Luminescence-site symmetry correlations in Dy3+ doped alkali-alkaline earth orthoborates of the type XZBO3 with X = Li, Na, K and Z = Mg, Ca, Ba. - In: Journal of luminescence. - New York, NY [u.a.] : Elsevier, ISSN 0022-2313, Bd. 241 (2022), 118429
- Im Titel ist "3+" hochgestellt und "3" tiefgestellt
A systematic investigation of the luminescence properties of Dy3+ doped alkali-alkaline earth orthoborates of the stoichiometric composition XZBO3 with X = Li, Na, K and Z = Mg, Ca, Ba was conducted. XRD diffractograms show that the compounds LiMgBO3, LiCaBO3, LiBaBO3, NaMgBO3, NaCaBO3, NaBaBO3, and KMgBO3 could be produced in high purity. Relatively intense luminescence was observed only for the phases LiCaBO3, NaMgBO3, NaCaBO3 and NaBaBO3. Micro Raman investigations show that the Dy3+ luminesence mainly originates from the orthoborate phase in these samples. Photo-luminescence spectroscopy of LiCaBO3, NaCaBO3 and NaBaBO3 shows the typical Dy3+ emission with the prominent emission peak in the yellow spectral range around 575 nm. A second, but much less intense peak is observed at around 485 nm (cyan). The luminescence emission spectrum of Dy3+:NaMgBO3 is much different: here, the highest emission intensity is observed at about 485 nm. It is proposed that the Dy3+ ions occupy the Na positions in this crystal phase which has a much higher symmetry than the alkaline earth positions in the other examined crystal phases. This is supported by broadened and more split up peaks in the excitation and emission spectra of Dy3+:NaMgBO3 suggesting a much stronger local crystal field at the rare earth position in this compound. The results are additionally compared to spectroscopic data of different well known Dy3+ doped crystalline compounds and Dy3+ and Eu3+ doped alkali-alkaline earth orthoborates from other publications, which offer further insight into the relation between the crystallographic sites of the doped rare earth ions and their luminescence.
Yttrium and rare-earth modified lithium orthoborates: glass formation and vibrational activity. - In: Journal of non-crystalline solids. - Amsterdam [u.a.] : Elsevier Science, ISSN 0022-3093, (2021), 121152
Glass formation and structure-property relations were explored in highly modified borate glasses containing high loads of rare-earth elements, whose crystalline analogues display a trigonal to tetrahedral borate phase transition (BO33- -> BØ2O23-, where Ø and O- indicate bridging and non-bridging oxygen atoms). The resulting borate networks are completely depolymerized, where borate anions are crosslinked to rare-earth and modifier cations via ionic bonds. The borate structure was found to be based on a single structural unit, BO33- triangles, whose fundamental vibrations are all active in both the Raman and infrared. The local environment of the rare-earth ions in orthoborate glasses was studied with far infrared spectroscopy and, in some cases, by using terbium as a probe ion. A linear correlation was obtained between the effective force constant in the far infrared and the field strength of the rare-earth cation.
Implementierung eines Moduls zur großflächigen In-Line Blitzlampentemperung von gesputterten ITO-Schichten. - Ilmenau : Universitätsverlag Ilmenau, 2021. - 1 Online-Ressource (x, 109 Seiten). - (Werkstofftechnik aktuell ; Band 22)
Technische Universität Ilmenau, Dissertation 2020
Die Blitzlampentemperung (Flash Lamp Annealing - FLA) zählt zu den Kurzzeittemperverfahren (Rapid Thermal Annealing - RTA), da die Erwärmung und Abkühlung der Schicht im Bereich von Millisekunden liegen. Die mit Hilfe von Blitzlampen durchgeführte Temperung dient zur oberflächennahen Erwärmung von Festkörpern. Hierbei handelt es sich um einen thermischen Prozess, der Materialeigenschaften verändern kann. Durch die Blitzlampentemperung kann der Schichtwiderstand von transparenten leitfähigen Oxidschichten (Transparent Conductive Oxides - TCO) reduziert und die Transmission im sichtbaren Wellenlängenbereich erhöht werden. In der vorliegenden Forschungsarbeit wird das Prozessverhalten von dynamischen FLA-Prozessen bei Indium-Zinn-Oxid (ITO) Schichten experimentell dargelegt. Dazu wurde der Einfluss von verschiedenen Prozessparametern wie Energiedichte und Pulszeit des Xenonlichtblitzes erforscht. Erste Versuche zur Untersuchung des Einflusses der Blitzwiederholrate und der Geschwindigkeit des Substrates ließen sich erfolgreich durchführen. Die Herstellung aller Schichten erfolgte am Fraunhofer-Institut für Organische Elektronik, Elektronenstrahl- und Plasmatechnik (FEP) in der In-Line Sputteranlage ILA 750. Für die Blitzlampentemperung wurde das Lampensystem Xenon Flash Lamp Modul FLA 2x360w der Firma ROVAK GmbH genutzt. Das Modul ist Bestandteil der Beschichtungsanlage ILA 900 am Fraunhofer FEP und erlaubt sowohl die statische als auch die dynamische FLA-Behandlung von Substraten bis zu einer Größe von 600 mm x 1200 mm. Die unterschiedlichen Einstellungen der Blitze ließen sich optisch vermessen. Für ITO-Schichten mit einer Schichtdicke von 150 nm konnte nach der FLA-Behandlung ein Widerstand von 14 [Ohm] erreicht werden. Für die Transmission im sichtbaren Wellenlängenbereich wurden 87 % erzielt. Diese Werte sind vergleichbar mit einer konventionellen Temperung von ITO-Schichten im Ofen. Erfolgreich ließ sich zeigen, dass der FLAProzess an eine bestehende In-Line Prozessanlage implementiert werden kann.
AES and EDX surface analysis of weathered float glass exposed in different environmental conditions. - In: Journal of non-crystalline solids. - Amsterdam [u.a.] : Elsevier Science, ISSN 0022-3093, Bd. 572 (2021), 121083
To characterize the influence of environmental conditions on glass weathering, two different float glasses were subjected to a six-month outdoor experiment that took place in Durres (seacoast, Albania), Ilmenau (rural, Germany) and Pristina (urban, Kosovo), three sites with largely different environmental conditions. Atmospheric deposits and meteorological conditions led this study to receive information about different weathering behaviour of two types of float glasses. Typical glass degradation effects and reaction products at the glass surface are shown and the impact of weathering and air quality parameters on the formation of reaction products and degradation is discussed. Surface changes have been localized using optical microscopy. Further investigations for receiving chemical information on the contaminations include Auger electron spectroscopy (AES) and scanning electron microscopy (SEM/EDX). Surface analyses indicate a high amount of weathering products such as chlorides, sulphates and carbonates followed by severe delamination effects for both types of glass exposed in Durres and Pristina. In contrast to this, low levels of soiling and degradation for the samples exposed in Ilmenau were detected.
The structure of Gd3+-doped Li2O and K2O containing aluminosilicate glasses from molecular dynamics simulations. - In: Materials. - Basel : MDPI, ISSN 1996-1944, Bd. 14 (2021), 12, S. 1-18
- Im Titel sind "3+" hochgestellt und "2" tiefgestellt
Understanding the atomic structure of glasses is critical for developing new generations of materials with important technical applications. In particular, the local environment of rare-earth ions and their distribution and clustering is of great relevance for applications of rare earth-containing glasses in photonic devices. In this work, the structure of Gd2O3 doped lithium and potassium aluminosilicate glasses is investigated as a function of their network modifier oxide (NMO-Li2O, K2O) to aluminum oxide ratio using molecular dynamics simulations. The applied simulation procedure yields a set of configurations, the so-called inherent structures, of the liquid state slightly above the glass transition temperature. The generation of a large set of inherent structures allows a statistical sampling of the medium-range order of the Gd3+ ions with less computational effort compared to other simulation methods. The resulting medium-range atomic structures of network former and modifier ions are in good agreement with experimental results and simulations of similar glasses. It was found that increasing NMO/Al ratio increases the network modifier coordination number with non-bridging oxygen sites and reduces the overall stability of the network structure. The fraction of non-bridging oxygen sites in the vicinity of Gd3+ ions increases considerably with decreasing field strength and increasing concentration of the network modifier ions. These correlations could be confirmed even if the simulation results of alkaline earth aluminosilicate glasses are added to the analysis. In addition, the structure predictions generally indicate a low driving force for the clustering of Gd3+. Here, network modifier ions of large ionic radii reduce the probability of Gd-O-Gd contacts.
Microstructure investigation and fluorescence properties of europium-doped scheelite crystals in glass-ceramics made under different synthesis conditions. - In: Journal of luminescence. - New York, NY [u.a.] : Elsevier, ISSN 0022-2313, Bd. 238 (2021), 118244
Chemical changes of float glass surfaces induced by different sand particles and mineralogical phases. - In: Journal of non-crystalline solids. - Amsterdam [u.a.] : Elsevier Science, ISSN 0022-3093, Bd. 566 (2021), 120868
Particles play an important role in the storage, transportation and natural weathering of glasses, but their influence on glass degradation is little studied. In this work, the influence of main sand components is investigated. Feldspar exhibits the strongest leaching rate for the network former Na, while quartz has the lowest. The leaching rate of natural sands is in between. Based on these findings, a model describing the leaching mechanism was developed: Hereby, hydroxyl groups adhering on sand grains adsorb network modifiers by substituting their hydrogen by network formers from the glass surface. The amount of available hydroxyl groups determines the leaching rate. This model is supported by loss on ignition performed for the sands, which might be a suitable method to roughly estimate their leaching rates. The adsorption of network modifiers suppresses carbonate formation, dendritic growth and Mg diffusion in the glass surface region. Pimple-like crystal growth is observed.
Sintered porous glasses hosting luminescent species of different nature: Eu3+ ions and Tb3+-doped Ba2TiSi2O8 glass-ceramic powder. - In: Journal of non-crystalline solids. - Amsterdam [u.a.] : Elsevier Science, ISSN 0022-3093, Bd. 531 (2020), 119846
- Im Titel sind "3+" hochgestellt, "2" und "8" tiefgestellt
We report on the employment of a nano-porous Vycor-type glass as host for two luminescent substances of very different physical and chemical nature, which share the same porous space. Firstly, BTS:Tb^3+ glass-ceramic nano-powders were infiltrated in the porous structure and secondly Eu^3+ ions from a nitrate aqueous solution were included afterwards. Upon sintering, the porous silica matrix collapses, embedding both luminescent species. We focused on the micro and nano-structure of the sintered glasses. Upon sintering a europium silicate phase crystallizes as monocrystalline hexagonal nano-rods, which coexist with amorphous round particles below 100 nm enriched in Eu and Si. Both kinds of particles are embedded in a cristobalite matrix. The interesting microstructure is reported for the first time. The sintering heating rate influences the microstructure after the sintering. The microstructure was investigated by a last generation TEM microscope with aberration correction, EDXS and an exhaustive electron diffraction analysis. The inclusion of BTS:Tb^3+ is only limited, and thus, the its role in the optical properties of the final material is negligible. Luminescence upon UV excitation shows the characteristic emission peaks of Eu^3+. This work highlights the possibility of combining several luminescent materials inside a silica matrix.
Crystallization of BaF2 from droplets of phase separated glass - evidence of a core-shell structure by ASAXS. - In: CrystEngComm. - London : RSC, ISSN 1466-8033, Bd. 22 (2020), 30, S. 5031-5039
- Im Titel ist "2" tiefgestellt
Application of hydrosilane-free atmospheric pressure chemical vapor deposition of SiOx films in the manufacture of crystalline silicon solar cells. - In: Thin solid films. - Amsterdam [u.a.] : Elsevier, Bd. 713 (2020), 138338
- Im Titel ist "x" tiefgestellt
In this work we present SiOx films deposited in cost-effective laboratory scale three-dimensional printed atmospheric pressure chemical vapor deposition setup. As SiOx films are deposited at room temperature without complex vacuum systems, they can be a good candidate for the use in commercial c-Si solar cell production lines. The quality of the deposited films was investigated as to their integrity, conformity with various surfaces, and post-treatment resilience such as stability against etchants and annealing. Several applications of the SiOx film prepared with the atmospheric pressure chemical vapor deposition (APCVD) were discussed. In one application, the APCVD SiOx was utilized to effectively promote single-side texturing of Float Zone and Czochralski Si wafers by coating only one side with SiOx and subsequently annealing prior to texturing in an alkaline aqueous solution. Another application was to exploit the APCVD SiOx as a plating mask for silicon heterojunction solar cells. Two processing options prior to the oxide-film deposition were investigated: i) application of an Ag seed-layer, which promotes subsequent electroplating, and ii) printing of an organic grid, which, after stripping, creates openings in the SiOx that facilitate electroplating of the solar cell's electrode on the underlying transparent conducting oxide. In a different application, the APCVD SiOx films acted as protection against parasitic plating on the front side of passivated emitter and rear solar cells. The deposited films were characterized by ellipsometry, hemispherical reflectance measurements, scanning electron microscopy, energy dispersive X-ray spectroscopy and optical microscopy.