CuCl Microcrystals Research Articles

Solvothermal synthesis of copper (I) chloride microcrystals with different morphologies as copper-based catalysts for dimethyldichlorosilane synthesis

CuCl microcrystals with different morphologies such as tetrahedra, etched tetrahedra, tripod dendrites, and tetrapods were synthesized using CuCl2⋅2H2O as the copper precursor in the mixed solvent of acetylacetone and ethylene glycol. The samples were characterized with X-ray diffraction, scanning electron microscopy, infrared spectroscopy, and transmission electron microscope. Cu(C5H7O2)2 was identified as the key intermediate, and the morphology and structure of the CuCl microcrystals were highly dependent on the reaction time and temperature, as well as the volume of the solvents. The catalytic properties of these CuCl microcrystals were explored in the dimethyldichlorosilane synthesis via Rochow reaction. Compared to the commercial CuCl microparticles with irregular morphology and dense internal structure, the obtained CuCl microcrystals possessed regular morphology and different exposed crystal planes and showed much higher dimethyldichlorosilane selectivity and Si conversion via the Rochow reaction because of the enhanced formation of active CuxSi phase and gas transportation within the dendritic structure, demonstrating the significance of regular morphology of the copper-based catalysts in catalytic organosilane synthesis.

ChemInform Abstract: Preparation and Nonlinear Optical Properties of Quantum-Sized CuCl- Doped Silica Glass by the Sol-Gel Process.

The sol–gel process has been applied successfully to the preparation of small-sized CuCl-doped silica glass with a significant quantum-sized effect. Gel synthesized by the hydrolysis of a complex solution of Si(OC2H5)4 and CuCl with an HCl catalyst is heated to 900°C to form fine, cubic CuCl crystals. Above 700°C, absorption peaks observed at ∼370 and ∼380 nm are attributed to the excitation of confined Z1,2 and Z3 excitons, respectively, in the CuCl microcrystals. As the size of the CuCl crystals decreases, exciton energy shifts to the higher-energy side. The resonant third-order nonlinear susceptibility at 77 K is 1.1 × 10−8 esu, which originates from the enhancement by the quantum-sized effect of the exciton.

Enhanced luminescence of CuCl microcrystals in a organic-inorganic hybrid matrix

γ-CuCl microcrystals were found to segregate in self-assembled (CnH2n+1NH3)2CuCl4 hybrid organic-inorganic films deposited by single source thermal ablation. The microcrystals dispersed in the hybrid have sizes of 35 nm, as estimated from X-ray diffraction patterns. The UV photoluminescence efficiency of the embedded microcrystals is more than 100 times higher than that of CuCl films having similar crystallite sizes.

Modified copper wire as solid-phase microextraction fiber, selective extraction of some amines

This paper presents results obtained using modified copper wire as a solid-phase microextraction (SPME) fiber. Modified copper fibers were prepared by dipping cleaned copper wires (350 μm o.d.) in a solution of CuCl2. Scanning electron microscopy experiments suggested the formation of a thin layer of CuCl microcrystals (d.p.<1 μm) on the metal surface. These fibers were used for the extraction of some volatile amines from gaseous samples. Extracted analytes were transferred to a GC injector using a homemade SPME device. Results obtained show that the proposed fiber has high selectivity and good recovery for extraction of amines. More than 83% of primary amines were extracted in 5 min from 50 mL gas sample with a relative standard deviation (RSD) <0.5% (n=5). Calibration graphs were linear in the range 0.3–15 ng mL−1 for primary amines. The detection limit was 0.1–0.3 ng mL−1 (S/N=3) using a flame ionization detector.

The Nature of Thermochromic Effect in Glasses with AgCl and CuCl Microcrystals

The nature of the thermochromic effect is investigated in glasses containing AgCl microcrystals (MC). At temperatures above the melting point of microcrystals, the absorption spectrum consisting of two bands transforms into a single, very narrow, and intense band. This band is similar to absorption bands that appear in the spectra of silver-containing systems under the conditions ensuring metal coagulation. A model of the thermochromic process is proposed. According to this model, the narrow band is attributed to the spherical metal layer adsorbed on the wall of the cavity containing the AgCl melt. After the crystallization of AgCl, metallic islands in the form of oblate ellipsoids remain instead of the spherical layer. The role of secondary glass-formers is analyzed, and the evidence for the existence of a similar effect in glasses with CuCl is obtained.

An Alternative Model for Photochromism of Glasses: Reversible Injection of Carriers from a Microcrystal and Its Surface States into Point Defects of Glass

The radiation-induced absorption spectra of photochromic homogeneous silicate glasses and heterogeneous borosilicate glasses containing AgCl, AgBr, or CuCl microcrystals are analyzed. The inference is made that these spectra contain the bands of traditional radiation-induced color centers (RICCs) in glasses and the bands of halide defects in microcrystals. The band model of the photochromic process in the “microcrystal–surface states–glass” system is proposed on the basis of the performed analysis with due regard for burning of the exciton hole in the induced spectrum of CuCl-containing glass. This model makes it possible to explain a large number of experimental data.

Exciton and biexciton properties of CuCl microcrystals in an SiO 2 matrix prepared by sputtering method

We investigated the optical properties of the exciton and the biexciton in CuCl microcrystals embedded in an SiO 2 matrix which is prepared by a novel RF-magnetron sputtering combined with an inductively coupled plasma. The exciton absorption bands of Z 3 and Z 1,2 in CuCl microcrystals shift to energies higher than those for the bulk excitons. In the luminescence spectra intensities of the free exciton and the biexciton luminescence bands under wide excitation density range have linear and superlinear dependencies, respectively: the value of power dependence of the biexciton luminescence bands is about 1.4.

Quantum Size Effect of CuCl Microcrystals-Doped SiO&lt;sub&gt;2&lt;/sub&gt; Glass Thin Films

CuCl microcrystals-doped SiO2 glass thin films were successfully prepared by rf (radio frequency)-sputtering method. The formation of CuCl microcrystals in the glass thin films has been explored by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The quantum size effect in CuCl was found from the blue shift of exciton absortion peaks. Although some influence of the matrix on the temperature dependent linewidth of the exciton peaks was observed, the relationship between the amount of blue shift of the absorption edge and the diameter of the CuCl microcrystals satisfied the theory for the quantum-size confinement of the exciton.

High-Temperature UV-Vis Spectroscopic Investigations on the Second Annealing Process of Photochromic Glasses

A second annealing process of silver- or cuprous halide microcrystals containing glass changes their photochromic behaviour. The second annealing is carried out both below Tg of the glass and below the melting point of the crystals. In situ UV-VIS spectroscopic measurements in this temperature range indicate changes in excitonic peaks of CuBr or CuCl microcrystals as function of temperature, annealing time and cooling rate. Room temperature spectra of irradiated samples show a direct dependence on the conditions of the second annealing process. The decrease in the transition temperature of these small crystals below the bulk value causes partiy transitions of the low temperature modification of the crystals into the high temperature modification, that does not contribute to excitonic absorptions and darkening ability.

Excitonic optical nonlinearity of CuCl microcrystals in a NaCl matrix

Absorption and luminescence saturation of confined excitons are measured using a single-beam method for CuCl microcrystals with various radii embedded in NaCl single-crystalline matrices. From the excitation-intensity and microcrystal-size dependencies of their saturation, the effective saturation density of excitons, which is inversely proportional to the magnitude of optical nonlinearity, proves to be inversely proportional to the volume of microcrystals with effective radii of less than 5 nm at 77 K. Therefore, the optical nonlinearity of these microcrystals is not a function of microcrystal radii, but of the number of excitons created in a microcrystal, indicating the characteristic nature of coherent exciton confinement.

Interface effects on the properties of confined excitons in CuCl microcrystals

Optical properties of confined excitons were studied in nanometer-size CuCl microcrystals prepared by three different methods; by annealing in crystalline NaCl and in glass matrices, and by gas evaporation. Interface effects concerning the shape of microcrystals, the effect of finite barrier height and the photo-generated exciton trapping centers were discussed.

Optical spectra of free and supported CuCl microcrystals produced by thermal evaporation in a helium gas stream

Time-resolved measurements of the extinction spectra of free CuCl microcrystals and of CuCl microcrystals collected on a glass substrate have been performed at various growth stages after the beginning of evaporation in a low-pressure helium gas. Absorption bands due to Z1,2 and Z3 excitons were observed, which were shifted in energy from their bulk positions owing to exciton confinement effects. Initially the energy difference between the Z1,2 and the Z3 bands is considerably larger than its bulk value, and with increasing time it decreases and approaches the bulk value. The observed Z3 exciton absorption bands are compared with those calculated using an extended Mie theory, in which non-local effects as well as the size quantization of the excitonic states are included.

Biexciton lasing in CuCl quantum dots

Lasing of CuCl microcrystals embedded in a NaCl single crystal was observed for the first time. The lasing takes place at 77 K in a sample sandwiched between dielectric mirrors under pulsed ultraviolet laser excitation. The lasing transition is that from biexciton to exciton. The lasing is observed up to 108 K. The optical gain of the sample is almost the same as that of a CuCl bulk crystal in spite of the low concentration of CuCl in the NaCl matrix.

Size selective nonlinear optical spectroscopy of excitons in CuCl quantum dots

A size selective pump-and-probe method was applied to the Z 3 exciton absorption spectra of CuCl microcrystals. Observation of the spectral hole-burning gave us the size-dependent homogeneous linewidth at 2 K. The size-dependent part of the homogeneous linewidth is inversely proportional to the square of the radius of microcrystals. This dependence is explained by the scattering of excitons at the irregular surface of microcrystals. With the increase in the excitation density, the lower energy absorption is bleached and the higher energy absorption is enhanced. The high density excitation effect is explained by both the radiative energy transfer between microcrystals and the exchange interaction of excitons in microcrystals.

Quantum size effect of excitonic molecules in CuCl microcrystals

The quantum size effect of excitonic molecules confined in microcrystals of CuCl is studied theoretically by a variational calculation for a simplified model. The excitons are approximated as quasiparticles confined in a microsphere with the effective radius R* and interacting with each other through the Morse potential. It is shown that the peak energy of the excitonic molecule luminescence shifts to the lower energy side from the bulk value for relatively large values of R* but shifts to the higher energy side as R* is decreased further, in agreement with the experimental observation. By fitting the theoretical value of the peak energy shift with the experimental values, it is shown that the minimum point of the Morse potential is at about 1 nm and the separation between the center of mass of the two excitons is about 1.5 nm in the bulk crystal.

Size-dependent homogeneous linewidth of Z3 exciton absorption spectra in CuCl microcrystals

Size-dependent homogeneous linewidth of Z3 exciton absorption spectra in CuCl microcrystals was measured at 2 K by the pump-and-probe spectroscopy. Observation of the hole burning gave us the homogeneous linewidth. The size-dependent part of the homogeneous linewidth is inversely proportional to the square of the radius of microcrystals. This dependence is explained by a simple model that a generated exciton dephases through the scattering at the irregular surface of microcrystals.

Anomalous change of extinction spectra of CuCl microcrystals

Optical transmission spectra of CuCl microcrystals embedded in NaCl crystals were studied around the Z3 exciton resonance by varying the annealing time. With the increase in the annealing time, extinction spectra of the Z3 exciton change anomalously from the absorption-type spectrum to the emission-type spectrum via the dispersion-type spectrum. The Mie theory [Ann. Phys. 25, 377 (1908)] successfully explains the spectral change due to the growth of microcrystals. We report here for the first time an anomalous change of the exciton spectra due to the growth of semiconductor microcrystals.

Size-dependent homogeneous broadening of confined excitons in CuCl microcrystals

In nm-size CuCl microcrystals embedded in NaCl matrices, resonant luminescence spectra of the Z 3 confined excitons were measured under size-selective excitation among the exciton absorption band, inhomogeneously broadened due to the size-distribution of the microcrystals. The temperature- and size-dependences of the homogeneous line width of the confined exciton absorption with the lowest energy could be derived from the bandwidth of the exciton resonant luminescence. Based on the analysis similar to that for the line width of the free excitons in a bulk crystal, it is found that with decreasing microcrystal size the short-range deformation-type interaction of confined excitons with LA phonon becomes more and more important for the broadening, mainly because of the localization of the vibrational motion, while the Fröhlich-type interaction with LO phonons does not change much on account of its long-range interaction.

Preparation and Nonlinear Optical Properties of Quantum‐Sized CuCl‐Doped Silica Glass by the Sol–Gel Process

The sol–gel process has been applied successfully to the preparation of small‐sized CuCl‐doped silica glass with a significant quantum‐sized effect. Gel synthesized by the hydrolysis of a complex solution of Si(OC2H5)4 and CuCl with an HCl catalyst is heated to 900°C to form fine, cubic CuCl crystals. Above 700°C, absorption peaks observed at ∼370 and ∼380 nm are attributed to the excitation of confined Z1,2 and Z3 excitons, respectively, in the CuCl microcrystals. As the size of the CuCl crystals decreases, exciton energy shifts to the higher‐energy side. The resonant third‐order nonlinear susceptibility at 77 K is 1.1 × 10−8 esu, which originates from the enhancement by the quantum‐sized effect of the exciton.

Nonlinearities of CuCl Microcrystals

AbstractUsing a “pump and probe” technique, a strong blue shift and a bleaching is measured of the Z3 excitonic absorption line of CuCl microcrystallites embedded in glass. These effects are attributed to exciton exciton‐interactions. They show a response time shorter than the nanosecond. This seems to be mainly due to a fast non‐radiative decay of the excitonic population, leading to a heating‐up of the microcrystals.