INFLUENCE OF LEAD IONS ON PHOTOLUMINESCENT PROPERTIES OF POLYMETHYL METACRYLATE /(Zn,Pb)S/CdS/(Zn,Pb)S COMPOSITIONS

The paper presents the results of a study of the effect of lead ions on the photoluminescent properties of core / shell / shell nanostructures based on zinc and cadmium sulfides synthesized in situ during the formation of polyacrylate composition. ZnS/CdS/ZnS and (Zn,Pb)S/CdS/(Zn,Pb)S nanoparticles were obtained by colloidal synthesis in a medium of (poly) methyl methacrylate. Colloidal solutions are solidified to a glassy state by radical thermal polymerization of methyl methacrylate in a block. To initiate the polymerization, benzoyl peroxide was introduced into the solutions in an amount of 0.1% by weight of methyl methacrylate. The conclusion on the formation of nanosized particles of complex composition in the polymer matrix is made by comparing the luminescence and luminescence spectra of the compositions containing ZnS and CdS particles and their structure. In the photoluminescence spectra of the (poly) methyl methacrylate/(ZnS/CdS/ZnS) composition, two complex bands associated with crystal lattice defects of ZnS particles (380 - 530 nm) and CdS (530 - 840 nm) were detected. The excitation of photoluminescence occurs as a result of interband transitions of electrons in each of the semiconductor layers, as well as during transitions of electrons from the conduction band to defect levels located in the forbidden band of the semiconductor structure. In the luminescence excitation spectrum, they correspond to bands of various intensities in the range of 300–420 nm and 300–480 nm. From the overlap of the ZnS luminescence bands and the excitation of CdS luminescence, it was concluded that the radiation of the core is absorbed by the CdS coating layer and that energy is transferred from the levels of structural defects of ZnS to the levels of structural defects of CdS at the layer boundary. Doping of zinc sulfide layers with lead ions leads to a change in the luminescence spectrum in the region of 380 - 530 nm and the disappearance of the CdS luminescence band in the range of 530 - 840 nm. The observed changes are associated with defects that create Pb2+ ions in the crystal lattice of the ZnS outer shell and the screening of the (Zn,Pb)S shell of the inner layers from the penetration of exciting radiation.

The Application of Spectral Luminescent Method to Examine Alcohol-Containing Liquids Produced Using Rectified Ethyl Alcohol

The possibility to apply the spectral-luminescent method using spectrophotometer Specord M40 with the attachment for fluorescence measuring to determine the nature of the basic alcohol in liquids produced using rectified ethyl alcohol has been considered. The analysis of model mixtures of aromatic amino acids (tryptophan, tyrosine, phenylalanine) has been performed to determine the characteristic bands in the luminescence excitation spectrum. The parameters of an adapted method for determining the nature of the basic alcohol (from food or non-food raw materials) of a liquid by comparative research of known spectrum of Lux ethyl rectified alcohol from food raw materials have been justified. The reasons limiting the application of the method have been analyzed: it is shown that the presence of food additives and flavors containing phenolic groups used in recipes of alcoholcontaining liquids can influence the luminescence of the basic alcohol significantly and, consequently, the identification result for the nature of the alcohol.

Facile Synthesis of CaCo3 and CaCo3:Eu3+ Phosphors by Solid State Reaction at Room Temperature and the Luminescence Properties

The CaCO3 and CaCO3:Eu3+ phosphors have been synthesized by solid state reaction at room temperature without further sintering treatment. The morphology, crystalline structure, and fluorescent properties of the samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), spectrofluorometer, respectively. Also, the influences of Eu3+-doping concentration on the photoluminescence (PL) properties were investigated in detail. The results indicate that the morphology of as-prepared CaCO3 particles are irregular cubic in shape and about 200-400nm in size, while the CaCO3:Eu3+ particles are the aggregates of many small nanoparticles with nearly 30nm in size, indicating that Eu3+ ions have a great influence on the CaCO3 particle morphology and size. The lines around 392nm in luminescence excitation spectrum is the most noticeable. Upon excitation at 392nm, the PL emission spectrum is composed of two band and strong peaks at 589nm and at 613nm. The peaks at 589nm is attributed to magnetic dipole transition 5D0–7F1 and with the increase of the Eu3+-doped concentration, the intensity decreases gradually; but it shows the opposite trend for the peak at 613nm which is attributed to the hyper sensitively forced electric dipole transition5D0–7F2.

The Influence of Mechanical Deformation on the Optical Properties of Laminated As2S3, GeSe2 and As2Se3 Crystals

Reversible photostructural conversions (darkening and bleaching) attended by a shift of transmittance edge and by the photoluminescence fatigue effect are revealed. Upon mechanical treatment of crystals the maximum of the luminescence excitation spectrum shifts toward higher energies. The low-energy edge of the luminescence spectrum flattens, and emission intensity increases. The experimental results are interpreted within a configuration model of two stable structural states of molecular groups.