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241 results on '"Smits, Krisjanis"'

5. Ultraviolet luminescence of polycyclic aromatic hydrocarbons in partially consolidated sol-gel silica glasses

Author

Skuja, Linards, Leimane, Madara, Bite, Ivita, Millers, Donats, Zolotarjovs, Aleksejs, Vitola, Virginija, and Smits, Krisjanis

Subjects
Condensed Matter - Materials Science
Abstract

Photoluminescence (PL) and Raman spectra of sol-gel-derived silica glasses were studied in course of the consolidation of xerogel to dense glass. A number of ultraviolet PL bands in 3 eV - 4 eV region were found, which have not been observed in pure silica glasses not exposed to carbon compounds. Such PL bands, some of which exhibit distinct vibronic structures at room temperature, have been persistently reported in various high-surface porous or nanoparticle forms of SiO2. Based on their spectral shapes and decay kinetics properties, the structured PL bands in the 3.7-3.8 eV and 3.1-3.3 eV regions are assigned to polycyclic hydrocarbons, naphthalene and pyrene, respectively, which are formed from ethanol molecules created by hydrolysis of tetraethoxysilane. These data support the hypothesis that PL activity of carbon-doped silica may be related to embedded aromatic carbon groups., Comment: 19 pages, including 11 figures. Pre-final manuscript of a paper, submitted end of August 2021

Published
2021
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8. Optical absorption of excimer laser-induced dichlorine monoxide in silica glass and excitation of singlet oxygen luminescence by energy transfer from chlorine molecules

Author

Skuja, Linards, Ollier, Nadège, Kajihara, Koichi, Bite, Ivita, Leimane, Madara, Smits, Krisjanis, and Silins, Andrejs

Subjects
Condensed Matter - Materials Science
Abstract

An optical absorption (OA) band of interstitial dichlorine monoxide molecules with peak at 4.7 eV and halfwidth 0.94 eV is identified in F2 laser - irradiated (photon energy=7.9 eV) synthetic silica glass bearing both interstitial O2 and Cl2 molecules. Alongside with intrinsic defects, this OA band can contribute to solarization of silica glasses produced from SiCl4. While the formation of ClClO is confirmed by its Raman signature, its structural isomer ClOCl may also contribute to this induced OA band. Thermal destruction of this band between 300C and 400C almost completely restores the pre-irradiation concentration of interstitial Cl2. An additional weak OA band at 3.5 eV is tentatively assigned to ClO2 molecules. The strongly forbidden 1272nm infrared luminescence band of excited singlet O2 molecules was observed at 3 eV-3.5 eV excitation, demonstrating an energy transfer process from photoexcited triplet Cl2 to O2. The energy transfer most likely occurs between Cl2 and O2 interstitial molecules located in neighboring nanosized interstitial voids in the structure of SiO2 glass network., Comment: 25 manuscript pages, 9 figures, published 2021

Published
2021
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18. Sustainable and fast synthesis of zinc-phthalocyanine for gamma radiation dosimeter application

Author

Vasiljević, Bojana, Odobaša, Daliborka, Vujičić, Ivica, Budimir Filimonović, Milica, Smits, Krisjanis, Mijin, Dušan, Marinković, Dragana, Vasiljević, Bojana, Odobaša, Daliborka, Vujičić, Ivica, Budimir Filimonović, Milica, Smits, Krisjanis, Mijin, Dušan, and Marinković, Dragana

Abstract

In the present research, the two different systems of dye based on zinc phthalocyanine were prepared by microwave-induced synthesis and conventional methods. They were evaluated as new effective chemical-based dosimeters for gamma irradiation. The sensitivity of the prepared dosimeters was examined by studying the comparative results between them through the changes in structural and optical properties upon exposure to different gamma irradiation doses. The color bleaching of the solutions was followed spectrophotometrically. Gradual changes from blue to light yellow color of zinc phthalocyanine solution, with the increase of the gamma radiation dose, were observed due to the decomposition of the dyes based on the zinc phthalocyanine. The synthesized zinc phthalocyanine chemical-based dosimeters for measurement of gamma irradiation up to 25kGy showed excellent stability after irradiation in terms of morphology and structure, which makes them a suitable novel material as composite-based dosimeters of gamma irradiation.

Published
2024

30. Impact of Europium and Niobium Doping on Hafnium Oxide (HfO 2): Comparative Analysis of Sol–Gel and Combustion Synthesis Methods.

Author

Laganovska, Katrina, Vitola, Virginija, Einbergs, Ernests, Bite, Ivita, Zolotarjovs, Aleksejs, Leimane, Madara, Tunens, Gatis, and Smits, Krisjanis

Subjects
HAFNIUM oxide, EUROPIUM, NIOBIUM, COMPARATIVE studies, SELF-propagating high-temperature synthesis, SOL-gel processes
Abstract

This study compares HfO2 ceramics synthesized using sol–gel and combustion methods, emphasizing the impact of the method of synthesis on the resulting properties of the material. The research findings illustrate morphological differences between sol–gel and combustion-derived HfO2. While sol–gel samples displayed irregular nanoparticles with pronounced boundaries, combustion samples revealed more homogeneous structures with particles tending towards coalescence. It was discerned that Eu3+ doping induced oxygen vacancies, stabilizing the tetragonal phase, while subsequent doping with Nb5+ significantly reduced these vacancies, which was also observed in photoluminescence analysis. Furthermore, combustion synthesis left fewer organic residues, with urea presence during synthesis contributing to residual organic components in the material. XPS analysis was used to evaluate the presence of oxygen-deficient hafnia sub-oxide in the samples. The study underscores the important role of tailored synthesis methods in optimizing the properties and applications of HfO2. [ABSTRACT FROM AUTHOR]

Published
2024
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41. Hydrothermal Synthesis and Properties of Yb3+/Tm3+ Doped Sr2LaF7 Upconversion Nanoparticles

Author

Milićević, Bojana R., Periša, Jovana, Ristić, Zoran, Milenković, Katarina, Antić, Željka, Smits, Krisjanis, Kemere, Meldra, Vitols, Kaspars, Sarakovskis, Anatolijs, Dramićanin, Miroslav, Milićević, Bojana R., Periša, Jovana, Ristić, Zoran, Milenković, Katarina, Antić, Željka, Smits, Krisjanis, Kemere, Meldra, Vitols, Kaspars, Sarakovskis, Anatolijs, and Dramićanin, Miroslav

Abstract

We report the procedure for hydrothermal synthesis of ultrasmall Yb3+/Tm3+ co-doped Sr2LaF7 (SLF) upconversion phosphors. These phosphors were synthesized by varying the concentrations of Yb3+ (x = 10, 15, 20, and 25 mol%) and Tm3+ (y = 0.75, 1, 2, and 3 mol%) with the aim to analyze their emissions in the near IR spectral range. According to the detailed structural analysis, Yb3+ and Tm3+ occupy the La3+ sites in the SLF host. The addition of Yb3+/Tm3+ ions has a huge impact on the lattice constant, particle size, and PL emission properties of the synthesized SLF nanophosphor. The results show that the optimal dopant concentrations for upconversion luminescence of Yb3+/Tm3+ co-doped SLF are 20 mol% Yb3+ and 1 mol% Tm3+ with EDTA as the chelating agent. Under 980 nm light excitation, a strong upconversion emission of Tm3+ ions around 800 nm was achieved. In addition, the experimental photoluminescence lifetime of Tm3+ emission in the SLF host is reported. This study discovered that efficient near IR emission from ultrasmall Yb3+/Tm3+ co-doped SLF phosphors may have potential applications in the fields of fluorescent labels in bioimaging and security applications.

Published
2023

44. Tungsten–SiO 2 –Based Planar Field Emission Microtriodes with Different Electrode Topologies.

Author

Avotina, Liga, Bikse, Liga, Dekhtyar, Yuri, Goldmane, Annija Elizabete, Kizane, Gunta, Muhin, Aleksei, Romanova, Marina, Smits, Krisjanis, Sorokins, Hermanis, Vilken, Aleksandr, and Zaslavskis, Aleksandrs

Subjects
FIELD emission, FOCUSED ion beams, X-ray photoelectron spectroscopy, ATOMIC force microscopy, ELECTRIC fields, ELECTRODES
Abstract

This study examines the electrical properties and layer quality of field emission microtriodes that have planar electrode geometry and are based on tungsten (W) and silicon dioxide (SiO2). Two types of microtriodes were analyzed: one with a multi-tip cathode fabricated using photolithography (PL) and the other with a single-tip cathode fabricated using a focused ion beam (FIB). Atomic force microscopy (AFM) analysis revealed surface roughness of the W layer in the order of several nanometers (Ra = 3.8 ± 0.5 nm). The work function values of the Si substrate, SiO2 layer, and W layer were estimated using low-energy ultraviolet photoelectron emission (PE) spectroscopy and were 4.71 eV, 4.85 eV, and 4.67 eV, respectively. The homogeneity of the W layer and the absence of oxygen and silicon impurities were confirmed via X-ray photoelectron spectroscopy (XPS). The PL microtriode and the FIB microtriode exhibited turn-on voltages of 110 V and 50 V, respectively, both demonstrating a field emission current of 0.4 nA. The FIB microtriode showed significantly improved field emission efficiency compared to the PL microtriode, attributed to a higher local electric field near the cathode. [ABSTRACT FROM AUTHOR]

Published
2023
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