Novel SnO₂ based optical sensor for detectin of low ammonia concentration in water at room temperatures

In the work, presented are preliminary experimental results on the capability of a metal oxide (MO) based optical sensor to perform ammonia detection in water environment at room temperature. The electro-spray pyrolysis technique was used to deposit SnO₂ films on the distant end of standard silica optical fiber (SOF). Reflection spectra of the studied samples were preliminarily characterized in the range of 1520 to 1620 nm by using a tunable laser and an optical spectrum analyzer. Single wavelength reflectance measurements were carried out to test the sensing performances for detecting the ammonia of concentration from 4 to 20 ppm. High sensitivity to the target analyte and fast response times were observed. From the results obtained, the detection limit close to a sub-ppm level was achieved

Optical and electrical properties of Zn1-xBexSe grown by molecular beam epitaxy

Journal of Physical Studies, 8(4): pp. 384–388. Retrieved September 19, 2006 from http://www.ece.drexel.edu/mml/pubs/jps_paper.pdfThe dopant behaviour in the n-type ZnBeSe:Cl and p-type ZnBeSe:N grown by Molecular Beam Epitaxy (MBE) is investigated. All the samples have been grown on (001) GaAs substrates (conducting or semi-insulating). For the experimental investigation the photoluminescence (PL), Raman Scattering, photoconductivity and I–V measurements are used. From the temperature (9 K–300 K) and exitation intensity dependent on PL measurements it will be shown that donor and acceptor impurities exhibit a somewhat different behaviour and/or properties from those in ZnSe. We argue that (i) the activation energy of both the N acceptor and Cl donor increases in ZnBeSe as concentration of Be increases; (ii) all the indoped and n-type samples exhibit high (>180 K) temperature PL associated with shallow impurity of acceptor type, which also show an increase in the binding energy with Be composition; Raman scattering experiments have shown that at low Be concentrations (x < 0.04) one can use LO photon energy in ZnSe in the analyses of PL spectra from ZnBeSe. From photoconductivity and I–V measurements we show that (i) there are a number of carrier traps in ZnBeSe:Cl; (ii) some of the ZnBeSe samples with Be concentrations over 1% exhibit photoconductivity behaviour associated with the presence of DX centres or other deep trap, i. e., we observe persistent photoconductivity; (iii) volt-ampere dependencies (with and without irradiation) are different for the samples grown on conducting and semi-insulating substrates

Theory of cultural resilience as an instrument for interpretation of cultural changes in North-Western Black Sea region on the Pleistocene-Holocene boundary under the global climate change

Рассматривается теория упругости культуры как инструмент интерпретации культурных изменений в Северо-Западном Причерноморье на рубеже плейстоцена и голоцена под влиянием глобальных изменений климата.This article summarizes the contemporary postulates of the cultural resilience theory and examines the possibility of its application for the studies of human response to the global climate change in the Early Prehistoric societies. Evolution of the subject field of the resilience concept is demonstrated through the broad range of natural, social and environmental sciences. Subject of special attention of the author is the essence of cultural resilience notion and its application in the prehistoric studies, particularly, for the hunter-gatherers societies. The article particularly focuses on the transformation of livelihood and subsistence strategy of the population of the North-Western Black sea region which took place on the Pleistocene-Holocene boundary in connection with the Black Sea level rise and the coastline migration and possibility of its further explanation on the base of the cultural resilience theory. As the result, the culture resilience theory is conceptualized as an important component of the contemporary methodology of the conceptualization of human and nature interaction in historical retrospection, applied for explanation of the durability and the scale of changes in the mode of life, subsistence strategy and social networking background. In this context the special emphasis in the cultural resilience studies should be made on the everyday routine activities of prehistoric population, which helped this cultural group to survive without any principal transformations

MODELLING OF RAPID STAGE DECAY OF SIGNAL OF OPTICAL SENSOR BASED ON HETEROSTRUCTURE CdS-Cu2 S

The work is devoted to modeling and calculation of the spatial distribution of the concentration of charge localized in the space charge region (SCR) heterojunction, this distribution changes with time at different initial filling of deep traps centers nonequilibrium holes. Within the framework described model the theoretical calculation of two characteristic stages of relaxation current, compliance with the calculated and experimentally obtained dependencies was demonstrated

Synthesis of CdS Nanocrystalsin the Gelatin Matrix with Different рН Values and their Optical Properties

We have investigated the influence of solution pH on the formation of nanocrystals and their size in the process of synthesis. We have analyzed the optical absorption spectra and luminescence of colloidal solutions of NC CdS.Nanocrystals of cadmiumsulphide were obtained by sol-gel technology in gelatin solution which has different pH values (6 ÷ 10). A decrease was observed in the average size of the nanocrystals from 8 till 3.5 nm while reducing pH from 10 to 6. There has been established the dependence of the contour of luminescence spectra from pH values

Method of infrared radiation detection by uncooled photodetector

The article describes an optical method for detecting radiation in the far infrared region of the spectrum against the thermal noise background with an uncooled photodetector (PD) that is relevant for the field of indicator sensors. The basis of the PD is an abrupt anisotype heterojunction, made according to the “optical window–absorber” connection. The article considers the mechanism of the appearance of photocurrent components in a heterojunction during the absorption of long-wave radiation and their ratio. A measurement of the photocurrent in PD by incorporating a heterojunction into a bridge circuit is proposed. An analytical description of the dependence of the loop currents on the elements of the equivalent heterojunction circuit and the bridge measurement circuit is given. It is established that the functional dependences of the photocurrent components through the structural elements of the heterojunction are opposite in sign and intersect at the point of equality of their values. The method makes it possible to divide the currents in the heterojunction layers, calculate or set the current reference value by adjusting the measuring circuit and to provide the measurement of the photocurrent that is less than the thermal background in magnitude. An example of the practical implementation of the method in a heterojunction PD with the structure n(CdSe)–p(Pb1–xSnxSe) is presented

Вплив органічних молекул на люмінісцентні властивості композитів на основі квантових точок CdS

The influence of methylene blue (MB) and acridine yellow (AY) dyes on the spectra of luminescence of CdS with quantum dots (QD) dye composites is investigated. It is shown that the luminescence spectrum of the heterosystem of nanocrystals (NC) CdS – the dye depends on the absorption region of it. The spectrum of the luminescence of the quantum dots is shifted to the red region by the introduction into the colloidal solution of the MB dye and in a case of the insertion of AY the spectrum is shifted into the blue region. The obtained results are explained in a point of view of the transferring the energy from the CdS quantum dots to the dyes by the Forster mechanism.Досліджено вплив барвників метиленового блакитного (МБ) і акридинового жовтого (АЖ) наспектри люмінесценції композитів барвників с квантовыми точками (КТ) CdS. Показано, что спектрлюмінесценції гетеросистеми нанокристалів (НК) CdS - барвник залежить від області поглинаннябарвника. При введенні в колоїдний розчин МБ барвника спектр люмінесценції квантових точокзміщується в червону область, а при введенні АЖ - в блакитну. Отримані результати пояснюються зточки зору передачі енергії від квантових точок CdS до барвників за механізмом Ферстера