National Repository of Grey Literature 71 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Optimization of the operational temperature of photoluminescence sensor field for detection of linear alcohols
Pokorný, Matěj ; Dian, Juraj (advisor) ; Červený, Václav (referee)
Chemical sensors are used to detect the presence of chemical substances using various physical quantities. Porous silicon, prepared by electrochemically etching the surface of crystalline silicon with a mixture of hydrofluoric acid and ethanol under appropriate conditions, is a porous material that contains nanocrystalline forms of silicon. Nanocrystalline silicon exhibits intense photoluminescence properties at room temperature, which strongly depend on the presence of chemical substances in its surroundings. The photoluminescence intensity of porous silicon is generally quenched in the presence of the analyte. The photoluminescence sensor response to the substances to be determined depends mainly on the concentration of the substance in question, but also on the operating conditions. Most critical is the operating temperature, which fundamentally affects the intensity of photoluminescence and the rate of sensor response when the analyte is added or removed from the system. The aim of this bachelor thesis was the preparation of porous silicon samples and their characterization by infrared (FTIR) and photoluminescence spectroscopy. These samples were tested as sensor elements of a photoluminescence sensor array for the detection of ethanol linear alcohol vapor. The main objective of the bachelor...
Near-field excited photoluminescence mapping
Klok, Pavel ; Ledinský, Martin (referee) ; Dvořák, Petr (advisor)
Tato práce se zabývá mapováním fotoluminiscence (PL) pomocí buzení blízkého pole (NF), které slouží ke zkoumání optoelektronických vlastností v nanometrovém měřítku. Díky překonání omezení tradičních optických technik v dalekém poli zkoumá jevy na menších rozměrech, které by jinak byly nedostupné. Hlavní důraz je kladen na NF rastrovací optickou mikroskopii, která umožňuje pozorování poddifrakčních jevů u studovaných vzorků. Významným přínosem této práce je zavedení časově rozlišitelného mapování PL v NF, tedy průlomové metody pro studium dynamických procesů pod hranicí difrakce. Tento přístup představuje nový přínos pro tento obor, což potvrzuje i přehled literatury uvedený v této práci. Díky pečlivému vyhodnocení a interpretaci měření PL tato práce rozšiřuje naše znalosti o optických vlastnostech olovnatých halogenidových perovskitů a jejich potenciálních aplikacích např. pro solární články. Dále odhaluje dosud neprozkoumané možnosti v oblasti časově rozlišitelného mapování PL v NF a poskytuje dosud nevídaný náhled do dynamických procesů pod difrakčním limitem. Posunutím hranic optického výzkumu na úrovni nanorozměrů vytváří tato diplomová práce základ pro nové směry zkoumání v této oblasti.
Ceramic materials based on spinel MgAl2O4 for optical applications
Rychnovský, Daniel ; Maca, Karel (referee) ; Drdlík, Daniel (advisor)
This diploma thesis deals with preparation of transparent ceramics based on spinel MgAl2O4 and effect of Cr3+, Tb3+ doping on optical properties. Preparation of samples was optimized using several ways to prepare non-defect ceramic samples with the highest relative density of green body. The final step of the processing included hot isostatic pressing resulting in transparent undoped and doped spinel ceramics. The highest values of RIT (real in- line transmittance) of undoped and doped samples were measured between 77–79 %. It was found by measuring photoluminescence properties of prepared samples that increasing concentration of Cr3+ resulted to higher peak intensities. The most intense emission peak was measured in red spectral area at wavelength of 685 nm. In the case of Tb3+-doped spinel, the maximum peak intensities were measured at concentration of 0.075 at. % and the most intense emission peak was measured in green spectral area at wavelength of 545 nm.
Porous silicon based optical sensors of chemical species for gas phase
Liška, Jiří ; Dian, Juraj (advisor) ; Červený, Václav (referee)
Title: Porous silicon-based optical sensors of chemical species for gas phase Author: Bc. Jiří Liška Department: Department of Inorganic Chemistry Supervisor: doc. RNDr. Juraj Dian, CSc. Abstract: Porous silicon is a nanostructured material, which is a suitable material for che- mical sensors due to its optical properties, especially photoluminescence and its quenching depending on the chemicals in the environment. Optical sensors based on porous silicon are the most studied group of sensors and have been successfully used for the detection of chemicals in both liquid and gas phases. In addition, the surface of porous silicon can be modified by a number of techniques, thereby modifying the recognition properties. In the case of combining multiple sensor elements of different properties, it is possible to measure multiple responses in the photoluminescent sensor array. The objectives of this thesis are: 1. Extension of electrochemical characterisation of initial silicon substrates using vol- tammetric techniques under different lighting conditions during the experiment, preparation of porous silicon samples from different types of crystalline silicon sub- strates (p-type, n-type), crystallographic orientation and doping degree. 2. Functionalisation of porous silicon surface with new chemical compounds by...
Emergence of dark ZnO nanorods by hydrogen plasma treatment
Remeš, Zdeněk ; Buryi, Maksym ; Sharma, Dhananjay K. ; Artemenko, Anna ; Mičová, J. ; Rezek, B. ; Poruba, A. ; Hsu, H.S. ; Potocký, Štěpán ; Babin, Vladimir
We employed a custom-built inductively coupled plasma (ICP) 13.56 MHz reactor with up to 300 W RF discharge power. Hydrothermally grown ZnO nanorods were exposed to the ICP plasma with a mixture of hydrogen and argon for up to 30 min, followed in-situ by plasma oxidation. Plasma properties were monitored by optical emission spectroscopy (OES) and by measuring the self-bias potential of the stainless steel sample holder separated from the ground by a blocking capacitor. The exciton-related UV photoluminescence of ZnO nanorods and optical absorption increases significantly after the plasma treatment. We attribute it to the complex changes of ZnO surface electronic states that also give rise to its black color visually.
Automatization of experimental setup for optical spectroscopy
Čecháček, Jan ; Nováček, Zdeněk (referee) ; Dvořák, Petr (advisor)
This bachelor thesis deals with the modernization and improvement of an application that automates measurements on an experimental setup for spectral and topographic mapping using confocal microscopy and near-field microscopy. The arrangement of the report, the principle of communication of the program with individual parts of the report and the principle of data collection and processing are described here. The output of the program are point spectra and 2D maps describing the topography, intensity and position of the spectral peaks. The thesis includes a research study of optical and time-resolving optical spectroscopy and their applications in nanophotonics. The correct functionality of the program is demonstrated by the results of measurements of perovskite MAPbI3 and organic substrate.
Optical characterization of perovskite nanostructures
Urban, Jakub ; Kvapil, Michal (referee) ; Dvořák, Petr (advisor)
The present bachelor's thesis focuses on the optical characterization of CsPbBr3 nanocrystals ranking among the group of materials called perovskites which are remarkable for their high photoluminescence (PL) quantum yield. An algorithm for a correlation of experimental data measured by PL mapping with morphological and topological properties obtained by using Scanning Electron Microscopy and Atomic Force Microscopy has been developed which clears the way for a particular crystal detection and their spectrum analysis. Specifically, crystals the shape of which can be approximated by a cuboid have been detected and the volume dependence of the centre of mass of their PL, which is proportional to V^(-2/3) as predicted by the theorethical model, has been discovered. The measurement of PL dependency on temperatures ranging from 40 to 60 °C has also been conducted and in this temperature interval linear dependence of the full width at half maximum of their PL spectral line that rises with rising temperature has been confirmed. On the contrary, the centre of mass of PL has been found to be temperature independent.
Photoluminescence of CdTe crystals
Procházka, Jan ; Hlídek, Pavel (advisor) ; Toušek, Jiří (referee) ; Oswald, Jiří (referee)
Title: Photoluminescence of CdTe crystals Author: Jan Procházka Department: Institute of Physics of Charles University in Prague Supervisor: Doc. RNDr. Pavel Hlídek, CSc. Abstract: Energy levels connected with defects in nominally undoped crystals CdTe, indium- doped crystals and chlorine-doped crystals were studied using low-temperature photoluminescence. The crystals are intended for X- and gamma- ray detectors operated at room temperature. An effect of annealing in cadmium or tellurium vapor on luminescence spectra was investigated. Some changes were interpreted by filling of vacancies not only by atoms coming from gaseous phase but also by impurities from defects like interstitials, precipitates, inclusions, grain boundaries etc. The luminescence bands assigned to defects important for compensation mechanism were examined, namely A-centers (complexes of vacancy in cadmium sublattice and impurity shallow donor) and complexes of two donors bound to a vacancy. It was shown, that temperature dependence of the luminescence bands results from more complicated processes than a simple thermal escape of bound excitons or thermal excitation of electrons (holes) from defects to bands. We observed expressive "selective pair luminescence" bands (SPL) on partially compensated In-doped samples during sub-gap...
Reversible interactions of pyrazines and photoluminescent dihydropyrazines
Coufal, Radek ; Drahoňovský, Dušan (advisor) ; Roithová, Jana (referee)
This thesis deals with two independent topics. The first is focused on the study of reversible covalent interactions of a carbonyl group with alcohols and water forming hemiacetals (respectively hydrate) derived from pyrazine trifluormethylketone. The main research method in this part is the NMR spectroscopy and experimental results are also supported by quantum chemical calculations. The second topic aims to the preparation and the study of photochemical properties of three dihydropyrazines which exhibit fluorescence both in solution and solid phase. The fluorescence can be influenced by means of complexation by various metal ions. Prepared dihydropyrazines also show interesting values of the Stokes shift. The structure of these new compounds was confirmed by X-ray analysis.
Centra rekombinace v semiizolačním CdTe
Zázvorka, Jakub ; Franc, Jan (advisor) ; Fiederle, Michael (referee)
Title: Recombination centers in semiinsulating CdTe Author: Jakub Zázvorka Department / Institute: Institute of Physics of Charles University Supervisor of the master thesis: prof. Ing. Jan Franc, DrSc., Institute of Physics of Charles University Abstract: The properties of CdTe for application as a radiation detector are influenced through the presence of deep levels in the bang gap. These energy levels complicate the charge collection and the detector efficiency. Contactless resistivity mapping (COREMA) represents a good option for material characterization without the necessity of metal contacts application. The time-dependent charge measurement was investigated on an adjusted apparatus in FMF Freiburg. Theoretical model of charge transport based on band bending on the sample surface was proposed and a non-exponential behavior was calculated. Using this, the resulted parameter tendencies and their connection with deep level trap or recombination center were explained. A correlation was observed between resistivity, photoconductivity and a near midgap level photoluminescence. Parameter profiles were explained using the theory of Fermi level shift relative to the near midgap level. Three deep levels were observed on samples grown at the Charles University in Prague. Their photoluminescence supports the...

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