Raksti konferenču krājumā un tēzes (CFI) / Conference Papers and Abstracts
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- ItemEffect of Yb3+ doping level on the structure and spectroscopic properties of ZnO optical ceramics(Institute of Physics Publishing, 2021) Gorokhova, E.; Venevtsev, I.; Alekseeva, I.; Khubetsov, A.; Dymshits, O.; Basyrova, L.; Oreschenko, E.; Eron’ko, S.; Muktepavela, F.; Kundzins, K.; Zhilin, A.; Loiko, P.Zinc oxide optical ceramics with hexagonal structure doped with 0.6 –5.0 wt% Yb were fabricated by uniaxial hot pressing of commercial oxide powders at 1180 °C in vacuum. The ceramics were characterized by X-ray diffraction, SEM, EDX, X-ray and optical spectroscopy. It is shown that Yb3+ ions are distributed between C-type Yb2O3 sesquioxide crystals and ZnO grain boundaries. The Yb3+ doping of ZnO ceramics enhances the near-band-edge emission of zinc oxide. ZnO:Yb optical ceramics are promising for optoelectronic applications. © 2021 Institute of Physics Publishing. All rights reserved.
- ItemStudies of the possibilities to use ozone for the grain storage(Rezekne Higher Education Institution, 2021) Rucins, Adolfs; Straumite, Evita; Viesturs, Dainis; Kristins, AlbertsIn this study was impact of ozone treatment efficiency of wheat quality (physical-chemical and microbiological parameters, chemical composition and germination rate) during storage analysed. Ozone is a powerful oxidizer, used in processing the agricultural products, including inactivation of pathogens and microorganisms. Investigations in the grain storage by using ozone were performed under farm conditions during two grain storage stages. The first stage – August 2019 – February 2020 and the second stage August 2020 – January 2021. In both stages after harvesting winter wheat yield was 6 t ha-1. Winter wheat was ventilated and then stored for about five months in two identical 20 m3 tanks, with an initial grain layer height of 5.1 m and moisture content the first stage of about 14% and the second stage of about 11% and initial grain mass 17.4 t. At the beginning of the storage period the grain in both tanks was ventilated for 8 hours - in one grain storage tank with the outdoor air, in the other with an ozone supply of 28 mg (m3)-1 in the ventilation air. The grain ventilation and storage process was monitored with a specially designed sensor system; the additional parameters of the process (the grain moisture content, temperature, the ozone concentration) were periodically controlled with hand tools. There were analysed changes of the grain parameters during the storage periods in the ozone-supplied tank and in the tank without ozone treatment. The microbiological contamination during storage did not exceed the allowed level; however it was lower in the ozone treated wheat grain than in the ozone untreated grain. The ozone treatment did not affect the grain quality parameters. The grain germination rate for 3 and 5 days of the ozone treated grain was about 20% higher than that of the untreated grain. During storage, microbiological contamination did not exceed the permissible level, but ozone treated grains were lower than those of untreated, grain quality indicators were not affected by ozone treatment, germination of ozone treated grains was about 20% higher than untreated, baking properties were not affected by ozone treatment. The treatment of grain with ozone makes stored grain more expensive approximately 5.00 EUR per ton, due to additional technical equipment required to ensure the ozone treatment process. One can conclude from the attained results that processing the restored grain under the conditions mentioned reduces the grain microbiological contamination; it does not affect the grain quality parameters and baking properties; it slightly improves the grain germination rate and has no impact upon the shell of the grain. © 2021 Adolfs Rucins, Evita Straumite, Dainis Viesturs, Alberts Kristins.
- ItemEnergy level determination of purine containing blue light emitting organic compounds(SPIE - International Society for Optics and Photonics, 2018) Grzibovskis, Raitis; Vembris, Aivars; Sebris, Armands; Kapilinskis, Zigfrids; Turks, MarisOrganic light emitting diodes (OLED) have found their applications in the mobile and TV screens. Till now the commercially available diodes are made by expensive thermal evaporation in a vacuum. The costs of OLED fabrication could be decreased by applying low-cost wet casting methods, for example, spin-coating. In this work, we have studied a group of blue light emitting purine derivatives which could potentially be used in OLEDs. The advantage of these compounds is their ability to form amorphous thin films from solutions. All the thin films were prepared by the spincoating method from chloroform solution on ITO glass. The position of hole and electron transport energy levels is important for efficient OLED fabrication. Ionization energy was determined using photoelectron yield spectroscopy. The gap between ionization energy and electron affinity was determined using photoconductivity measurements. Electron affinity (Ea) then was calculated as a difference between ionization energy (I) and photoconductivity threshold value (Eth). Changes in the energy level values depending on the molecule structure were investigated. The position of electron acceptor group strongly affects the gap between ionization energy and electron affinity, while with the help of the attached substitute groups it is possible to alter the ionization energy. Fine “tuning” of the ionization energy values can be achieved by altering the length of the “tail” where the inactive bulky group is attached.
- ItemCharacterization of crystalline structure and morphology of Ga2O3 thin film grown by MOCVD technique(Trans Tech Publications Ltd., 2017) Kjapsna, Alvars; Dimitrocenko, Lauris; Tale, Ivars; Trukhin, Anatoly; Ignatans, Reinis; Grants, RolandsGrowth of gallium oxide thin film was realized with MOCVD on (0001) sapphire substrate. Structural and compositional properties of thin film were studied employing trimethylgallium and water as precursors, carrier gases were H2 and N2. Obtained film is polycrystalline and predominantly consisted of (201) oriented β-Ga2O3. Sample exhibited blue luminescence which is attributed to oxygen vacancies. H2 gas proved to have beneficial effect on film quality and overall growth process.
- ItemSynthesis of Eu2+ and Dy3+ doped strontium aluminates and their properties(Trans Tech Publications Ltd., 2017) Rozenberga-Voska, Laura; Grabis, Janis; Zolotarjovs, AleksejsStrontium aluminate phosphors were synthesized by the solution combustion method using citric acid, urea or glycine as reducing agent and europium and dysprosium as dopants. The content of both dopants was in the range of 1-2 mol%. Dependence of phase composition, crystallite size and specific surface area on calcinations temperature, used reducing agents and dopants were determined. Luminescent properties of the calcinated at 1300 °C powders contained SrAl2O4 (90 %) and Sr4Al24O25 (10%) phases with crystallite size of 80 nm were determined.