Alkali Halide Matrices Research Articles

A Method for Polarizing More Number of Impurity-Vacancy Dipoles

Free rotating impurity-vacancy (IV) dipoles in an alkali halide matrix are polarized to the extent of 1/3 of the total number of IV dipoles. An experimental procedure is suggested in this article which will help in the polarization of IV dipoles to the extent of 2/3 of the total number of IV dipoles. In the suggested experimental procedure, the electric field will be applied at first in one direction and then will be applied in succession in opposite direction. Ionic thermocurrent technique is employed to ascertain the increase in polarization of IV dipoles.

Energy dispersion in graphene and carbon nanotubes and molecular encapsulation in nanotubes

Density-functional calculations of electronic and vibrational dispersion energies for pristine graphite monolayer graphene and single-walled carbon nanotubes SWCNTs are presented. Optimized parameters for nonlocal norm-preserving pseudopotentials which replace the potential field due to core electrons are given. Comparison with observations, where available, is made. The effect of encapsulation of carbon nanotubes with an alkali-halide matrix is numerically investigated. The electronic band structure of encapsulated SWCNT is noticeably modified, as is its charge density, and hence its optical properties.

Fractal characteristics of metal clusters self‐assembled in alkali halide matrices

Metal nanoclusters of Ag and Au were obtained in alkali halide crystals (NaCl, KBr and KCl). The fractal character of the structures is proved by the fractal dimensions calculated using a home made computer program. The self aggregation of the metallic structures is governed in both cases (Ag and Au) by the DLA mechanism. This is proved by the values of the fractal dimension calculated using two methods, sandbox and box-counting, which are between 1.7 and 1.8 for Ag and for Au between 1.7 and 1.9. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Infrared spectra of amino acid zwitterions isolated in alkali halide matrices

A new spray sampling method (DSD) exploited in the measurement of infrared absorption of amino acids and dipeptides has resulted in a third category of spectra. They display qualitative similarities to the resolved bands obtained in the vapor and low-temperature inert-gas isolated matrix, and on the other hand have some common vibrational frequencies with the solution and alkali halide pressed pellet spectra. Comparisons of group frequencies obtained by the DSD and pellet methods, and presented for a number of amino acids and dipeptides, are informative of structural differences in the molecules obtained by the two methods. As well, results are presented for the measured and predicted dependence on the alkali halide matrix. It is argued that the sum of evidence presented supports the conclusion that zwitterions isolated as monomers are produced by the DSD sampling method. The method is not exclusive to the amino acids. Other applications include purine and water.

Spectra of surface-enhanced Raman scattering of nanocluster NaXe

The integrated ultraviolet (UV)-micro-laser-matrix can be expected, if the novel nanomaterial with a matrix distribution can emit UV radiation and easily inverses the population between its ground and excited states. Solid NaXe nanoclusters should belong to such a nanomaterial. Metallic Na colloids of nanometer size have been formed as the results of the aggregations of F centers in heavily irradiated NaCl [1]. It has been indicated by the measurements of transmission electron microscopy (TEM) that alkali atoms, including Na and K, in alkali metal colloids retain their original face centered cubic (fcc) positions within the alkali halide matrix and that their lattice parameters are not far different from their host matrix [2]. It has been also evidenced by TEM and selected-area electron diffraction experiments that noblegas ions implanted into metals and magnesium oxide can be trapped and solid noble-gas inclusion can be formed [3]. Their positions have been found to be fccs in fcc matrix [3]. It has been also demonstrated by our former experiments [4, 5] that the novel solid NaXe can be prepared under the appropriate conditions of xenon ion implantation into NaCl samples and a strong 355 nmUV-radiation emission can be observed. In this paper, the surface-enhanced Raman scattering (SERS) spectra of nanocluster NaXe in NaCl are measured at room temperature and their characteristics are discussed. In the experiment, pure NaCl powder, in which the grain diameters are smaller than 53 µm, is pressed to disks as samples. Xenon ions are implanted at 10 −6 Torr by using an accelerating voltage of 200 kV. The xenon ion flux is 5×10 17 ions/cm 2 . Under this implantation condition, solid NaXe nanoclusters with blue color are formed through the interaction between solid Xe and metallic Na colloids in xenon-ion–implanted NaCl samples. The sizes of solid NaXe nanoclusters are measured to be within 80 nm by scanning electron microscopy (Hitachi S-3500N). The Raman-scattering is often enhanced by the colloids formed on the surface of the sample. This process is called SERS [6]. These SERS spectra can provide information about the nature and geometry of the colloids in samples. Therefore, low-frequency Raman-scattering spectra are used to study the colloidal structure in our ∗ Author to whom all correspondence should be addressed.

The FT-IR spectra of glycine and glycylglycine zwitterions isolated in alkali halide matrices

The infrared absorption spectra of glycine and the dipeptide glycylglycine have been measured using a novel spray-sampling technique which leads to better resolved spectra than the traditional crystal and solution methods. Spectra were recorded for a number of different alkali halide matrices. Theoretical predictions of the spectra have been undertaken using the self-consistent reaction field Onsager continuum model, without the inclusion of specific solute solvent interactions. Good agreement has been achieved between measured and predicted structures and spectra. For the glycine zwitterion in alkali halide matrices, the measured spectra suggest a trans structure about the NC bond, while for the dipeptide the conformation about the peptide bond is trans as in the crystal. The DSD spectra showed little dependence on the alkali halide matrix used to isolate the amino acid zwitterions in support of the theoretical approach adopted.

Effect of Hydration on Band Intensities in Diffuse Infrared Spectra of Samples in Alkali Halide Matrices

Effect of Hydration on Band Intensities in Diffuse Infrared Spectra of Samples in Alkali Halide Matrices

Optical responses of alkali-halide matrix (NaCl)-doped silver

In this work, we investigated the optical properties and the evolution of AgCl semiconductor aggregates dispersed in an ionic crystalline matrix, NaCl. These aggregates were obtained by doping the NaCl matrix with a silver powder (Ag). Microcrystals of AgCl of various sizes were consequently obtained with a mean size of 30Å. A thermal annealing, whose principal effect is the variation of crystallite sizes, was then carried out. The study was undertaken in a systematic way by PL, CL measurements and X-ray diffraction (XRD). PL spectrum exhibits a response leading to the formation of AgCl aggregates within NaCl host confirmed by DRX patterns. Also photoluminescence showed the presence of the silver chloride aggregates and their photosensitivity was revealed by the formation of silver clusters.

Optical responses of alkali-halide matrix (NaCl)-doped silver

In this work, we investigated the optical properties and the evolution of AgCl semiconductor aggregates dispersed in an ionic crystalline matrix, NaCl. These aggregates were obtained by doping the NaCl matrix with a silver powder (Ag). Microcrystals of AgCl of various sizes were consequently obtained with a mean size of 30 A ̊ . A thermal annealing, whose principal effect is the variation of crystallite sizes, was then carried out. The study was undertaken in a systematic way by PL, CL measurements and X-ray diffraction (XRD). PL spectrum exhibits a response leading to the formation of AgCl aggregates within NaCl host confirmed by DRX patterns. Also photoluminescence showed the presence of the silver chloride aggregates and their photosensitivity was revealed by the formation of silver clusters.

Magnetic resonance in micro- and nanostructures

GaAs/AlAs and GaAs/AlGaAs quantum wells and superlattices were grown by molecularbeam epitaxy and self-organized oriented silver halide micro- and nanocrystals were embedded in crystalline alkali halide matrix. We report the results of the application of optically detected magnetic resonance (ODMR) and level anticrossing (LAC) spectroscopy for the investigations of these two classes of nanostructures. ODMR and LAC spectroscopy are shown to be very suitable for obtaining important physical parameters of low-dimensional systems and for a local diagnostics of nanostructures.

Infrared absorption of lanthanum manganites

Phonon energies in lanthanum manganites have been determined by dispersing powder in alkali halide matrices and measuring the absorption of far-infrared radiation. The method is illustrated with the classic colossal magneto-resistance material La 0.7Ca 0.3MnO 3. Relative to this, phonon energies associated with the Mn site are found to increase as Li is substituted for Mn. In the absence of Ca substituting for La, a new phonon mode is observed.

CuCl nanocrystals in alkali-halide matrices under hydrostatic pressure

CuCl nanocrystals in crystalline alkali-halide matrices have been investigated under hydrostatic pressures up to 18 GPa. The pressures of structural phase transitions in CuCl have been determined both for different nanocrystal sizes and for different matrices (NaCl, LiCl, KCl). For CuCl nanocrystals in NaCl an increase of the transition pressure with decreasing nanocrystal size is observed, which is explained by the increasing importance of surface pressure for small nanocrystals. We found higher transition pressures for the LiCl matrix than for the NaCl matrix. The reason for this is that the pressure which acts on the nanocrystal differs from the external pressure. A simple elastic model describes the effective pressure transmitted from the matrix to the nanocrystal. With CuCl nanocrystals embedded in KCl we have studied the behavior of nanocrystals during a phase transition of the matrix. Additionally we have determined the pressure coefficients of the exciton energies of the CuCl nanocrystals, which depend on the elastic properties of the matrix.

Thermal studies on the polymorphic modifications of (R,S) propranolol hydrochloride

The polymorphism of (R,S) propranolol hydrochloride was investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray powder diffractometry (XRPD) and thermomicroscopy (HSM) coupled with FT-IR spectroscopy. Propranolol hydrochloride existed in three different crystalline forms, denoted as forms I, II and III, according to their decreasing melting temperatures. Modification II was the commercial product. The forms I and III were obtained by melting form II in different experimental conditions. Form III was obtained only by solidification of the melt in the presence of an alkali halide matrix (as a crystalline film on an alkali halide window or as powder dispersion in a KBr pellet). Forms I and II were also obtained by crystallization from 95% aqueous ethanol and acetone, respectively. The three forms were easily differentiated by their IR spectra in the 3400–2000 cm −1 range. The different crystalline structures of forms I and II were characterized by means of their X-ray powder diffraction patterns.

CuCl Nanocrystals in Alkali Halide Matrices: Determination of Growth Parameters by Exciton Spectroscopy

At low temperatures the absorption spectra of CuCl-doped NaCl single crystals show the Z3 and Z1, 2 excitons of CuCl if CuCl exists in the crystalline state. A procedure is demonstrated for dividing the total oscillator strength observed between 3.0 and 5.5 eV into two parts, one is associated with the crystalline state of CuCl and the other with single copper ions. The excitons show blue shifts as a consequence of confinement effects that permit the determination of the average radius R of the CuCl nanocrystals. The transition from initial growth processes to the regime of Ostwald-ripening is demonstrated for growth temperatures between room temperature and 600 K.

Matrix effects in the infrared examination of methamphetamine salts

The infrared transmission spectra of some hydrogen halide salts of methamphetamine are observed to display significant variations dependent upon the alkali halide matrix in which the salt is dispersed for examination. These effects appear to arise from a chemical exchange of halide ions between the methamphetamine salt and the matrix material, which can complicate the interpretation of the spectra. A strong absorption in the hydrogen-stretching region of the infrared spectrum is found to be particularly sensitive to the anion present in the salt, and changes in the appearance of this absorption band can be revealing of any chemistry between the salt and the alkali halide matrix. The analyst should be aware of this phenomenon in the forensic identification of methamphetamine salts, as well as its possible occurrence with other amine drug substances.

Detection of Organic Substrates in Alkali Halide Matrices Using Room Temperature Phosphorescence

Abstract Room-temperature phosphorescence (RTP) emission was detected from several organic substrates using a solid surface composed solely of alkali salts. This technique yields detection limits comparable to the popular polymer-salt and filter paper methods. More importantly, the alkali halide matrix environment requires no special drying processes, has a simple, reproducible sample preparation procedure, and yields no interfering background RTP.

Quadrupolar interaction in iridium cyanide mixed-ligands complexes in alkali halide matrices by ESR spectroscopy

Quadrupolar interactions in [IR(CN)5]3−, [Ir(CN)5Cl]4− and [Ir(CN)4Cl2]4− paramagnece a complexes in alkali halide host lattices are systematically analysed by ESR spectroscopy. The measured quadrupolar interactions are shown to have no clear correlation to the measured unpaired electron populations.

Quantum size effect on excitons in microcrystals of cuprous halides embedded in alkali halide matrices

Exciton luminescence spectra of CuCl, CuBr and CuI microcrystals embedded in alkali halide matrices are studied experimentally and are explained in terms of the size-quantized excitons with the idea of exciton confinement. From the analysis of the splittings of the exciton states into several components, exciton masses and k-linear terms are derived in these compounds.

Use of 4f7ions to follow strontium precipitation in KCl and KBr

Precipitation of divalent strontium ions in monocrystalline KCl and KBr has been analysed using the Eu2+ ion as an optical and a paramagnetic probe. It has been ascertained that different kinds of Sr second-phase precipitates can be formed in the alkali halide matrix depending on the annealing temperature to which the crystals are subjected. From the optical (emission and excitation) and electron paramagnetic resonance data obtained, some characteristics of these precipitates could be inferred. In particular, the annealing of KCl:Sr:Eu at 473K produces the formation of SrCl2 precipitates, the europium ions being incorporated into these precipitates. The annealing at lower temperatures ( approximately 343K), however, induces the growth of another type of precipitate in which the Sr(Eu) ion occupies a cubic symmetry site with six-fold coordination. The structure of these precipitates could be that of K4SrCl6. A similar situation was found in KBr. The data obtained in this host crystal indicates that the Sr precipitates which are formed by annealing at 343K are different to those which nucleate at 473K. However, it appears that, in both cases, the precipitates have a cubic structure; the cubic site occupied by the Sr2+ ion in the 343K precipitated phase being of a six-fold coordination, while that in the 473K second-phase precipitate being of an eight-fold coordination. Some tentative proposals for the structures of these Sr precipitates are given.

Dimer formation at the earlier stage of dipole clustering in manganese-doped NaCl and KCl.

The aggregation kinetics of nearest-neighbor and next-nearest-neighbor ${\mathrm{Mn}}^{2+}$-cation--vacancy dipoles in manganese-doped NaCl and KCl has been analyzed at 333 and 343 K as a function of impurity concentration. To do this, we measured a large number of dipole- decay data points at short annealing times with use of the electron-paramagnetic-resonance technique. With this technique we achieved a good knowledge of the dipole-decay curve when only a small amount of dipoles had been clustered to form aggregates into the alkali halide matrix. The analyses of the data taken at the earlier stage of aggregation, without our assuming any reaction order a priori, indicates unambiguously that this dependence is the one expected for a pure second-order kinetics equation. From this result and those reported in our previous paper showing conclusively that dimers are the complexes which are formed during the very initial stage of the clustering process, it appears that the long-existing controversy of dimer versus trimer formation may be definitively solved.