scholarly journals Фотолюминесценция квантовых точек (Zn, Pb, Mn)S в полиакрилатной матрице

2020 ◽  
Vol 54 (5) ◽  
pp. 435
Author(s):  
А.А. Исаева ◽  
В.П. Смагин
Keyword(s):  
Glassy State ◽  
Electron Transition ◽  
Thermal Polymerization ◽  
Exciting Radiation ◽  
Colloidal Synthesis ◽  
Molar Ratio ◽  
Interband Transitions ◽  
Colloidal Solutions ◽  
Electron Recombination ◽  
Absorbing Layer

Solutions of quantum dots (Zn,Pb,Mn)S with different mole ratio of cations were obtained by colloidal synthesis in methyl methacrylate (MMA) medium. By thermal polymerization of MMA in the block, colloidal solutions are transferred to the glassy state. The optical transparency of PMMA/(Zn,Pb,Mn)S compositions at wavelengths >500 nm reaches 90% with the thickness of the absorbing layer up to 5 mm. Photoluminescence of compositions in the spectral region of 400–480 nm is associated with electron recombination at the levels of defects in the crystal structure of ZnS, in the range of 520–620 nm with 4T1 → 6A1 electron transition in Mn2+ ions. Excitation of photoluminescence occurs as a result of interband transitions in ZnS and energy transfer from the conduction band of ZnS to Mn2+ ion levels. The luminescence spectrum depends on the molar ratio of Mn2+ and Pb2+ ions, the sequence of introduction of the components into the reaction mixture, the wavelength of the exciting radiation.

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

2020 ◽  
Vol 63 (11) ◽  
pp. 82-87
Author(s):  
Anastasya A. Isaeva ◽  
Vladimir P. Smagin
Keyword(s):  
Methyl Methacrylate ◽  
Crystal Lattice ◽  
Glassy State ◽  
Luminescence Excitation Spectrum ◽  
Lead Ions ◽  
Structural Defects ◽  
Colloidal Synthesis ◽  
Luminescence Spectra ◽  
Colloidal Solutions ◽  
Poly Methyl Methacrylate

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.

scholarly journals Synthesis and characterization of poly(1-methyltrimethylene carbonate) (PMTMC) by mean ring-opening polymerization

2020 ◽  
Vol 5 (3) ◽  
pp. 21
Author(s):  
Jesús Miguel Contreras Ramírez ◽  
Meribary Monsalve
Keyword(s):  
Ring Opening ◽  
Molar Mass ◽  
Thermal Polymerization ◽  
Ring Opening Polymerization ◽  
Active Species ◽  
Size Exclusion ◽  
Polymerization Process ◽  
Molar Ratio ◽  
Molecular Characteristics ◽  
Ft Ir

  In this work, the activity of samarium (III) acetate (Sm(OAc)3) was evaluated as a possible initiator in the ring opening polymerization (ROP) of 1-methyltrimethylene carbonate (MTMC). The effects of temperature (Tr) and monomer-initiator molar ratio (M/I) on the molecular characteristics (conversion, dispersity, and molar mass) of the polymers obtained were analyzed. The reaction temperature was varied between 90 and 160 °C and the molar ratio M/I between 200 and 1000. The molar mass of the products was obtained by size exclusion chromatography (SEC), while its structure was analyzed using FT-IR and 1H-NMR spectroscopy. Thermal polymerization experiments (in the absence of an initiator) were performed in order to evaluate the effectiveness of the initiator. The comparison between the thermal polymerization of MTMC and its polymerization in the presence of Sm(OAc)3, suggests that acetate has very low catalytic activity as the initiator of the ROP of PMTMC. The molar masses of the polymers obtained ranged between 6000 and 10000 Dalton, and the monomer to polymer conversions varied between 9 and 30 %. SEC chromatograms showed monomodal and symmetric curves, suggesting that only one type of active species participates in the polymerization process. Based on the structural analysis, a polymerization mechanism was proposed in which the water possibly acts as the only active species that initiates the reaction.   Palabra clave: Samarium (III) acetate, ring-opening polymerization, 1-methyltrimethylenecarbonate, poly(1-methyltrimethylenecarbonate).   Abstract En este trabajo se evaluó la actividad del acetato de samario (III) (Sm(OAc)3) como posible iniciador en la polimerización de apertura de anillo (PAA) del carbonato de 1-metiltrimetileno (MTMC). Se analizaron los efectos de la temperatura (Tr) y relación molar monómero-iniciador (M/I) sobre las características moleculares (conversión, dispersidad y masa molar) de los polímeros obtenidos. La temperatura de reacción se varió entre 90 y 160 °C y la relación molar M/I entre 200 y 1000. La masa molar de los productos se obtuvo mediante cromatografía de exclusión por tamaño, mientras que su estructura fue analizada mediante espectroscopia FT-IR y 1H-RMN. Además, se realizaron algunos experimentos de polimerización térmica (en ausencia de iniciador) que sirvieron de referencia para evaluar la efectividad del iniciador. La comparación de los resultados obtenidos en la polimerización térmica y en presencia del Sm(OAc)3 indicó que este último presenta muy poca actividad catalítica como iniciador de la PAA de PMTMC. Las masas molares de los polímeros obtenidos oscilaron entre 6000 y 10000 Dalton, mientras que las conversiones de monómero a polímero variaron entre 9 y 30%. Los cromatogramas SEC mostraron curvas mono-modales y simétricas, indicando que en el proceso de polimerización participa un solo tipo de especie activa. En base al análisis estructural, mediante técnicas espectroscópicas, se propuso un mecanismo de reacción para la polimerización en la que el agua posiblemente actúa como la única especie activa iniciadora de la reacción.   Keywords: Acetato de samario (III), polimerización por apertura de anillo, 1-metiltrimetilencarbonato, poli(1-metiltrimetilencarbonato).  

scholarly journals Деградация фотолюминесценции тонких пленок ZnTPP и ZnTPP-C-=SUB=-60-=/SUB=- под действием гамма-облучения

2018 ◽  
Vol 52 (8) ◽  
pp. 931
Author(s):  
Н.М. Романов ◽  
М.А. Елистратова ◽  
E. Lahderanta ◽  
И.Б. Захарова
Keyword(s):  
Composite Films ◽  
Electron Transition ◽  
Radiative Transition ◽  
Dose Dependence ◽  
Threshold Dose ◽  
Nanocomposite Films ◽  
Molar Ratio ◽  
Γ Irradiation ◽  
Hard Radiation ◽  
The Stability

AbstractPorphyrins and their fullerene complexes are promising materials for organic photovoltaic structures. However, the stability of the properties of organic components under hard radiation is poorly studied. Here, the influence of γ irradiation with medium (about 10^4 Gy) and large (10^7 Gy) doses on the photoluminescence of thin structurally perfect films of both pure porphyrin ZnTPP and ZnTPP/C_60 composite films in the molar ratio of 1.3: 1 is investigated. It is shown that the intensity of the electronic radiative transition (626 nm) decreases under the effect of γ irradiation, and the dose dependence is threshold. The threshold dose is ~20 kGy for the ZnTPP films. The intensity of the electron-vibrational part of the spectral dependence of the PL (670–690 nm) for both types of samples decreased at initial irradiation doses and decreases less with a further increase in the irradiation dose than for the purely electron transition. The addition of a fullerene in nanocomposite films increases the threshold dose, after which the PL of the films started to degrade, by a factor of ~2.5. Herewith, the spectral components of the PL associated with the manifestation of the radiation transition of the fullerene C_60 are more stable under γ irradiation.

PHOTOLUMINESCENCE OF NANOCRYSTALLINE CdTe, INTRODUCED INTO POROUS SILICON

2021 ◽  
Vol 56 ◽  
pp. 123-128
Author(s):  
G. A. Pashchenko ◽  
Keyword(s):  
Porous Silicon ◽  
Composite System ◽  
Colloidal Solution ◽  
Mutual Influence ◽  
Planned Change ◽  
Colloidal Synthesis ◽  
Solid Matrix ◽  
Colloidal Solutions ◽  
Cdte Nanoparticles ◽  
The Matrix

A method of colloidal synthesis of monodisperse nanocrystals (NC) with high stability, narrow bands of photoluminescence (PL) and high quantum yield has been developed. The process of colloidal synthesis took place at room temperature and for the passivation of NC used a variety of surfactants. The surface of NC CdTe was modified by introducing them into a matrix, organic or crystalline. In our case, the matrix was porous Silicon (PS), that is a composite structure was formed on the basis of the matrix and NC semiconductor. Nanocomposite structures of PS – NC CdTe were obtained by introducing colloidal solutions of NC CdTe into the solid matrix of PS and subsequent processing at a certain temperature regime. The photoluminescent properties of a composite system in which the matrix is microcrystalline PS and the second component is NC CdTe deposited from a colloidal solution of NC CdTe have been studied. The peculiarity of this system is that both components have PL of different intensities.The large difference in PL intensities and different positions of the radiation bands allowed, comparing the PL spectra of the colloidal solution of NC CdTe, PS and NC CdTe – PS at different stages of introduction of CdTe nanoparticles into the porous Silicon surface, to identify the interaction and mutual influence of the two constituent materials. The main disadvantages of the method are its relative novelty, which leads to the need for empirical selection of some parameters of the synthesis. The planned change of properties of PS and colloidal solutions of NC CdTe by variation of technological methods of synthesis and processing methods will allow to control the physical properties of this composite system and use it to develop new principles of design and creation of new generation sensor devices.

Fe-Doped Graphitic Carbon Nitride for Methylene Blue Degradation with Visible-Light

2021 ◽  
Vol 21 (11) ◽  
pp. 5698-5706
Author(s):  
Mao-Juan Bai ◽  
Xuan-Ye Huang ◽  
Han Yin ◽  
De-Li N¡u ◽  
Jun Wan
Keyword(s):  
Methylene Blue ◽  
Photoelectron Spectroscopy ◽  
Diffuse Reflectance Spectrum ◽  
Synergetic Effect ◽  
Thermal Polymerization ◽  
Molar Ratio ◽  
Doping Amount ◽  
Solution Ph ◽  
Experimental Conditions ◽  
X Ray

In the present work, degradation of methylene blue (MB) dye in aqueous solution through H2O 2and iron doped g-C3N4 (Fe-g-C3N4) was studied. The hybrid was fabricated by thermal polymerization with iron (III) nitrate nonahydrate and melamine, and it was characterized by X-ray diffraction, Fourier transform infrared, UV-Vis diffuse reflectance spectrum, X-ray photoelectron spectroscopy, transmission electron microscope and Brunner-Emmet-Teller. The various experimental conditions such as doping amount, a dose of the sample, solution pH, the addition of H2O2, and concentration of MB on the degradation of MB dye were optimized. The maximum extent of degradation of methylene blue was obtained at pH 5, doping amount of 2.7 wt% and dose of 0.07 g. The molar ratio of Fe:H2O2 is 1:1000 showed 99% of MB (30 mg/L) decolorization over 60 min. The hybrid showed good stability and recyclability after three cycles of use. Photo-Fenton reaction exhibited a higher synergetic effect than the combination of Fenton and photocatalytic process.

Bis(isomaleimide) and diphenol blends: Non-isothermal degradation kinetics and TG-FTIR studies

2018 ◽  
Vol 51 (7-8) ◽  
pp. 644-668
Author(s):  
V Sarannya ◽  
S Shamim Rishwana ◽  
R Mahalakshmy ◽  
A Mahendran ◽  
CT Vijayakumar
Keyword(s):  
Thermal Stability ◽  
Thermal Degradation ◽  
Degradation Products ◽  
Degradation Kinetics ◽  
Thermal Polymerization ◽  
Molar Ratio ◽  
Exponential Factor ◽  
Ftir Studies ◽  
D Values ◽  
Thermal Stability Of

Blends of 4,4′-bisisomaleimidodiphenyl methane (VS) with structurally different diphenols are made in 1:1 molar ratio and thermally polymerized. Thermogravimetric studies of the cured materials show that the thermal stability, the degradation pattern and the char yield are much dependent on the structure of the diphenol that is used for blending. The decreased thermal stability of materials from the blends is attributed to decreased cross links owing to the opening of the isomaleimide rings by diphenols during thermal polymerization. The materials with trimethylphenylindane and tetramethylspirobiindane units exhibit char residue of 21% at 800°C. This is due to the thermal stability of the indane and spirobiindane moieties present in the diphenol molecules. The apparent activation energy for thermal degradation ( Ea-D) and pre-exponential factor (ln A) are derived. The Friedman, corrected Flynn–Wall–Ozawa, corrected Kissinger–Akahira–Sunose and advanced Vyazovkin methods are used to calculate the Ea-D values for various reaction extents ( αs). The Ea-D values of poly(4,4′-bisisomaleimido-diphenyl methane) vary from 168 to 226 kJ mol−1. A slight decrease in Ea-D is noted for the initial α levels and increases constantly up to α = 0.3–0.75 and then the Ea-D values decrease with increasing α values. The highest values of Ea-D and ln A are observed for the polymer derived from the blend of VS with tetramethylspirobiindane diphenol. The volatile products obtained during the thermal degradation of these polymers are analysed using thermogravimetry–Fourier transform infrared (TG-FTIR) spectroscopy. The TG-FTIR studies showed the compounds carbon monoxide, carbon dioxide and aromatic amines are the major degradation products from the polymerized blends.

Production and Annihilation of Triplet Excitons in Organic Materials near Absorbing Surfaces

1971 ◽  
Vol 26 (5) ◽  
pp. 799-802
Author(s):  
H. Kallmann
Keyword(s):  
Energy Transfer ◽  
Exciting Radiation ◽  
Delayed Fluorescence ◽  
Transfer Energy ◽  
Triplet Energy ◽  
Order Of Magnitude ◽  
Absorbing Layer ◽  
Hole Current ◽  
Triplet Energy Transfer ◽  
Triplet Excitons

The theory of delayed fluorescence produced in an organic material by singlet excitation through an absorbing layer is given. It is shown, that it will be reduced by a factor la2/(la +ls)2 due to the singlet energy transfer to such a layer, where U the penetration depth of the exciting irradiation and I3 the diffusion lenght of the singlets. Further reduction of delayed fluorescence should be observed, when also triplet excitons transfer energy to the absorbing layer. Assuming this triplet transfer probability to be of the same order of magnitude as that for triplet energy transfer between neighbouring molecules, it should lead to quenching of delayed fluorescence proportional to la2/lt2 .The exponential portion of the decay of delayed fluorescence should become faster only if triplet energy transfer to the layer takes place. Further, the triplet induced hole-current produced at an absorbing electrode under singlet excitation should display a dependence on the wavelength of the exciting radiation as la(la + ls). Its maximum should not occur at the wavelength of strongest absorption but at much larger penetration depths of the exciting radiation.

Fluorescence effects in quantitative microprobe analysis

1990 ◽  
Vol 48 (2) ◽  
pp. 188-189
Author(s):  
S.J.B. Reed
Keyword(s):  
Microprobe Analysis ◽  
Depth Distribution ◽  
Exciting Radiation ◽  
Primary Radiation ◽  
List Type ◽  
Type Number ◽  
Computing Power ◽  
X Ray ◽  
Fluorescent Radiation

Characteristic fluorescenceThe theory of characteristic fluorescence corrections was first developed by Castaing. The same approach, with an improved expression for the relative primary x-ray intensities of the exciting and excited elements, was used by Reed, who also introduced some simplifications, which may be summarized as follows (with reference to K-K fluorescence, i.e. K radiation of element ‘B’ exciting K radiation of ‘A’):1.The exciting radiation is assumed to be monochromatic, consisting of the Kα line only (neglecting the Kβ line).2.Various parameters are lumped together in a single tabulated function J(A), which is assumed to be independent of B.3.For calculating the absorption of the emerging fluorescent radiation, the depth distribution of the primary radiation B is represented by a simple exponential.These approximations may no longer be justifiable given the much greater computing power now available. For example, the contribution of the Kβ line can easily be calculated separately.

Lipid Polymorphism and Virus-Membrane Fusion as Observed in Vitrified Thin Films by Cryo-Electron Microscopy

1990 ◽  
Vol 48 (1) ◽  
pp. 492-493
Author(s):  
P.M. Frederik ◽  
K.N.J. Burger ◽  
M.C.A. Stuart ◽  
A.J. Verkleij
Keyword(s):  
Electron Microscopy ◽  
Thin Films ◽  
Membrane Fusion ◽  
Film Formation ◽  
Molar Ratio ◽  
Influenza B ◽  
Complex Structures ◽  
Type Ii ◽  
Suspended Material ◽  
Cryo Electron Microscopy

Cellular membranes are often composed of phospholipid mixtures in which one or more components have a tendency to adopt a type II non-bilayer lipid structure such as the inverted hexagonal (H||) phase. The formation of a type II non-bilayer intermediate, the inverted lipid micel is proposed as the initial step in membrane fusion (Verkleij 1984, Siegel, 1986). In the various forms of cellular transport mediated by carrier vesicles (e.g. exocytosis, endocytosis) the regulation of membrane fusion, and hence of inverted lipid micel formation, is of vital importance.We studied the phase behaviour of simple and complex lipid mixtures by cryo-electron microscopy to gain more insight in the ultrastructure of different lipid phases (e.g. Pβ’, Lα, H||) and in the complex membrane structures arising after Lα < - > H|| phase changes (e.g. isotropic, cubic). To prepare hydrated thin films a 700 mesh hexagonal grid (without supporting film) was dipped into and withdrawn from a liposome suspension. The excess fluid was blotted against filter paper and the thin films that form between the bars of the specimen grid were immediately (within 1 second) vitrified by plunging of the carrier grids into ethane cooled to its melting point by liquid nitrogen (Dubochet et al., 1982). Surface active molecules such as phospholipids play an important role in the formation and thinning of these aqueous thin films (Frederik et al., 1989). The formation of two interfacial layers at the air-water interfaces requires transport of surface molecules from the suspension as well as the orientation of these molecules at the interfaces. During the spontaneous thinning of the film the interfaces approach each other, initially driven by capillary forces later by Van der Waals attraction. The process of thinning results in the sorting by size of the suspended material and is also accompanied by a loss of water from the thinner parts of the film. This loss of water may result in the concentration and eventually in partial dehydration of suspended material even if thin films are vitrified within 1 sec after their formation. Film formation and vitrification were initiated at temperatures between 20-60°C by placing die equipment in an incubator provided widi port holes for the necessary manipulations. Unilamellar vesicles were made from dipalmitoyl phosphatidyl choline (DPPC) by an extrusion method and showed a smooth (Lα) or a rippled (PB’.) structure depending on the temperature of the suspensions and the temperature of film formation (50°C resp. 39°C) prior to vitrification. The thermotropic phases of hydrated phospholipids are thus faithfully preserved in vitrified thin films (fig. a,b). Complex structures arose when mixtures of dioleoylphosphatidylethanol-amine (DOPE), dioleoylphosphatidylcholine (DOPC) and cholesterol (molar ratio 3/1/2) are heated and used for thin film formation. The tendency of DOPE to adopt the H|| phase is responsible for the formation of complex structures in this lipid mixture. Isotropic and cubic areas (fig. c,d) having a bilayer structure are found in coexistence with H|| cylinders (fig. e). The formation of interlamellar attachments (ILA’s) as observed in isotropic and cubic structures is also thought to be of importance in biological fusion events. Therefore the study of the fusion activity of influenza B virus with liposomes (DOPE/DOPC/cholesterol/ganglioside in a molar ratio 1/1/2/0.2) was initiated. At neutral pH only adsorption of virus to liposomes was observed whereas 2 minutes after a drop in pH (7.4 - > 5.4) fusion between virus and liposome membranes was demonstrated (fig. f). The micrographs illustrate the exciting potential of cryo-electron microscopy to study lipid-lipid and lipid-protein interactions in hydrated specimens.

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