Growth and luminescent properties of the Ce,Pr doped NaCl single crystals grown by the modified micro-pulling-down method

We have investigated luminescent properties of nondope, Ce and Pr doped NaCl [nondope NaCl, Ce:NaCl, Pr:NaCl] single crystals grown by a modified micro-pulling-down method with a removable chamber system. Nondope, Ce 1% and Pr 1% doped NaCl crystals with a single phase of NaCl structure were obtained and the crystals indicated general crystal quality by the X-ray rocking curve measurement. For the nondope NaCl and Pr:NaCl crystals, the transmittance spectra indicated almost more than 60% in the wavelength from 200 to 800 nm and an absorption of Ce³⁺ ion was observed in the transmittance spectrum of Ce:NaCl crystal. The emission spectrum originated from Ce³⁺ 5d–4f transition appeared around 300 nm in the photoluminescence spectrum and the decay time was 19.7 ns.     

Magnetosensitive intermediate states of point-defect complexes formed as a result of quenching of NaCl: Eu single crystals

A correlation between temporal variation in the optical and mechanical properties of quenched NaCl: Eu single crystals and the sensitivity of these crystals to a constant magnetic field was found. The results obtained make it possible to assess the atomic structure of magnetosensitive point-defect complexes.     

Struktur- und Absorptionspotentiale von KCl und NaCl aus Beugungsaufnahmen im konvergenten Elektronenbündel

By improvement of an earlier published preparation method for producing thin single crystals soluble in water, it is possible to determine structure and absorption potentials of some reflections of KCl and NaCl crystals by a convergent beam diffraction technique. The structure potentials evaluated on the basis of the two-beam dynamical theory are found to depend on the thickness of the crystals used. The structure potentials corrected for relativistic, thermal and many-beam effects are compared with theoretical values. The measured (220)- and (420)-absorption potentials of NaCl are in good agreement with theoretical values. Radiation damage in KCl and NaCl crystals by electron beams is observed.     

从昇华的NaCl蒸汽生长单晶体

半个世纪以来,从NaCl的蒸汽生长其单晶体的企图并没有得到正面的结果,解理面上的取向性结晶也尚未有超过数个分子层者。对于从溶液结晶出来时NaCl晶面发展的顺序,或者相对的重要性的研究已有肯定的结果。关于晶核或生长驼峰发端的位置从几率上看应在晶面何处的时尚理论未能从NaCl自溶液中结晶出来的实验加以证实或否定。为探索从蒸汽相生长NaCl单晶体的规律,本实验初步获得较大尺度的单晶体,并同时使取向性晶面上结晶达到1毫米以上的厚度。升华蒸汽来源于高纯度的从熔融体结晶出来的单晶体,并使母晶和结晶基面保持在近于NaC     

Size-Frustrated Thickening Growth of Extended-Chain Crystals in a Poly (Ethylene Terephthalate)/Bisphenol A Polycarbonate Blend Under High Pressure

High-pressure crystallized blend samples of poly (ethylene terephthalate)/bisphenol A polycarbonate (PET/BAPC) were investigated with scanning electron microscopy (SEM), confocal laser micro-Raman spectroscopy, and a standard general area detector diffraction system (GADDS) X-ray micro-diffraction system. The results showed that long time annealing at high pressure could result in extended-chain polymer single crystals with thicker lamellae. However, the large size of such crystals was also found to frustrate their thickening growth along the c-axis thickness, as demonstrated by the observation of a novel wrinkled crystal. The winkled crystals with different morphologies were thought to be formed as the compromise between the kinetic pathway and the thermodynamic driving force during the size-frustrated thickening growth of the large polymer crystals. Further observations revealed that environmental confinement was the main factor responsible for the creation of the wrinkled structures in polymer extended-chain crystals. The present study may promote understanding of the fundamental nature of the crystal thickening in these binary polyester blends.     

Synthesis,growth and studies of undoped and sodium chloride-doped Zinc Tris-thiourea Sulphate (ZTS) single crystals

Single crystals of undoped (pure) and sodium chloride (NaCl)-doped Zinc Tris-thiourea Sulphate (ZTS) were grown from aqueous solutions by slow evaporation technique. Morphological alterations have been observed when NaCl is doped into ZTS crystals. Density of the grown crystals was measured by floatation method. The values of unit cell parameters from single crystal X-ray diffraction (XRD) studies show that pure and sodium chloride-doped ZTS crystals are in orthorhombic structure. Impurity concentration in the doped crystals was estimated by using an atomic absorption spectrometer. Second Harmonic Generation (SHG) test for the undoped and NaCl-doped ZTS crystals was performed by the powder technique of Kurtz and Perry using a pulsed Nd:YAG laser. Microhardness studies show that hardness number (H_v) increases with load for all the grown crystals of this work. From the values of work hardening coefficients, it is concluded that pure and sodium chloride-doped ZTS crystals belong to the category of soft materials. UV–vis–NIR spectra show that the grown crystals have wide optical transparency in the entire visible region. Birefringence studies of the grown samples have been performed by channelled spectrum method. The thermal stability of the materials is found to be increasing with the doping concentration of sodium chloride (NaCl) in the lattice of ZTS crystals.     

Softening of ionic crystals as a result of a change in the spin states of structural defects under paramagnetic resonance conditions

The purpose of this work was to investigate the plastic properties of Ca-or Eu-doped NaCl and KCl single crystals in crossed constant and microwave magnetic waves under paramagnetic resonance conditions. It was found that when the photon energy of the microwave field equals the Zeeman splitting of the electronic spin sublevels, resonance softening of the crystals, manifested as an increase in the free path of individual dislocations and the macroplastic flow velocity as well as a decrease of the microhardness of the crystals, is observed. It was established that metastable Ca-and Eu-impurity complexes, which are also sensitive to the constant magnetic field in the absence of the microwave field, as well as complexes formed by dislocations and point defects are responsible for resonance softening.     

A new colour centre in NaCl

A new absorption band at 640 nm is reported in NaCl powder coloured by γ-rays under F-light. The band was not observed in single crystals and the powders coloured in dark. It is tentatively attributed to electrons trapped in dislocation debris — the so-called E centre.     

A sectioning technique for sodium chloride single crystals and its application for ion implantation studies

A sectioning technique for sodium chloride single crystals has been developed. This technique, which is based on the formation of a silver chloride film, is capable of removing layers of constant thickness up to 2μg/cm². Being insensitive to radiation damage of the. NaCl-surface this film technique can be applied in studies of penetration and diffusion in NaCl. An electro-magnetic isotope separator has been used to implant radioactive phosphorous, krypton and xenon atoms in single crystals of sodium chloride, and examples are shown where the film technique has been applied for the study of range distributions and diffusion processes.     

A correlation between manifestations of the magnetoplastic effect and changes in the electron paramagnetic resonance spectra after quenching of NaCl: Eu single crystals

The electron paramagnetic resonance (EPR) spectra of Eu²⁺ impurity ions in NaCl: Eu single crystals are investigated. It is found that the intensity of the EPR spectra undergoes prolonged (～200 h) multistage variations after quenching of NaCl: Eu single crystals. The variations observed in the EPR signal intensity are explained by the aggregation of impurity-vacancy dipoles into complexes. It is revealed that the magnetoplastic effect (a change in the microhardness in a magnetic field with an induction of 6 T) in these crystals manifests itself at an intermediate stage of impurity aggregation when all individual impurity-vacancy dipoles are temporarily stabilized in the sample. This can be associated with the thermally activated transformation of the internal atomic structure in the majority of already existing complexes.     

Formation of radiation defects in single crystals of NaCl and kcl irradiated with channeled electrons with energies 10‐50 keV

We present the results of investigations of the process of formation of F-centers in single crystals of NaCl and kCl upon exposure to 10–50 keV electrons with the incident electron beam directed at various angles to the crystallographic axes < 100> of single crystals. We showed that when the electrons are channeled, the rate of formation of F-centers increases, and the concentration of F-centers near the surface of the single crystals increases. We established a connection between the observed orientation phenomena in the formation of F-centers and the radiation dose and initial energy of the electrons. We determined characteristic angles for channeling the electrons.     

Diffusion and solubility of SO2-4 in NaCl and KCl single crystals

We describe a new and very accurate method for measuring as a function of temperature the solubility of very slightly soluble salts (≈ 10^-5) in single crystals. The method is applied to the systems NaCl, Na₂SO₄ and KCl, K₂SO₄ and to the preparation of SO^2-₄ doped KCl single crystals. The parameters for diffusion of SO^2-₄ at infinite dilution into NaCl and KCl have been measured in the intrinsic range.     

EPR of Mn2+ and Eu2+ ions in the bulk and on the surface of AIBVII type single- and microcrystals

A new dimensional effect is investigated. It consists in a change of the microstructure of bulk impurity defects after a decrease in the crystal size. The results of studying the changes in the defect structure in (NaCl, KCl, LiF):Mn²⁺ and (NaCl, KCl, KBr):Eu²⁺ by electronic paramagnetic resonance (EPR) are presented. Samples of different sizes and nature are investigated: bulk-doped single crystals of large sizes; bulk-doped crystals of small sizes; powder samples of various degree of dispersity, which are obtained by crushing the samples of large sizes; and samples with direct doping of the surface. The spectra of three types are measured: the spectra of single crystals; the spectra of the powders with the sizes of the particlesd ≥ 1 mm; the spectra of the powders withd ≤ 3 μn (analogous spectra have the surface-doped samples). Considerable change in the EPR spectra as the samples are continuously crushed is due to the change of the paramagnetic center (PC) structure. In the case of bulk-doped single crystals the paramagnetic ion compensator is in the nearest cation coordination sphere. When the deformation caused by the surface region becomes large enough in the vicinity of PC, detachment and removal of the compensator from the impurity ion take place. As a result, the local symmetry of the PC is changed and is revealed in the EPR spectra.     

The mechanism of the appearance of an electromotive force on heating of SmS single crystals

We analyze the experimental variation of the concentration of conduction electrons in semiconducting SmS single crystals with increasing temperature within a shallow-impurity model. It is shown that the appearance of an electromotive force is due to accumulation of the critical concentration of free electrons, which results in screening of the Coulomb potential of Sm²⁺ impurity ions that are responsible for the creation of donor levels with an activation energy of 0.045 eV in the band gap of SmS single crystals.     

Growth,structural, mechanical,spectral and dielectric characterization of NaCl-added Triglycine sulfate single crystals

Pure and sodium chloride (NaCl)-added Triglycine sulfate (TGS) crystals were grown from aqueous solutions by slow evaporation technique. The values of concentration of dopants in the mother solution were 0.2, 0.6 and 1 mol%. The solubility of the grown samples have been found out at various temperatures. The determination of unit cell parameters was carried out by single crystal XRD method and found that the grown crystals crystallize in monoclinic structure. The dielectric characterization for the pure and NaCl-doped TGS crystals was performed by measuring the dielectric parameters like dielectric constant and dielectric loss with various frequencies in the range 10²–10⁶ Hz and with the temperatures ranging from 30 to 70 °C and this study reveals an increase of dielectric constant and loss with the increase of NaCl concentration. Studies on mechanical properties like microhardness and density of the grown pure and NaCl-doped TGS crystals were carried out. UV–Visible transmittance studies were carried out for the grown samples. A sharp fall in the transmittance is observed at 228 nm for pure and NaCl-doped TGS crystals. Atomic absorption spectroscopic (AAS) study was done on the NaCl-doped TGS crystals to ascertain the presence of Na⁺ ions in the lattice.     

Study of the IR photoionization spectrum of electronic states generated under plastic deformation of colored NaCl crystals

Physics of the Solid State - This paper reports on the results of an experimental study of IR photoconductivity induced in NaCl single crystals colored under gamma irradiation and subjected to...     

The stress of plastic flow and the dislocation density in sodium and potassium chlorides

The dependence of the dislocation densities inside and on the surface of NaCl and KCl crystals on the applied compression stress is investigated by means of the hole-etching method. It is found that this relationship varies not only with the temperature but also when the crystals are illuminated by the light from an incandescent lamp. A possible explanation of the effect is given.In conclusion the author would like to thank N. G. Shakman and V. A. Makara, students of the physics faculty of Kiev State University for their help with the measurements.     

On the Transparency of Alkali-Halide Crystal in the Terahertz Spectral Range

Optics and Spectroscopy - The transmission of THz (to 3000 μm) radiation by alkali halide single crystals of sodium chloride (NaCl), potassium chloride (KCl), potassium bromide (KBr), and...     

Effect of temperature and ionizing radiation on the Eu-Mn pair in NaCl

In the present paper photoluminescence measurements have been carried out in single crystals of NaCl doubly doped with Eu²⁺ and Mn²⁺ ions in order to determine the influence of annealing temperature and ionizing radiation on the Eu-Mn pairs which are formed preferentially in this material. From the results obtained it appears that the NaCl:Eu:Mn system may be employed not only as a good device for optical convertion of U.V. light into visible, being sure that its efficiency is not affected by the aggregation-precipitation processes of the manganese ions occurring in the matrix, but also as an efficient photo-luminescence dosimeter.     

Kinetics of transformation of Eu<Superscript>2+</Superscript> dimers in NaCl crystals in a static magnetic field of 15 T

A static magnetic field of up to 15 T is found to affect the photoluminescence excitation spectra of NaCl: Eu crystals. The magnetic field has an effect on the excitation spectra starting at the stage at which dimers are formed through diffusion in the crystals. At earlier stages of impurity aggregation, the magnetic field affects the kinetics of dimer accumulation. It is revealed that the dimer transformation stimulated by the magnetic field involves stages that last for 10–15 min at room temperature in a static magnetic field of 15 T and, hence, are shorter than the aggregation time. Luminescence studies of dimers, which are the main dislocation stoppers in NaCl: Eu crystals, make it possible to explain the specific features of the magnetoplastic effect observed previously in these crystals.