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.     

The intensity of triboluminescence

The first values of the absolute triboluminescence intensity, in units of photons/mol, are reported for molecular crystals and salts. The values range from 5 × 10¹⁶ photons/mol for cholesteryl salicylate to 6.2 × 10¹⁰ photons/mol for magnesium sulfate. The mechanical yield of triboluminescence is defined and the lower limit is determined.     

Absorption in zinc sulphide

The absorption coefficient in the absorption edge region of 3400–3200 Å has been measured for orientations of the electric vector of the incident light with respect to the crystalc-axis. The results obtained are compared with measurements on evaporated layers.     

Ion implantation of zinc sulphide

The passivation of argon sputter-etch induced electrically active defects on Ge, Si, and GaAs surfaces by reaction with atomic hydrogen has been observed using deep level transient spectroscopy. A broad band of defect states, giving rise to non-linear Arrhenius plots, appears to be associated with the induced damage centres. For n-type Ge and p-type Si, a 20-min exposure to atomic hydrogen at 180°C is shown to neutralize the damage created by a 5-min, 6 kV (DC), Ar gas sputter-etch. For n-type GaAs a 1-h exposure at 250°C was sufficient, whilst n-type Si required a 1-h exposure to the hydrogen plasma at 300°C to passivate the damage. In each case, to remove the sputter-etch damage by thermal annealing required temperatures approximately 100°C higher, for periods of approximately 2 h.     

On the electroluminescence of powdered zinc sulphide layers

The experimental study of the dependence of the electroluminescence brightness on the voltage confirms the correctness of the mechanism of electroluminescence, based on impact ionization in parts of the crystal where the electric field is concentrated. A study of the photoluminescent and electroluminescent spectra of phosphors containing two activators (copper and an element of rare earth) permits the determination of the magnitude of the volume of the crystal in which electroluminescence occurs. A study of the influence of the stored light sum on the brightness of electroluminescence and a study of the rate of growth of the variable and constant components of electroluminescence point to the fact that the excitation is transferred from the region of field concentration to the whole volume of the crystal.

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The influence of pressure on the luminescence of zinc sulphide single crystals

Experiments were made which show that luminescence originated under the application of pressure on the single crystals of zinc sulphide. The calculated formula gives the same dependence of luminescence on the change of pressure dP/dt as in [1], [2].     

Multiphoton impurity luminescence in zinc sulphide

Impurity luminescence is reported in ZnS(Cu) with two- and three-photon optical pumping. Experimental results are in good agreement with the nonlinear cross-section values obtained from other experiments and from theory.     

Dielectric properties of nano-particles of zinc sulphide

The dielectric properties of nano-particles of ZnS have been studied over a temperature range from 300 to 525 K. The dielectric constant, dielectric loss and ac conductivity of the samples are larger than those of bulk ZnS crystals. Dielectric properties of composites consisting of nano-particles of Ag of different concentrations dispersed in nano-particles of ZnS have also been studied.     

The influence of ball milling on the structure and electroluminescence of zinc sulphide powder

The paper describes the influence of ball milling on the structure and electroluminescent emittance of zinc sulphide powder activated with manganese and copper. It is shown that in the initial stage of ball milling there is a sudden decrease in the EL emittance and later the EL emittance fluctuates. The maximum in fluctuation, however, does not exceed 25% of the initial emittance. The ball milling mechanism of powder and the quenching of its EL emittance was proposed on the basis of measurements obtained by X-ray, spectral and integrated EL emittance as a function of the milling time. From Goldberg's relation for EL emittance a new relation was obtained for the emittance as a function of the structural parameters such as the magnitude of the powder grain, its so-called critical value, and the density of imperfections produced during milling.The author thanks J. Waková from the Research Institute of Inorganic Chemistry in Ústí nad Labem for making it possible to perform the diffractometric measurements in their laboratory, J. Pasterák from the Institute of Physics, Czechoslovak Academy of Sciences, who made it possible to measure the EL spectral emittance, Prof. A. Kochanovská for advice in evaluating the X-ray results, M. Trlifaj, K. Pátek and J. Kubátová for advice in interpreting the EL spectral emittance and A. Kleprlík for help in elaborating the results.     

Four-photon spectroscopy of excitons in hexagonal zinc sulphide

Laser diagnostics of exciton states in ZnS crystal at 80 K, using third-order optical processes, is reported. Expressions of the effective nonlinear susceptibilities for the studied crystal configuration, are obtained. Longitudinal exciton of E = 3.8940 eV energy in hexagonal zinc sulphide is observed for the first time. An assignment to the 1s exciton of B series in ZnS, is made.     

Ion implantation doping of zinc sulphide thin films

This letter reports on the ion implantation doping of zinc sulphide thin films with terbium, erbium and manganese and shows that the resultant cathode-excited emission is characteristic of the implanted ion.     

Formation of hexagonal shaped wurtzite zinc sulphide nano rods

Zinc sulfide nanorods with good photoluminescence have been successfully fabricated using a simple sol-gel process via ultrasonication, with mercaptoethanol as capping agent. The formation of ZnS nucleation, followed by subsequent growth, is significant in obtaining highly oriented ZnS nanorods. Temperature, time, and capping agent also proved to be significant factors in the growth of ZnS nanorods and greatly affect their photo luminescent properties. X-ray diffraction (XRD) analysis, low and high-resolution transmission electron microscopy (TEM & HRTEM), selected-area electron diffraction (SAED) pattern, and scanning electron microscopy (SEM) indicated that the ZnS nanorods were single crystal in nature and that they had grown up preferentially along the [0001] direction. This simple method of nucleation, followed by their successive growth, resulted in the development of an effective and low-cost fabrication process for high-quality ZnS nanorods with good photo luminescent properties that can be applied to luminescent sensors and optoelectronic devices.     

Characterization of luminescence centres in neodymium implanted zinc sulphide

Analysis of the cathodoluminescence emission spectra of neodymium implanted cubic single crystal ZnS as a function of post-implantation annealing temperature has enabled groups of emission lines to be identified as originating from transitions within particular luminescence centres. For each group of lines the wavelength separations yield energy splittings characteristic of the crystal field at the luminescence centre. Comparison of these splittings with values calculated by crystal field theory on the basis of a point charge model, with due regard to possible sites of cubic symmetry in ZnS, has allowed two luminescence centres (A and B) to be identified.Centre A, which exists at low annealing temperatures, consists of a Nd³⁺ ion situated interstitially with 4 tetrahedrally disposed nearest neighbour S^2? ions. At higher annealing temperatures the emissions from centre A were found to decline giving way to those of centre B, which analysis shows to be a Nd³⁺ ion situated on a zinc substitutional site.     

Investigation on self activated and copper activated zinc sulphide

The diamagnetic susceptibility of zinc sulphide decreases on heat treatment and becomes less temperature dependent. The susceptibilities or the differences in susceptibilities of the pure and activated samples do not obey Curie Law. The susceptibility follows a relation of the typeX _T =X ₀ +X ₁ e ^?E/KT in which bothX ₀ andX ₁ have the same sign.X ₀ is interpreted as true diamagnetic susceptibility of the sample and gradually increases in value with activation,X ₁ depends on the particle size and is found to decrease with the increase in particle size. This is interpreted as being due to surface electrons.“E” as measured in this way is found to be of the order of 0·01 ev. in all cases. Thus“E” seems to be the average surface trap depth of zinc sulphide. It has also been found that in zinc sulphide with low copper concentration the luminescent centres are diamagnetic; copper ions are present presumably in substitutional positions. For zinc sulphide containing high concentration of copper, the presence of paramagnetic centres are detected. It is suggested that in this case copper is present not only at the regular lattice positions acting as luminescent centre but also settles at special lattice sites like dislocation jogs.     

Luminescence of isoelectronic traps in laser-annealed,tellurium-coated zinc sulphide

The production of a single-tellurium and paired-tellurium isoelectronic trap luminescence centres in zinc sulphide by the Q-switched ruby laser irradiation of layers of thermally-deposited tellurium on the surface of zinc sulphide is described. Evidence is presented for surface melting of the zinc sulphide caused by the laser radiation. For the production of isoelectronic traps by the above-mentioned process the existence of an optimum energy of the laser radiation has been shown and its approximate value determined.     

Hybrid p-type copper sulphide coated zinc oxide nanowire heterojunction device

A novel heterojunction was formed between zinc oxide nanowires and copper sulphide. The proposed device was fabricated by a fully solution-based process that consists of hydrothermal growth method and chemical bath deposition. The optoelectronic properties of the proposed heterojunction were evaluated by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, UV–vis spectroscopy, photoluminescence measurements and current voltage characteristics.     

Chemisorption of hydrogen sulphide on zinc oxide modified aluminum-substituted SBA-15

Aluminum silicate mesoporous material, ZnO/Al-SBA-15, was synthesized by post-synthesis and immobilization method via microwave-assisted route. Desulphurization tests from a gas mixture with low content H₂S were carried out as the probing reaction on these materials. Chemical effects and the nature of the ZnO additive and textural properties on desulphurization capacity were studied over this material. Material was characterized using N₂ adsorption, XRD, TEM, FTIR, XPS, ICP and other techniques. The analysis suggests that the as-synthesized material had well-ordered hexagonal mesopores and was abundant in micropores. ZnO nanoparticles dispersed well and anchored both in the channel and the wall of mesoporous silica. The material with 2.1 wt.% zinc loading presented the highest H₂S uptake capacity. Both micropores and mesopores are active sites for H₂S capture, especially micropores. The enhancement of H₂S removal capacity was attributed to the integration of the pore structure of mesoporous material and the promising desulphurization properties of ZnO nanoparticles. ZnO/Al-SBA-15 could be an effective alternative to remove H₂S from gaseous streams and it also extends the research of mesoporous material.     

Gudden—Pohl effect and surface states in zinc sulphide phosphors

The classical electrophotoluminescent phenomenon, Gudden—Pohl effect (GPE), is used as a model to demonstrate the influence of surface states on the storage of optical excitation in A²B⁶ semiconductor compounds. Extensive experimental data on the investigation of GPE in ZnSCu phosphors are analysed and two possible approaches to interpretation of this phenomenon are discussed. From experimental data from the papers of Matossi and Riehl, some limitations in applying the model of Curie were determined. According to this model, the light flash of GPE must arise due to the increase of concentration of free electrons, released by the external electric field from electron traps. Also the model of GPE by Gol'dman is considered which relates the flash to recombination of free electrons and holes localized on the luminescence centres when the height of the collective repulsive barrier hindering recombination is decreased by the external field. This barrier is assumed to be created by the surface negative charge. A correlation between the GPE and the state of the persistent internal polarization in luminophors is discussed. This correlation makes it possible to use the light sum of the GPE flash as an optical indicator of the persistent internal polarization. An analogy is made between the GPE and the luminescent field effect for CdS single crystals due to the influence of the surface band bending on the luminescence intensity. The possibility of relating the GPE memory characteristics to the relaxation rate of the surface charge induced by the field is analysed.     

Radiation damage and decay characteristics of zinc selenide emission bands and their equivalence to zinc sulphide emission bands

Irradiation of zinc selenide at ～ 20°K with electrons capable of displacing zinc atoms results in the production of cathodoluminescence emission bands at 610 and 630 nm. Enhancement of the 630 nm emission band by electron damage requires the presence of copper in the samples. These emissions have been shown to give a peak energy shift to lower energies after excitation, as is characteristic of donor-acceptor pair recombination. It is concluded that the 610 and 630 nm emission bands of zinc selenide are equivalent to the self-activated and copper green emission bands of zinc sulphide. The 530 nm emission band of zinc selenide is not sensitive to electron damage, shows no time shift and is thought to be equivalent to the copper blue emission of zinc sulphide.