Transformations of iodine species inside elliptical channels of AlPO4‐11 crystals at low temperature: a Raman study

Raman spectra of iodine species confined in one‐dimensional elliptical channels of AlPO₄‐11 (AEL) crystals have been studied from room temperature down to −196 °C. As temperature decreases, thermal fluctuations of individual iodine molecules confined in AEL channels are slowed down and they prefer to rotate to channel axis direction, which increases the population of iodine molecules along channel axis (i.e., lying molecules and chains). Such temperature‐driven orientation transformation of iodine molecules is found to be reversible upon heating up to room temperature. The experimental observations are in good agreement with our theoretical simulations by molecular dynamics on low density iodine‐filled AEL crystals. We thus provide a new way to modulate the orientation of iodine molecules in nanochannels, which may have implications in low‐temperature‐sensitive nanoscale devices. Copyright © 2015 John Wiley & Sons, Ltd.     

Raman spectroscopy of bromine chains inside the one‐dimensional channels of AlPO4‐5 single crystals

Raman spectroscopy of the one‐dimensional atomic or molecular chains, which are the attractive building blocks of advanced nanoscale materials, is crucial in understanding the physical properties of the one‐dimensional atomic or molecular chains. Here, we introduce the bromine into the one‐dimensional channels of AlPO₄‐5 single crystals through a physical vapor diffusion method. Raman spectroscopy indicates that the confined bromine structures mainly exist as (Br₂)_n chains, individual Br₂ molecules, and a small amount of Br₃⁻ chains inside the channels of AlPO₄‐5 single crystals. Polarized Raman spectra demonstrate that the bromine molecular chains are approximately parallel to the channel direction of AlPO₄‐5 single crystals. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and Raman characterization of mono-sized single-wall carbon nanotubes in one-dimensional channels of AlPO4-5 crystals

Mono-sized single-wall carbon nanotubes were formed in one-dimensional channels of AlPO₄-5 single crystal (AFI) by pyrolysis of tripropylamine (TPA). Raman spectra have been measured for the TPA-AFI crystals thermally processed at different conditions. TPA molecules are carbonized at 400 °C, and carbon nanotubes were formed at 500 °C or above. The radial-breathing mode, which is special for carbon nanotube geometry, was observed. Three Raman-active modes with symmetry A _1g, E _1g, and E _2g were identified by detailed symmetrical analysis for the polarized-Raman spectra. Received: 29 October 1998 / Accepted: 29 March 1999 / Published online: 24 June 1999     

On the synthesis of AlPO4-21 molecular sieve by vapor phase transport method and its phase transformation to AlPO4-15 molecular sieve

An experimental design was applied to the synthesis of AlPO₄-21 molecular sieve (AWO structure) by vapor phase transport (VPT) method, using tetramethylguanidine (TMG) as the template. In this study, the effects of crystallization time, crystallization temperature, phosphor content, template content and water content in the synthesis gel were investigated. The materials obtained were characterized by X-ray diffraction, scanning electron microscopy and fourier transform infrared spectroscopy (FT-IR). Microstructural analysis of the crystal growth in vapor synthetic conditions revealed a revised crystal growth route from zeolite AlPO₄-21 to AlPO₄-15 in the presence of the TMG. Homogenous hexagonal prism AlPO₄-21 crystals with size of 7 × 3 μm were synthesized at a lower temperature (120 °C), which were completely different from the typical tabular parallelogram crystallization microstructure of AlPO₄-21 phase. The crystals were transformed into AlPO₄-21 phase with higher crystallization temperature, longer crystallization time, higher P₂O₅/Al₂O₃ ratio and higher TMG/Al₂O₃ ratio.     

Separation of dichloromethane-nitrogen mixtures by adsorption: experimental and molecular simulation studies

Experimental and grand canonical Monte Carlo simulation results for the separation of a CH²C1² (1.5 mol%)-N₂ binary gas mixture in molecular sieve materials are presented. AlPO₄-5 and MCM-41 molecular sieves have been used as the selective adsorbents because they consist of uniform arrays of uni-dimensional channels of micro and meso length scales, respectively. Adsorption isotherms were measured at 318 K and at pressures between 50 kPa and 130 kPa. Two MCM-41 materials have been used, one with a 33 A pore diameter and the other with a 42 Á pore diameter. For AlPO₄-5 at 110kPa the total amount adsorbed from experiment was found to be independent of equilibration time at 0.0542, 0.0538 and 0.0547 mmol per g AlPO₄-5 for 2, 24 and 48 hours, respectively. However, the selectivity for CH₂C1₂ was found to increase with time from 1.29, to 4.59, to 10.74. For MCM-41 at 110kPa the selectivity for CH₂C1₂ was found to be dependent on pore size. On increasing the pore size from 33 Å to 42 Á the selectivity for CH₂C1₂ increased considerably. Grand canonical Monte Carlo simulations agreed qualitatively with the experimental results, showing a greater selectivity for CH₂C1₂ than for N₂. The simulations indicate that MCM-41 has a lower selectivity for CH₂C1₂ than A1PO₄-5, which contradicts the experimental results. Reasons for these discrepancies are presented and discussed.     

Electrostatic potential and interaction energies of molecular entities occluded in the AlPO4-15 molecular sieve: determination from X-ray charge density analysis

Electrostatic interaction energies of water molecules, hydroxyl and ammonium ions occluded in AlPO₄-15 molecular sieve are estimated from the modeling of the experimental X-ray charge density by numerical integration using a partitioning of the density based on multipolar pseudo-atoms.     

Observation of the Meissner effect in the high-Tc (pressure-) phase of the organic superconductor β-(BEDT-TTF)2I3

It is shown that the recently found superconducting state below 6 K in β-(BEDT-TTF)₂I₃ under a pressure of 1.5 kbar is diamagnetic and exhibits Meissner effects of up to 24 %, indicating that superconductivity is a true volume effect in these crystals. In contrast, no traces of diamagnetism are found in iodine doped α-(BEDT-TTF)₂I₃, for which resistively observed superconducting transitions in the vicinity of 3 to 5 K have also been reported.     

The mechanism of sensitized anti-stokes luminescence in crystals with adsorbed dyes

We have analyzed regular features of sensitization processes of crystals AgCl, AgCl_0.95I_0.05, and Zn_0.6Cd_0.4S to processes of a low-threshold (10^?3–10^?4 W/cm²) two-quantum excitation of anti-Stokes luminescence by adsorbed molecules and by J and H aggregates of dyes of different classes. The excitation centers of this luminescence are complex and consist of dye molecules and few-atom silver clusters adsorbed nearby. Luminescence-excitation processes involve stages of photoexcitation of adsorbed dye molecules; resonance transfer of electronic excitation energy to adsorbed atoms and few-atom silver clusters, levels of which lie near the middle of the band gap; and their subsequent photoionization.     

Multiphoton ionization of iodine atoms and CF<Subscript> 3</Subscript>I molecules by XeCl laser radiation

We report about effective ionization of iodine atoms and CF₃I molecules under the action of intense XeCl laser radiation (308 nm). The only ion fragment resulting from the irradiation of the CF₃I molecules is the I⁺ ion. We have studied the influence of the intensity, spectral composition, and polarization of the laser radiation used on the intensity of the ion signal and the shape of its time-of-flight peak. Based on the analysis of the results obtained, we have suggested the mechanism of this effect. The conclusion drawn is that the ionization of the iodine atoms by the ordinary XeCl laser with a nonselective cavity results from a three- (2 + 1)-photon REMPI process. This process is in turn due to the presence of accidental two-photon resonances between various spectral components of the laser radiation and the corresponding intermediate excited states of the iodine atom. The probability of ionization of the atoms from their ground state I(²P_3/2) by the radiation of the ordinary XeCl laser is more than two orders of magnitude higher than the probability of their ionization from the metastable state I^*(²P_1/2). The ionization of the CF₃I molecules by the XeCl laser radiation occurs as a result of a four-photon process involving the preliminary one-photon dissociation of these molecules and the subsequent (2 + 1)-photon REMPI of the resultant neutral iodine atoms.     

Identification of I3 − and I5 − clusters in irradiated ki by X-ray photoelectron,Raman and optical absorption spectroscopies

Abstract

Raman and XPS measurements have been performed on KI crystals irradiated near 200 K. The Raman studies show I₃ ^? and I_n ^? (n = 5, 7,—) clusters which anneal together with F- and V- centres at 338 K. A small development of (I₂)_n aggregates occurs during the anneal; these decay near 378 K and are responsible for a broad and weak residual V-band. The I 3d _5/2 XPS peak has been fitted to reveal the presence of 3 components after low energy argon- ion bombardment. These are identified as due to normal lattice iodine, I₃ ^? and 1₅ ^? whose behaviour is consistent with the Raman work.     

Excited state absorption,energy levels,and thermal conductivity of Er<Superscript>3+</Superscript>:YAB

Polarized excited state absorption spectra of Er, Yb:YAB are reported. The Stark levels of the ⁴I_15/2, ⁴I_13/2, and ⁴I_11/2 multiplets of Er³⁺ have been derived from the measured low-temperature absorption and fluorescence spectra. The stimulated emission spectra have been calculated using the reciprocity method, and the radiative lifetime of the erbium ⁴I_13/2 level has been determined indicating high nonradiative decay rates. The thermal conductivity of Er-Yb-codoped YAB crystals has been measured.     

Synthesis and laser patterning of Bi-doped Y3Fe5O12 crystals in germanosilicate glasses

New germanosilicate glasses giving the crystallization of yttrium iron garnet Y₃Fe₅O₁₂ (YIG) and Bi-doped YIG, 23Na₂O-xBi₂O₃-(12−x)Y₂O₃-25Fe₂O₃-20SiO₂-20GeO₂ (mol%), are developed, and the laser-induced crystallization technique is applied to the glasses to pattern YIG and Bi-doped YIG crystals on the glass surface. It is clarified from the Mössbauer effect measurements that iron ions in the glasses are present mainly as Fe³⁺. It is suggested from the X-ray diffraction analyses and magnetization measurements that Si⁴⁺ ions are incorporated into YIG crystals formed in the crystallization of glasses. The irradiations (laser power: 32-60 mW and laser scanning speed: 7 μm/s) of continuous wave Yb:YVO₄ fiber laser (wavelength: 1080 nm) are found to induce YIG and Bi-doped YIG crystals, indicating that Fe³⁺ ions in the glasses act as suitable transition metal ions for the laser-induced crystallization. It is suggested that YIG and Bi-doped YIG crystals in the laser irradiated part might orient. The present study will be a first step for the patterning of magnetic crystals containing iron ions in glasses.     

Influence of parameters of gas medium on the fluorescence of iodine molecules 129I2, 127I129I and 127I2 excited by semiconductor laser radiation

Calculated and experimental results of studies of the influence of vapor temperature of iodine molecules (¹²⁹I₂, ¹²⁷I¹²⁹I, and ¹²⁷I₂) and pressure of the analyzed medium on the intensity of fluorescence of the molecules excited by semiconductor laser radiation in the red spectrum region are reported. It is demonstrated that depending on the wavelength of laser radiation there exist different ranges of temperatures and pressure values at which the fluorescence intensities of each of the indicated iodine molecules reach their maximum values.     

Influence of lithium phosphate concentration and temperature on the electrical conduction of (76V2O5-24P2O5)1−X (Li3PO4)X glasses

Characterization of the (76V₂O₅-24P₂O₅)_1−X (Li₃PO₅)_X, where X=0.0,0.01,0.02,0.10 and 0.15, glass has been done using X-ray diffraction and differential thermal analysis (DTA). The dc conductivity of the glass samples was studied over a temperature range from 300 to 593 K. The temperature dependence of dc conductivity shows two regions. One at relatively high temperature range, above θ_D/2, and the other at relatively low temperature range, below θ_D/2. The I-V characteristics of the glasses have been studied as a function of both temperature and Li₃PO₄ content. The I-V characteristics exhibits threshold switching with differential negative resistance. It's found that both the threshold voltage (V_th) and threshold current (I_th) are dependent on the temperature and lithium phosphate concentration.     

Photoinduced color centers creation in superionic crystals RbAg 4 I 5

Abstract

A new phenomenon of a reversible photoinduced coloration caused by light irradiation is discovered and investigated in superionic RbAg ₄ I ₅ crystals. The reversible photoinduced absorption is found to be a result of irradiation by light with wavelengths in the region from 420 nm to 450 nm. The proposed mechanism of the discovered effect is associated with ambipolar diffusion of screened by mobile ions optically excited electronic carriers. The processes of color centers creation in superionic crystals RbAg ₄ I ₅ due to additive coloring in iodine vapours, ionic implantation and γ-ray irradiation are considered.     

Experimental preparation of entangled Bell’s vacuum-single exciton and vacuum-biexciton states for pair centers of neodymium ions in a crystal

The process of low temperature laser excitation of neodymium ion M pair centers in CaF₂ crystals at the ⁴I_9/2-⁴G_5/2 optical transition is analyzed. It is shown that maximally entangled Bell’s vacuum-single exciton and vacuum-biexciton states are experimentally prepared when irradiating these crystals by nanosecond laser pulses.     

Structural manipulation of ultrathin organic films on metal surfaces: the case of decane thiol/Au(111)

3 (CH₂)₉]SH) have been adsorbed on Au(111) single crystals both via vacuum deposition and from an ethanolic solution. The epitaxial structure of the ultrathin organic films has been identified at room temperature via low-energy electron diffraction to be c(4×2)R30° for the solution grown film and rectangular c(23×) for the vacuum deposited film. These structures correspond to molecules adsorbed on the surface with their carbon chains flat on the surface (vacuum deposited) and nearly perpendicular (solution grown). It is demonstrated that this orientation can be changed reversibly in vacuum via either annealing the films or exposing them to additional gas. Received: 7 February 1997/Accepted: 27 May 1997     

Precise frequency measurements of lines in the near infrared by Rb reference lines

Frequency measurements of 16 lines of I₂ in the near infrared have been performed using different Rb frequency references: diode lasers stabilised to the Rb D1 line at 377 THz, to the Rb D2 line at 384 THz and to the 5 s -5 d two photon transition at 385 THz. The relative uncertainties of the measurements of are limited by the frequency stability of the laser source locked to I₂ in the case of the Rb D2 and two photon transition or by the accuracy of the Rb D1 line. The internal consistency of calibrations of iodine lines is shown to be better than by measurements of the difference frequencies of calibrated iodine lines using four-wave mixing in laser diodes. Received 12 July 1999 and Received in final form 12 December 1999     

Dissociative multiple photoionization of Br2, IBr,and I2 in the VUV and X-ray regions: a comparative study of the inner-shell processes involving Br(3d,3p,3s) and I(4d,4p,4s,3d,3p)

Dissociative multiple photoionization of the bromine, the iodine monobromide, and the iodine molecules in the Br(3d,3p,3s) and I(4d,4p,4s,3d,3p) inner-shell regions has been studied by using time-of-flight (TOF) mass spectrometry coupled to synchrotron radiation in the ranges of 90∼978 eV for Br₂, 60∼133 eV for IBr, and 86∼998 eV for I₂. Total photoion and photoion–photoion coincidence (PIPICO) yields have been recorded as functions of the photon energy. Here, giant shape resonances have been observed beyond the thresholds of the inner-shells owing to the Br(3d¹⁰)→Br(3d⁹ϵf), I(4d¹⁰)→I(4d⁹ϵf), and I(3d¹⁰)→I(3d⁹ϵf) transitions. The dissociation processes of the multiply charged parent ions have also been evaluated from variations of photoelectron–photoion coincidence (PEPICO) and PIPICO spectra with the photon energy. From each Br(3p_3/2) (189.9 eV) and I(4p_3/2) threshold (129.9 eV), quintuple ionization of the molecules begins to play important roles in the photoionization, subsequently yielding ion pairs of X³⁺–X²⁺ (X=Br, I). From the I(3d_5/2) threshold (627.3 eV), loss of six electrons from iodine molecule additionally begins to play a minor role in the multiple photoionization, giving rise to the formation of ion pairs of either I³⁺–I³⁺ or I⁴⁺–I²⁺. A direct comparison of the strengths and the ranges of the I(4d) and Br(3d) giant resonances was successfully made from dissociative photoionization of IBr. Over the entire energy range examined, 60<E<133 eV, biased charge spread relevant to the specific core-hole states of IBr is observed, presumably reflecting the fact that charge localizes mostly in the excited atoms, which can be accounted for mainly by a two step decay via a fast dissociation followed by autoionization upon the VUV absorption.     

Synthesis, characterization and application of iodine modified titanium dioxide in phototcatalytical reactions under visible light irradiation

Iodine doped titanium dioxide has been successfully prepared by simple hydrolysis of tetrabutyl titanate in the presence of iodic acid. The adopted method allowed for the production of spherical iodine doped titaniun dioxide nanoparticles with varied amount of iodine content. Analysis by X-ray diffraction, Raman, transmission electron microscopy as well as UV-vis DRS revealed that titanium dioxide nanostructures were doped with iodine which existed in two different valence states I⁵⁺ and I⁻. The iodine in the form of I⁵⁺ is believed to have doped into the lattice whereas I⁻ was well dispersed on the surface of TiO₂ probably as iodine adducts hence rendering it to be highly absorbing in visible light region. The I-TiO₂ exhibited improved photocatalytic activity toward degradation of acid orange 7 (AO7), methyl orange (MO) and 2,4-dichlorophenol (2,4-DCP) under visible light over the pristine TiO₂ prepared by the same method. High catalytic properties are attributed to iodine doping which led to high specific surface area, absorption in visible region as well as alleviation of charge carrier recombination. The most probable route undertaken in the degradation of AO7 is through indirect oxidation by the hydroxyl radicals.