Frequency dependence of electroluminescence processes in ZnS crystals

The frequency dependence of the integral electroluminescence brightness and the electrical conductivity of ZnS-Cu, Cl and ZnS-Mn single crystals was examined. It was established that the correlation between the integral electroluminescence brightness and the electrical conductivity in ZuS-Cu, Cl crystals improves slightly at high frequencies of the exciting field, whereas no such correlation exists for the frequency range 30 Hz-18 Hz in ZnS-Mn crystals. Conclusions regarding the various excitation mechanisms of the electroluminescence in ZnS-Cu, Cl and ZnS-Mn crystals are drawn.In conclusion, the authors express their sincere gratitude to P. E. Ramazanov for his valuable advice.     

Electroluminescence of ZnS-Mn Single Crystals

The electroluminescence (EL) spectra of ZnS-Mn single crystals on excitation by constant and alternating electric fields E 10³–10⁴ V/cm were investigated. It is shown that the electroluminescence of the ZnS-Mn single crystals is related to a pre-breakdown one, during which the electric field is concentrated in the barriers formed by partial dislocations in the places where they break packing defects.     

On avalanche processes in electroluminescence of single ZnS-Cu crystals

The electrical, photoelectrical and luminescent properties of single crystals (30 to 50 microns in size) of commercial ZnS-Cu electroluminophore with green emission have been investigated. The dependencies of dark current, photocurrent and luminescence brightness on the applied voltage have been found to reveal a greater complexity than those obtained for polycrystal samples.When the d.c. voltage applied to the crystal rose above 4 volts the dark and photo electrons were observed to multiply, this being accompanied by emission. The observed dependence of the multiplication coefficient on the applied voltage resembles in shape the curves obtained for other substances (Ge, Si, ZnO).     

Influence of milling of electroluminescent powders ZnS-Cu on their integral and spectral intensity of radiation

Milling of electroluminescent ZnS-Cu powders causes changes in their structure. In its consequence centers of lumincescence are destroyed, the integral intensity of electroluminescent, photoluminescent and roentgenoluminescent radiation decreases and the spectral intensity of luminescent radiation changes, too. On this basis the location of centres of luminescence and forming of glow-complexes in ZnS-Cu crystallites are discussed. The results show that the emission of ZnS-Cu powders is probably due to two glow-complexes. The centers of luminescence of one of them are located near the borders of coherent domains while the centers of the other glow-complex are inside coherent domains of the luminescent powder.     

The photodielectric effect in ZnS-Cu monocrystals

The frequency dependence of the photodielectric effect, transition-process kinetics, and peculiarities of IR light action on tan are studied. It is shown that a photodielectric effect of the first type occurs not only in ZnS-Ag crystals but also in ZnS-Cu crystals.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 40–43, January, 1976.     

Dependence of the intensity of Gaussian components of electroluminescence spectra on the alternating-voltage frequency

The spectra and quantum intensities of ZnS-Cu and ZnS-Cu, Al luminescence are studied as functions of alternating-voltage frequency. An analysis of these two functions indicates that the total emission is basically due to the emission of six Gaussian components whose amplitudes are frequency dependent. A comparison of electroluminescence and photoluminescence brightness for an identical spectral composition leads to the conclusion that the volume in which electroluminescence takes place is much smaller than the volume of photoluminescence emission.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 99–103, December, 1972.     

Relation between crystal structure and electroluminescence in ZnS-Mn crystals

The electroluminescence of ZnS-Mn crystals annealed in zinc melt is investigated. When an external field of 10³-10⁴ V/cm is applied, continuous radiation is emitted over the whole volume of the spcimen. The volt-brightness characteristics are approximated by various functions and depend on the conditions of excitation. The results obtained are explained by the concentration of the electric field at barrier formed by partial dislocations at the place where they cut the hexagonal layers.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 33–37, September. 1985.     

ЭЛЕКТРОЛЮМИНЕСЦЕНЦ ИЯ СУЛЬФИДА ЦИНКА

The processes determining the mean electroluminescent brightness and the time distribution of the brightness in powder ZnS-Cu luminophore are studied. The efficiency of electroluminescence was measured for this luminophore as a function of the voltage.     

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.     

Afterglow of manganese centres in pulse-excited ZnS:Mn

The afterglow of self-activated and manganese centres in ZnS-Mn by excitation with a pulsed nitrogen laser is investigated. Assuming that a time-independent part of the excited “blue” centres returns to the ground state under energy transfer to the “yellow” centres, an equation describing the decay kinetics is derived. The comparison with the experimental data shows satisfactory agreement in the time interval up to 120 μs. A maximum in the afterglow curve arises within this limit.     

Periodic triboluminescence of zinc sulphide

Powdered ZnS-Mn (Cu, Ag) was scattered in the form of a suspension in different solids. The mechanical excitation of triboluminescence was periodic with a frequency of 50 Hz. The resultant triboluminescence is also periodic if the exciting pressure does not exceed 700 kg/cm². The creation of triboluminescence does not depend on the kind of surrounding medium.     

Growth and high pressure studies of zirconium sulphoselenide single crystals

Transition metal trichalcogenides are well suited for extreme pressure lubrication. These materials being semiconducting and of layered structure may undergo structural and electronic transition under pressure. In this paper authors reported the details about synthesis and characterization of zirconium sulphoselenide single crystals. The chemical vapour transport technique was used for the growth of zirconium sulphoselenide single crystals. The energy dispersive analysis by X-ray (EDAX) gave the confirmation about the stoichiometry of the as-grown crystals and other structural characterizations were accomplished by X-ray diffraction (XRD) study. The variation of electrical resistance was monitored in a Bridgman opposed anvil set-up up to 8 GPa pressure to identify the occurrence of any structural transition. These crystals do not possess any structural transitions upto the pressure limit examined.     

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.     

Dynamics of the luminescence spectra of ZnS-Cu and ZnS-Ag crystalline phosphors in atomic hydrogen

It is shown that the luminescence spectra of the ZnS-Cu and ZnS-Ag crystalline phosphors excited by hydrogen atoms depend on the time of exposure of a sample to hydrogen atoms. The changes in the spectra manifest themselves in the redistribution of the luminescence energy. The nature of these changes and the mechanisms of luminescence excitation by hydrogen atoms are discussed.     

The kinetics of the triboluminescence of zinc sulphide I

The paper proposes a two-stage model of the time dependence of triboluminescence as a function of the magnitude of the applied exciting pressure; it is confirmed by the results of measuring the time dependence of triboluminescence. The decay of triboluminescence excited by a blow and by friction is measured. The spectral dependence of triboluminescence in ZnS-Mn was found. It has the same form as in photoluminescence and in addition contains maxima corresponding to the electric discharge in air.     

Crystal growth and luminescence properties of CuI single crystals

Recently, much attention has been attached to the material of cuprous iodide (CuI) single crystals. In this paper, a detailed study of the variation in the nucleation density and the growth of CuI crystals in silica gel as a function of the concentration of feed solution, pH of gel, gel aging time, growth temperature and volume of the feed solution is presented. The optimum conditions for growth of large size CuI single crystals in gel are: pH 5, concentration of complex 0.244 M, gel aging 72 h, temperature 45 °C. A simple procedure for increasing the size of the crystals is adopted and the CuI single crystal with the size of 4 mm³ is obtained. Also, the photoluminescence (PL) spectrum of as-grown CuI crystals in silica gel is evaluated by comparing its PL spectra with that of CuI crystals grown by solvent evaporation method. The results could provide a useful clue to further improve the properties of CuI single crystals.     

The dependence of EPR linewidth on concentration in Mn/MgO single crystals

The EPR spectra of Mn/MgO single crystals grown by electrofusion have been examined at 9 GHz for manganese concentration of between 840 and 2900 ppm. The values of the spin Hamiltonian parameters deduced agreed well with those previously reported by Low (1957, 1958) and by Matarrese and Kikuchi (1956). The variation of linewidth with manganese concentration was also examined and compared with the predictions of the de Biasi and Fernandes theory of dipolar broadening in magnetically dilute systems; the peak-to-peak linewidth is concentration dependent and is of the right order of magnitude to be explained adequately in terms of this model. The results indicate that clustering, effects are absent in these Mn/MgO single crystals.     

Synthesis,crystal growth and characterization of novel semiorganic nonlinear optical crystal: Dichloro(beta-alanine)cadmium(II)

Semiorganic nonlinear optical material of dichloro(beta-alanine)cadmium(II) (DCBAC) have been synthesized and single crystals were grown by solvent evaporation method at room temperature. The lattice parameters of the grown crystals are determined by single crystal XRD. The modes of vibration of different molecular groups present in the sample were identified by the FTIR spectral analysis. Thermal stability of the crystal was investigated using thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). The dielectric constants of the crystal were studied as a function of frequency and the results are discussed. The grown crystals are subjected to microhardness studies and the variation of the microhardness with the applied load is studied. The optical transmission spectra and second harmonic generation (SHG) were investigated to study its linear and nonlinear optical properties. The nonlinear optical (NLO) property of the crystal was confirmed by powder second harmonic generation (SHG) test. SHG efficiency is comparable to that of KDP.     

Some optical properties of (ZnS)−(GaP) alloys and their interpretation

Optical measurements on the single crystals of the pseudobinary (ZnS)?(GaP) alloy were carried out. The band gap energy decreased more rapidly with increase in GaP concentration than that reported previously. The analysis of the absorption spectra for the crystals of up to 70 mole % GaP indicated a direct transition characteristic, and that the band gap becomes nearly equal to that of pure GaP at about 30 mole % GaP. The photoluminescence spectra observed at liquid nitrogen temperature could first be resolved into three kinds of emission band with Gaussian distribution. The peak energy of these bands were found to be independent of the band gap variation. Thus the observed peak energy shift with alloy composition was attributed to the variation of the emission intensity of each band. The band gap shrinkage and the origin of the photoluminescence spectra on the basis of a molecular orbital method were discussed.