Evolution of free volumes in polycrystalline baga2o4 ceramics doped with eu3+ ions

H.K. and Y.K. would like to thank A. Ingram for assistance in PAL experiments. The authors thank E.A. Kotomin and M. Brik for the many useful discussions. The research was (partly) performed in the Institute of Solid State Physics, University of Latvia ISSP UL. ISSP UL as the Center of Excellence is supported through the Framework Program for European universities Union Horizon 2020, H2020-WIDESPREAD-01–2016–2017-TeamingPhase2 under Grant Agreement No. 739508, CAMART2 project.BaGa2O4 ceramics doped with Eu3+ ions (1, 3 and 4 mol.%) were obtained by solid-phase sintering. The phase composition and microstructural features of ceramics were investigated using X-ray diffraction and scanning electron microscopy in comparison with energy-dispersive methods. Here, it is shown that undoped and Eu3+-doped BaGa2O4 ceramics are characterized by a developed structure of grains, grain boundaries and pores. Additional phases are mainly localized near grain boundaries creating additional defects. The evolution of defect-related extended free volumes in BaGa2O4 ceramics due to the increase in the content of Eu3+ ions was studied using the positron annihilation lifetime spectroscopy technique. It is established that the increase in the number of Eu3+ ions in the basic BaGa2O4 matrix leads to the agglomeration of free-volume defects with their subsequent fragmentation. The presence of Eu3+ ions results in the expansion of nanosized pores and an increase in their number with their future fragmentation. © 2021 by the authors. Licensee MDPI, Basel, Switzerland. Published under the CC BY 4.0 license.This work was supported by the Ministry of Education and Science of Ukraine (project for young researchers No. 0119U100435) for H.K and Y.K.; the National Research Foundation of Ukraine (project 2020.02/0217) for I.K. and H.K. as well as by the Latvian research council via the Latvian National Research Program under the topic “High-Energy Physics and Accelerator Technologies”, Agreement No: VPP-IZM-CERN-2020/1-0002, for V.P. and A.I.P; ISSP UL as the Center of Excellence is supported through the Framework Program for European universities Union Horizon 2020, H2020-WIDESPREAD-01–2016–2017-TeamingPhase2 under Grant Agreement No. 739508, CAMART2 project

Luminescence Properties and Decay Kinetics of Mn 2+ and Eu 3+ Co-Dopant Ions in MgGa 2 O 4 Ceramics

A. Luchechko gratefully acknowledges a grant from the Institute of Physics PAS for a research visit to the institute, while A.I. Popov has been supported by project LZP-2018/1-0214 from the Latvian Council of Science.The MgGa 2 O 4 ceramics co-doped with Mn 2+ and Eu 3+ ions were synthesized via a higherature solid-state reaction technique. The samples with various Eu 3+ concentrations were characterised using high-resolution photoluminescence (PL) spectroscopy. The PL spectra show weak matrix emission in a blue spectral region with dominant excitation band around 380 nm. Manganese ions are highly excited deeply in UV region and exhibit emission band peaked at 502 nm. The Eu 3+ ions show characteristic f-f excitation and emission lines. The energy transfer between host defects and activator ions was observed. Luminescence decay curves of Mn 2+ and Eu 3+ emission showed complex kinetics with both Eu 3+ -ion concentration and excitation wavelength changes.Latvian Council of Science LZP-2018/1-0214; Latvian–Ukrainian Joint Research Project LV-UA/2016/1,M/.8-2018; project DB/RIDER0117U004443; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Chemical tuning of photo- and persistent luminescence of Cr3+-activated beta-Ga2O3 by alloying with Al2O3 and In2O3

An effect of alloying of the monoclinic beta- Ga2O3 with Al2O3 and In2O3 on the photoluminescent, thermoluminescent and persistent luminescent properties of Cr3+ ions has been comprehensively investigated. For this purpose, various series of Cr3+ and Ca2+ co-doped microcrystalline phosphors were synthesized by the solution combustion method, including pseudobinary compounds like (Ga-Al)2O3 with up to 20% Al and (Ga-In)2O3 with up to 50% In as well as pseudoternary compounds (Ga Al In)2O3 with balanced proportion of Al, Ga and In. The phase composition and crystal structure of the obtained materials were examined by X-ray powder diffraction technique. Detailed luminescence studies were conducted for the (Ga-Al)2O3 and (Ga-In)2O3 compounds which exhibited a single-phase monoclinic structure. Low-temperature and time-resolved photoluminescence investigations of the Cr-doped pseudobinary compounds unveiled several types of Cr3+ centres, attributed to the Al-, Ga- and In-centred octahedra in the studied alloys. The obtained results underscore the benefit of bandgap engineering through alteration in the host lattice chemical composition for efficient tuning of the thermoluminescent and persistent luminescent properties of the near-infrared-emitting beta Ga2O3:Cr based phosphors. Furthermore, it was demonstrated that modification of the chemical composition of the host lattice also adjusts the thermometric performance of the studied phosphors. Indeed, the specific sensitivity of the beta- Ga2O3:Cr3+ decay time luminescence thermometer showed nearly twofold enhancement when the host lattice was alloyed with 30% of In2O3.Comment: 35 pages, 14 figure

Afterglow, TL and OSL properties of Mn2+-doped ZnGa2O4 phosphor

The work was supported by Latvian Research Council via LZP-2018/1–0214 research project as well as the Latvian-Ukrainian Joint Research Project (LV-UA/2016/1 in Latvia and M/8-2018 (No. 0118U001672) in Ukraine), and by the NATO SfP Project G4649. The work was also partially supported by the Polish National Science Center (project 2018/31/B/ST8/00774). A. Luchechko gratefully acknowledges a grant from Institute of Physics PAS for a research visit to the Institute.Zinc gallate (ZnGa2O4) spinel ceramics doped with Mn2+ ions was prepared by a solid-state reaction at 1200 °C in air. Manganese concentration was equal to 0.05 mol.% of MnO with respect to ZnO. Ceramics produced in this way show an efficient green emission at about 505 nm under UV or X-ray excitations, which is caused by Mn2+ ions. This green emission is observed also as a relatively long afterglow (visible to the naked eye in the dark for about one hour) after switching-off the X-ray excitation. Time profiles of the beginning of glow and afterglow have been studied together with thermally stimulated (TSL) and optically stimulated (OSL) luminescence. Experimental results demonstrate a presence of few types of shallow and deep traps responsible for the observed afterglow and TSL/OSL emission of the material. The possibility of pulsed optical stimulation and time-resolved OSL characteristics of ZnGa2 O4: Mn2+ has been reported for the first time. The presented results suggest the ZnGa2O4: Mn2+ spinel as a promising material for further fundamental research and possibility of application as a green long-lasting phosphor or storage phosphor for TSL/OSL radiation dosimetry.North Atlantic Treaty Organization G4649; Polish National Science Center project 2018/31/B/ST8/00774; 0118U001672,LV-UA/2016/1,LZP-2018/1–0214; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Atributivne lastnosti lune v ukrajinskih in angleških ljudskih ugankah

V prispevku so z metodo kontrastivne analize raziskane posebnosti konceptualizacije lune v ukrajinskih in angleških ugankah. Raziskava temelji na besedilih iz najbolj popolnih zbirk ukrajinskih ugank – Uganke (1962), ki jih je uredil I. Berezovsky, in angleških ugank English Riddles from Oral Tradition (1951), ki jih je uredil A. Taylor. V prispevku so ugotovljene skupne značilnosti in razlike v motivacijski osnovi kodifikatorjev lune, ob tem pa so navedene njene asociativne vzporednice, ki se verbalizirajo v primerjanih ljudskih ugankah. Predstave o luni, ki jih je kolektivna zavest govorcev ukrajinskega in angleškega jezika osmislila na novo, so rekonstruirane na podlagi njenih najbolj univerzalnih atributivnih lastnosti, ki so eksplicitno oz. implicitno predstavljene v besedilih ljudskih ugank. The paper attempts to provide a contrastive study of the riddle manifestation of the Ukrainian and English conception of the Moon. The article examines the corpus of Ukrainian and English riddles for the Moon found mainly in major Ukrainian and English riddle collections – Riddles (1962) edited by I. Berezovskyi and English Riddles from Oral Tradition (1951) edited by A. Taylor. It focuses on tracing the common and national features of Moon codifiers (associative parallels) as well as their motivation verbalised in riddle corpora under comparison. The Ukrainian and English conception of the Moon is reconstructed through its similar attributive features of the encoded object and its codifiers explicitly and/or implicitly represented in riddles from oral tradition

Термостимульована люмінесценція і провідність кристалів β-Ga2O3

Розглянуто термостимульовану люмінесценцію (ТСЛ) та термостимульовану провідність (ТСП) нелегованих монокристалів β-Ga2O3. Досліджувані зразки являли собою монокристали β-Ga2O3, вирощені методом оптичної зони плавки, які потім піддавали відпалу в атмосфері кисню або аргону. Отримані спектри фотолюмінесценції є типовими для монокристалів β-Ga2O3: вони містять широку смугу випромінювання матриці при 320-550 нм, а також слабку люмінесценцію з максимумом при 700 нм приписану ненавмисно введеній домішці Cr3+. Після опромінення Х-променями зразки демонструють інтенсивну ТСЛ в діапазоні температур 85-500 K. На кривих ТСЛ і ТСП цих кристалів наявні три низькотемпературні піки при 116, 147 і 165 K. Глибини пасток, що відповідають за ці піки, становлять 0.15, 0.2 і 0.3 еВ, відповідно. Високотемпературні піки ТСЛ при 354, 385 і 430 K з відповідними енергіями активації 0.84, 1.0 і 1.1 еВ спостерігаються в зразках, відпалених в атмосферах кисню або аргону. Криві TСП добре узгоджуються з результатами дослідження ТСЛ. Встановлена кореляція між відпалом кристалів в окислювальній та інертній атмосферах і власними дефектами в монокристалах β-Ga2O3.The paper deals with thermostimulated luminescence (TSL) and thermostimulated conductivity (TSC) of unintentionally doped (UID) β-Ga2O3 single crystals. The samples under study were β-Ga2O3 single crystals grown by the floating zone method with radiation heating and then subjected to annealing in an atmosphere of oxygen or argon. The obtained photoluminescence emission spectra are typical for β-Ga2O3 single crystals: they contain the broad emission band of the host at 320-550 nm as well as a weak luminescence with maximum at 700 nm due to the unintentional Cr3+ impurities. After exposure to X-ray radiation, the samples exhibit intense TSL at the temperature range of 85-500 K. Three low-temperature peaks at 116, 147 and 165 K are present in TSL and TSC curves of these crystals. The depths of the traps responsible for these peaks are 0.15, 0.2 and 0.3 eV, respectively. The high-temperature TSL peaks at 354 K, 385 K and 430 K with corresponding activation energies of 0.84, 1.0 and 1.1 eV were observed in samples annealed in argon or oxygen atmospheres. The TSС curves are in good agreement with the results of the TSL study. A correlation between annealing of crystals in oxidizing and inert atmospheres and intrinsic defects in single crystals β-Ga2O3 has been established

X-ray excited luminescence of ytterbium containing YAG single crystalline films

Luminescence properties of ytterbium ions in of У₃AI₅О₁₂ (УAG) epitaxial films have been investigated. The influence of growth conditions on the change of activator ions charge state and the luminescence in visible spectral region has been demonstrated. It has been established that emission bands with maxima at 480 and 580 nm are attributed to the 5d-4f transitions of Уb²⁺ ions. The emission bands with maxima at 330 nm and 500 nm correspond to transitions from charge transfer state to ²F₇/₂ and and ²F₅/₂ state of Уb³⁺ ions, respectively.Проведено исследование люминесцентных свойств ионов иттербия в эпитаксиальных пленках У₃AI₅О₁₂ (УAG). Показано влияние условий выращивания на изменение зарядового состояния ионов активатора и его свечения в видимой области спектра. Установлено, что люминесценция в полосах с максимумами при 480 нм и 580 нм в эпитаксиальных пленках УAG:Уb приписывается 5d-4f переходам ионов Уb²⁺. Полосы свечения с максимумами при 330 и 500 нм отвечают переходам из состояния переноса заряда соответственно на уровни ²F₇/₂ и ²F₅/₂ ионов Уb³⁺.Проведено дослiдження люмiнесцентних властивостей iонiв iтербiю в епiтаксiйних плiвках У₃AI₅О₁₂ (УAG). Показано вплив умов вирощування на змiну зарядового стану iонiв активатора та його свiчення у видимiй областi спектра. Встановлено, що люмiнеcценцiя в смугах з максимумами при 480 нм i 580 нм приписується 5d-4f переходам iонiв Уb²⁺. Смуги свiчення з максимумами при 330 i 500 нм вiдповiдають переходам зi стану перенесення заряду вiдповiдно на рiвнi ²F₇/₂ i ²F₅/₂ iонiв Уb³⁺