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35 results on '"Hájek, František"'

1. On the origin of the light yield enhancement in polymeric composite scintillators loaded with dense nanoparticles

Author

Villa, Irene, Monguzzi, Angelo, Lorenzi, Roberto, Orfano, Matteo, Babin, Vladimir, Hájek, František, Kuldová, Karla, Kučerková, Romana, Beitlerová, Alena, Mattei, Ilaria, Buresova, Hana, Pjatkan, Radek, Čuba, Václav, Procházková, Lenka Prouzová, and Nikl, Martin

Subjects
Physics - Instrumentation and Detectors, Condensed Matter - Materials Science
Abstract

Fast emitting polymeric scintillators are requested in advanced applications where high-speed detectors with large signal-to-noise ratio are needed. However, their low density implies a weak stopping power of high energy radiations, thus a limited light output and sensitivity. To enhance their performances, polymeric scintillators can be loaded with dense nanoparticles (NPs). We investigate the properties of a series of polymeric scintillators by means of photoluminescence and scintillation spectroscopy, comparing standard scintillators with a composite system loaded with dense hafnium dioxide (HfO2) NPs. The nanocomposite shows a scintillation yield enhancement of +100% with unchanged time response. We provide for the first time an interpretation of this effect, pointing out the local effect of NPs in the generation of emissive states upon interaction with the ionizing radiation. The obtained results indicate that coupling of fast conjugated emitters with optically inert dense NPs could allow to surpass the actual limits of pure polymeric scintillators., Comment: 14 pages, 4 figures

Published
2024

8. High-κ Wide-Gap Layered Dielectric for Two-Dimensional van der Waals Heterostructures

Author

Söll, Aljoscha, primary, Lopriore, Edoardo, additional, Ottesen, Asmund, additional, Luxa, Jan, additional, Pasquale, Gabriele, additional, Sturala, Jiri, additional, Hájek, František, additional, Jarý, Vítězslav, additional, Sedmidubský, David, additional, Mosina, Kseniia, additional, Sokolović, Igor, additional, Rasouli, Saeed, additional, Grasser, Tibor, additional, Diebold, Ulrike, additional, Kis, Andras, additional, and Sofer, Zdeněk, additional

Published
2024
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12. Donor-Acceptor Pairs Recombination as the Origin of the Emission Shift In InGaN/GaN Scintillator Heterostructures Doped with Zn

Author

Hájek, František, primary, Jarý, Vítězslav, additional, Hubáček, Tomáš, additional, Dominec, Filip, additional, Hospodková, Alice, additional, Kuldová, Karla, additional, Oswald, Jiří, additional, Pangrác, Jiří, additional, Vaněk, Tomáš, additional, Buryi, Maksym, additional, Ledoux, Gilles, additional, and Dujardin, Christophe, additional

Published
2023
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16. Relation between Ga Vacancies, Photoluminescence, and Growth Conditions of MOVPE-Prepared GaN Layers

Author

Hospodková, Alice, primary, Čížek, Jakub, additional, Hájek, František, additional, Hubáček, Tomáš, additional, Pangrác, Jiří, additional, Dominec, Filip, additional, Kuldová, Karla, additional, Batysta, Jan, additional, Liedke, Maciej O., additional, Hirschmann, Eric, additional, Butterling, Maik, additional, and Wagner, Andreas, additional

Published
2022
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19. Untangling the controversy on Ce3+ luminescence in LaAlO3 crystals

Author

Pejchal, Jan, primary, Babin, Vladimir, additional, Buryi, Maksym, additional, Laguta, Valentyn, additional, Hájek, František, additional, Páterek, Juraj, additional, Procházková-Prouzová, Lenka, additional, Havlák, Lubomír, additional, Czerneková, Vladimíra, additional, Vaněček, Vojtěch, additional, Doležal, Václav, additional, Havlíček, Jan, additional, Rubešová, Kateřina, additional, Zemenová, Petra, additional, Falvey, Alexandra, additional, Král, Robert, additional, Pankratov, Vladimir, additional, and Chernenko, Kirill, additional

Published
2022
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21. The Effect of Be Co‐Doping on Luminescence Properties of Gd3Al3Ga2O12:Ce Glass Ceramics.

Author

Tratsiak, Yauhen, Trusova, Ekateryna, Buryi, Maksym, Babin, Vladimir, Dominec, Filip, Hájek, František, and Malashkevich, Georgii

Subjects
LUMINESCENCE, GADOLINIUM, CERAMICS, RADIOLUMINESCENCE, GLASS, ELECTRON traps
Abstract

The glass‐ceramics (GC) of gadolinium aluminum gallium garnets with the expected composition of Gd3Al3Ga2O12:Ce and Gd3Al3Ga2O12:Ce,Be (GAGG:Ce and GAGG:Ce,Be, respectively) are fabricated by crystallization from the Gd2O3–Al2O3–Ga2O3–CeO2–SiO2–BeO (Gd:Ga:Al ratio is close to 3:2:3) glasses. The influence of Be2+ co‐doping (including doping level) on the luminescent properties of the GAGG is demonstrated. In particular, Be co‐doping results in the suppression of the Ce3+‐related radioluminescence (RL) and as a consequence, the light yield is lowered as well. The conclusion is made that Be2+ creates effective electron or hole trapping centers. [ABSTRACT FROM AUTHOR]

Published
2022
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26. Advancement toward ultra-thick and bright InGaN/GaN structures with a high number of QWs

Author

Hubáček, Tomáš, primary, Hospodková, Alice, additional, Kuldová, Karla, additional, Oswald, Jiří, additional, Pangrác, Jiří, additional, Jarý, Vitězslav, additional, Dominec, Filip, additional, Slavická Zíková, Markéta, additional, Hájek, František, additional, Hulicius, Eduard, additional, Vetushka, Alexej, additional, Ledoux, Gilles, additional, Dujardin, Christophe, additional, and Nikl, Martin, additional

Published
2019
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28. Studie možnosti ovlivnění procesu transformace primární organické hmoty v kompostu ionty Ca+2 a Mg+2

Author

HÁJEK, František

Subjects
cation exchange capacity, půdní organická hmota, quantity, composting, kompost, kvalita, kvantita, humic substances, kationtová výměnná kapacita, humus, urychlovač do kompostů, topsoil, compost akcelerátor, quality, soil organic matter, humusové kyseliny
Abstract

This study focuses on the entire proces of composting. It begins with listing the attributes of entry materials and spans to outlining the creation of characteristic substances in the compost (humus). Problems and solutions relating to determining the quality and quantity of humus in the compost are elaborated. This thesis was designed to identify efficient compost accelerator additives for gardening composts.

Published
2017

31. Compost accelerator to composters and garden composts

Author

HÁJEK, František

Subjects
urychlovač kompostérů, kompost, cation exchange capacity, compost, topsoil, kationtová výměnná kapacita, humus, compost accelerator
Abstract

The purpose of this paper is to research and suggest good-quality compost accelerators that could be effectively used in the garden composts. The additive eliminates the shortage of the input pulverized grass matter which is being composted. This thesis also describes the features of the compost, the nature of the correct composting procedures, and the legal implications to the production of the composting process. This paper elaborates the efficiency of the compost accelerators that are available within the home market and abroad. An important component of my accelerator is magnesium from the Dolomites limestone distributed by the "HASIT" company which positively affects the process of humification. The experiment of compostation with this type of accelerator took place on the pulverized grass matter. In order to objectively assess the quality of the composts, the Sanhoff´s method of stating the cation exchange capacity was used. During this experiment, the cation exchange capacity increased by 22% in the sample where the accelerator has been used, as compared to the sample where only the composted grass matter was present. Based on the results gathered, it is feasible to conclude that the suggested accelerator does have a significant impact on the composting of the grass matter. Due to this fact, it is strongly recommended to conduct a further research on the composition of the compost accelerators.

Published
2015

32. Heavily Ce3+-doped Y3Al5O12 thin films deposited by a polymer sol–gel method for fast scintillation detectors.

Author

Rubešová, Kateřina, Havlíček, Jan, Jakeš, Vít, Nádherný, Ladislav, Cajzl, Jakub, Pánek, Dalibor, Parkman, Tomáš, Beitlerova, Alena, Kučerková, Romana, Hájek, František, and Nikl, Martin

Subjects
SCINTILLATION counters, THIN films, SOL-gel processes, POLYMER colloids, POLYMER films, SINGLE crystals, SOFT X rays
Abstract

The performance of cerium-doped Y3Al5O12 (Ce3+:YAG) often depends on cerium solubility achievable in a particular preparation technology. This solubility is kinetically affected by the synthesis process which allows for Ce3+ solubility to be generally much higher in a polycrystalline material than in single crystals. This work presents Y3−xCexAl5O12 polycrystalline thin films deposited by spin-coating where cerium is substituted on yttrium sites in an interval of 3.3–25 at%. Up to a concentration of 18 at%, the samples remain single-phase, which is the highest Ce3+ doping level in YAG published so far. Absorption, excitation and emission photoluminescence spectra are presented. The photoluminescence decays of the samples containing up to 6 at% cerium are comparable in radiative lifetime to those of Ce3+:YAG single crystals having the cerium concentration limit over one order smaller. The cathodoluminescence of the samples and soft X-ray nanosecond pulse-excited decays are examined. The scintillation decays appear much faster with a 1/e decay time well below 10 ns compared to that of a Ce3+:YAG single crystal which is 140 ns. After further optimization of the microstructure and the overall scintillation yield, sol–gel prepared Ce3+:YAG thin films are promising candidates for application in fast SEM scintillation detectors, currently intensively investigated in the scintillator technology field. [ABSTRACT FROM AUTHOR]

Published
2019
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33. The Effect of Be Co‐Doping on Luminescence Properties of Gd3Al3Ga2O12:Ce Glass Ceramics

Author

Tratsiak, Yauhen, Trusova, Ekateryna, Buryi, Maksym, Babin, Vladimir, Dominec, Filip, Hájek, František, and Malashkevich, Georgii

Abstract

The glass‐ceramics (GC) of gadolinium aluminum gallium garnets with the expected composition of Gd3Al3Ga2O12:Ce and Gd3Al3Ga2O12:Ce,Be (GAGG:Ce and GAGG:Ce,Be, respectively) are fabricated by crystallization from the Gd2O3–Al2O3–Ga2O3–CeO2–SiO2–BeO (Gd:Ga:Al ratio is close to 3:2:3) glasses. The influence of Be2+co‐doping (including doping level) on the luminescent properties of the GAGG is demonstrated. In particular, Be co‐doping results in the suppression of the Ce3+‐related radioluminescence (RL) and as a consequence, the light yield is lowered as well. The conclusion is made that Be2+creates effective electron or hole trapping centers. The article is about the glass‐ceramics form of Gd3Al3Ga2O12:Ce and Gd3Al3Ga2O12:Ce,Be, gadolinium aluminum gallium garnets. Be2+co‐doping affects the luminescent properties of Ce3+in these materials by the suppression of light yield. Moreover, the decay time of the photoluminescence (PL) decreases upon beryllium content. These observations lead to the conclusion of the effective beryllium‐based charge trapping centers’ existence.

Published
2022
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34. Scintillation Response Enhancement in Nanocrystalline Lead Halide Perovskite Thin Films on Scintillating Wafers.

Author

Děcká, Kateřina, Král, Jan, Hájek, František, Průša, Petr, Babin, Vladimir, Mihóková, Eva, and Čuba, Václav

Subjects
THIN films, PEROVSKITE, LEAD halides, POSITRON emission tomography, COMPOSITE materials, RADIOLUMINESCENCE
Abstract

Lead halide perovskite nanocrystals of the formula CsPbBr3 have recently been identified as potential time taggers in scintillating heterostructures for time-of-flight positron emission tomography (TOF-PET) imaging thanks to their ultrafast decay kinetics. This study investigates the potential of this material experimentally. We fabricated CsPbBr3 thin films on scintillating GGAG:Ce (Gd2.985Ce0.015Ga2.7Al2.3O12) wafer as a model structure for the future sampling detector geometry. We focused this study on the radioluminescence (RL) response of this composite material. We compare the results of two spin-coating methods, namely the static and the dynamic process, for the thin film preparation. We demonstrated enhanced RL intensity of both CsPbBr3 and GGAG:Ce scintillating constituents of a composite material. This synergic effect arises in both the RL spectra and decays, including decays in the short time window (50 ns). Consequently, this study confirms the applicability of CsPbBr3 nanocrystals as efficient time taggers for ultrafast timing applications, such as TOF-PET. [ABSTRACT FROM AUTHOR]

Published
2022
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35. On the Origin of the Light Yield Enhancement in Polymeric Composite Scintillators Loaded with Dense Nanoparticles.

Author

Villa I, Monguzzi A, Lorenzi R, Orfano M, Babin V, Hájek F, Kuldová K, Kučerková R, Beitlerová A, Mattei I, Buresova H, Pjatkan R, Čuba V, Prouzová Procházková L, and Nikl M

Abstract

Fast emitting polymeric scintillators are requested in advanced applications where high speed detectors with a large signal-to-noise ratio are needed. However, their low density implies a weak stopping power of high energy radiation and thus a limited light output and sensitivity. To enhance their performance, polymeric scintillators can be loaded with dense nanoparticles (NPs). We investigate the properties of a series of polymeric scintillators by means of photoluminescence and scintillation spectroscopy, comparing standard scintillators with a composite system loaded with dense hafnium dioxide (HfO 2 ) NPs. The nanocomposite shows a scintillation yield enhancement of +100% with an unchanged time response. We provide for the first time an interpretation of this effect, pointing out the local effect of NPs in the generation of emissive states upon interaction with ionizing radiation. The obtained results indicate that coupling fast conjugated emitters with optically inert dense NPs could lead to surpassing the actual limits of pure polymeric scintillators.

Published
2024
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