laser beams are given.     

Photoinduced phase transition in Ag3AsS3 crystals

It is shown that the illumination of samples leads to the appearance of anomalies in the temperature dependences of the propagation velocity of longitudinal ultrasonic waves along the principal crystallographic directions of proustite (Ag₃AsS₃) at T∼150 K. The features discovered are associated with a photoinduced phase transition caused by restructuring of the cation sublattice of proustite. Fiz. Tverd. Tela (St. Petersburg) 41, 702–704 (April 1999)     

The initiating action of continuous heating on structural remodeling in Ag3AsS3 crystals

The effect of continuous heating on the characteristics of phase transformations in proustite (Ag₃AsS₃) is established. It is shown that continuous heating, like continuous cooling, stimulates structural remodeling, in this case reducing the temperature of the known phase transitions. Fiz. Tverd. Tela (St. Petersburg) 40, 2217–2220 (December 1998)     

Far infrared optical properties of proustite (Ag3AsS3)

The infrared reflection and transmission spectra of Ag₃AsS₃ single crystals have been between 20 and 650 cm^-1 at room temperature. Fourteen phonon modes were observable in reflectivity with the dominant restrahlen bands occuring at 360 cm^-1 and 35 cm^-1 for E? c and at 335 cm^-1 and 35 cm^-1 for E⊥ c. These measurements indicate that generation of far infrared radiation by mixing of two laser frequencies using proustite as the down-conversion crystal is not possible.     

Surface resistance measurements at the metal/electrolyte interface of Ag(100) and Ag(111) thin film electrodes

The conductivity of thin film metal electrodes with a thickness of the order of the mean free path of the conduction electrons (50 nm at 300 K) is sensitive to several processes on the metal surface (e.g. adsorption and desorption of ions). We developed epitaxially grown Ag(100)/MgO(100) and Ag(111)/TiO₂(110) electrodes of 20 nm thickness. The change in the surface resistance of Ag(100) thin film electrodes during adsorption of the halide ions Cl⁻, Br⁻ and I⁻ shows the different strengths of specific adsorption. We investigated the phase transition of thiocyanate (SCN⁻) on Ag(100) electrodes by combining the surface resistance method with voltammetric, capacitance and ex-situ XPS measurements. The influence of adsorbed uracil on the resistance of Ag(100) films was demonstrated. The surface resistance is very sensitive to small concentrations of metal cations (e.g. Tl⁺). The surface resistance of Ag(100) and Ag(111) thin film electrodes shows the typical difference in the stripping potential of Tl⁺ of about 100 mV.     

Differential absorption lidar (DIAL) measurements from air and space

The technology and applications of the differential absorption lidar (DIAL) technique have progressed significantly since the first DIAL measurements of Schotland [1], and airborne DIAL measurements of ozone and water vapor are frequently being made in a wide range of field experiments. In addition, plans are underway to develop DIAL systems for use on satellites for continuous global measurements. This paper will highlight the history of airborne lidar and DIAL systems, summarize the major accomplishments of the NASA Langley DIAL program, and discuss specifications and goals for DIAL systems in space. Received: 2 April 1998     

Thermally and optically induced effects on sub-band gap absorption in nanocrystalline CdSe (nc-CdSe) thin films

Nanocrystalline cadmium selenide (nc-CdSe) thin films have been prepared by thermal evaporation using the inert gas condensation (IGC) technique. Transmission electron microscopy (TEM) studies show that the CdSe nanocrystals (NCs) are spherical in shape. Constant photocurrent method (CPM) is used to determine the value of absorption coefficient in low absorption region of as-deposited, annealed and light soaked nc-CdSe thin films. Values of optical band gap (E_g) have been determined by using Tauc's relation for as-deposited, annealed and light soaked nc-CdSe thin films from the α values evaluated from reflection and transmission measurements. We have used a derivative procedure to sub-gap absorption spectra in order to get information on the energetic distribution of the occupied density of states below Fermi level. Constants such as optical gap E_g, Urbach edge E_u have been obtained from CPM spectra in as-deposited, annealed and light soaked nc-CdSe thin films. Concentration of defect states has also been calculated in as-deposited, annealed and light soaked nc-CdSe thin films.     

The absorption of Ag on Ge(100)-(2 × 1)

The initial stages of interface formation for Ag deposited onto Ge(100)-(2 × 1) were studied with high-energy electron diffraction and high- resolution photoemission. The surface core-level energies for clean Ge(100)-(2 × 1) were not changed with the deposition of about one monolayer of Ag, indicating that there was no chemical reaction or atomic intermixing. The Ag nucleated at a coverage of about $\text{1}\text{3}$ monolayer and showed three-dimensional growth for higher coverages.     

Absolute OH absorption cross sections (for lidar measurements)

Absorption cross sections are important in quantitative optical measurements of OH. We have used existing experimental data to calculate the effective cross sections for a number of transitions in the A-X system of OH, taking into account such factors as temperature and the spectral shape and width of both the absorption line and the excitation source. Details of the calculations are presented to allow easy extension to other transitions.     

Up-conversion of CO laser lines by difference-frequency mixing in proustite (Ag3AsS3)

Phase-matched cw up-conversion of CO laser radiation has been obtained in proustite (Ag₃AsS₃). The wavelength of the up-converted radiation varied from 0.69 to 0.72 μm. Detailed data on the phase-matching angles are given.     

Two-photon absorption and resonant non-phase-matched second-harmonic generation in CdSe

Exciting a hexagonal CdSe crystal with picosecond Nd: glass laser pulses, two-photon absorption and resonant non-phase-matched second-harmonic generation occur simultaneously. Using different crystal orientations, all components of the secondharmonic susceptibility tensor (non-vanishing components ared ₃₁,d ₃₃ andd ₁₅) and some components of the two-photon absorption susceptibility tensor _ijkl ⁽³⁾ (–_L; _L, _L, –_L) are determined.     

Exciton and phonon spectra of acoustooptic Tl3AsS3 crystals

The λ-modulated exciton reflection spectra of Tl₃AsS₃ crystals are investigated at 8 and 77 K, in which the ground (n=1) and excited (n=2, 3) exciton states are revealed. Taking into account the spatial dispersion, the shapes of λ-modulated reflection spectra of the n=1 line are calculated and the basic parameters of excitons and bands are determined (the translational and reduced masses of excitons and the effective masses of electrons and light and heavy holes). The one-phonon reflection spectra are studied in the region from 50 to 500 cm^?1 in polarizations E ∥ c and E ⊥ c. The shapes of one-phonon reflection spectra are calculated and the parameters of vibrational modes E and A ₂ are determined.     

Enhanced photoluminescence of CdSe quantum dots by the coupling of Ag nanocube and Ag film

The coupling of local surface plasmon(LSP) of nanoparticle and surface plasmon(SP) mode produced by metal film can lead to the enhanced electromagnetic field, which has an important application in enhancing the fluorescence of quantum dots(QDs). Herein, the Ag nanocube and Ag film are used to enhance the fluorescence of CdSe QDs. The enhancement is found to relate to the sizes of the Ag nanocube and the thickness of the Ag film. Moreover, we also present the fluorescence enhancement caused by only SP. The result shows that the coupling between metal nanoparticles and metal film can realize larger field enhancement. Numerical simulation verifies that a nanocube can localize a strong electric field around its corner. All the results indicate that the fluorescence of QDs can be efficiently improved by optimizing the parameters of Ag film and Ag cubes.     

Nonlinear absorption and refraction of light in a colloidal solution of CdSe/ZnS quantum dots upon two-photon resonant excitation

This paper reports on the results of an investigation into the nonlinear transmission of individual ultrashort pulses of a train generated by a mode-locked laser through a colloidal solution of CdSe/ZnS quantum dots in toluene upon two-photon resonant excitation of the fundamental optical transition. The specific features of the nonlinear transmission are explained in terms of the two-photon absorption and self-defocusing processes. Analysis of the experimental results makes it possible to separate the self-defocusing processes that are governed by the inertialess change in the refractive index due to the interaction of high-power optical pulses with bound electrons and those determined by the nonlinear change in the refractive index under the action of two-photon-excited carriers in a quantum dot.     

Cyclic voltammetry and near edge X-ray absorption fine structure spectroscopy at the Ag L3-edge on electrochemical halogenation of Ag layers on Au(111)

One to three layers of Ag grown on a Au(111) electrode were studied by cyclic voltammetry in chloride and bromide solutions and by ex-situ near-edge X-ray absorption fine structure spectroscopy at the Ag L3-edge (Ag L3-NEXAFS). The one and two layers obtained by underpotential deposition exhibited reduced intensity at the absorption edge in the Ag L3-NEXAFS spectra, which suggests the gain of d-electrons in these layers. The cyclic voltammograms and the Ag L3-NEXAFS spectra indicate that the second and third layers of Ag halogenated at positive potentials, whereas the first layer remained in metallic form.     

(CdSe)n(n=1,2)团簇性质及CdSe分子热力学性质的理论计算

用密度泛函B3LYP方法、有效核势(ECP)基组LanL2DZ对(CaSe)n(n=1,2)团簇进行了理论研究,得到(CaSe)n(n=1,2)分子体系可能存在的状态及各电子状态的平衡几何Re、谐振频率、偶极矩和离解能De、不同温度、压力下的热力学函数值;设用总能量中的电子和振动能量近似代表CdSe分子处于固态时的能量,用总熵中的电子和振动熵近似代表CdSe分子处于固态时的熵,进而计算了Cd与Se反应的△Hθ、△Sθ、△G,并由此计算出不同温度的反应平衡常数Kp结果表明:在298～1400K温度范围内,Cd与Se反应的自由能值均为负,且随着温度的升高,△Gθ值负的越多,表明在这个温度范围内反应能自发发生,而且自发趋势随温度的升高逐渐增大;平衡常数逐渐减小,即反应进行程度随温度的升高逐渐减小;CdSe分子材料的导电性随压力增大而增强.     

Multiexciton absorption and multiple exciton generation in CdSe quantum dots

Efficient multiple-exciton generation (MEG) in semiconductor quantum dots has been recently reported. The MEG efficiency has so far been evaluated assuming that the change (bleaching) of the absorption spectrum due to MEG is linearly proportional to the number of excitons N(X). Here, we critically examine this assumption using atomistic pseudopotential calculations for colloidal CdSe nanocrystals. We find that the bleaching of the first absorption peak depends nonlinearly on N(X), due to carrier-carrier interactions. This nonlinearity mandates an upper bound of 1.5 to the value of the normalized bleaching that can be attributed to MEG, significantly smaller than the limit of 2.0 predicted by the linear scaling assumption. Thus, measured values of the normalized bleaching in excess of 1.5 cannot be due entirely to MEG, but must originate in part from other mechanisms.