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Matze meets... Podcast
(2023)
Die Welt kleiner Partikel
(2023)
Solid State Synthesis and Reflection Spectra of Ce2Zr3(MoO4)9:Ti and Ce2Zr3(MoO4)9:Ti,Eu, FEMS
(2023)
Semiconductors
(2022)
UV emitting nanoparticles enhance the effect of ionizing radiation in 3D lung cancer spheroids
(2022)
Crystallographic and Photoluminescence Studies on the Solid Solution Li3Ba2La3–xPrx(WO4)8 (x = 0-3
(2022)
Spectroscopic Studies on Pr3+ Doped LuPO4 and YPO4 upon VUV and Synchrotron Radiation Excitation
(2022)
Eloxal and Particle Coatings
(2022)
Up-Converters
(2022)
Scintillators
(2022)
Inorganic Detetor Materials
(2022)
This work deals with the spectroscopic properties of praseodymium doped single crystalline lutetium aluminum garnet (LuAG:Pr3+). A special focus was set on temperature- and time-dependent spectroscopy. Beyond the well-known down-conversion luminescence of LuAG:Pr3+, also UV-A/B up-conversion luminescence under excitation with a 488 nm laser was thoroughly investigated. Furthermore, the results of the spectroscopic investigations on the single crystalline material were supplemented and compared with measurements on a microscale powder sample.
In addition, to the spectroscopic investigations, mechanistic considerations are presented to obtain a closer look at the up-conversion process in LuAG:Pr3+. We promote the thesis of a temperature-dependent energy transfer up-conversion mechanism.
We report on a watt-level highly efficient europium laser operating at the 5D0→7F4 transition. It is based on the stoichiometric KEu(WO4)2 crystal. Under pumping by a green laser at 532.1 nm, the KEu(WO4)2 laser generated a maximum peak output power of 1.11 W at ∼703nm with a slope efficiency of 43.2% and a linear polarization (????‖????????). A laser threshold as low as 64 mW was achieved. True continuous-wave operation was demonstrated. The polarized emission properties of monoclinic KEu(WO4)2 were determined.
The quaternary tungstates Li3Ba2RE3(WO4)8 (RE = La-Nd, Sm-Ho) were obtained by a ceramic synthesis route and were characterized by powder and single crystal X-ray diffraction. The structures of Li3Ba2Pr3(WO4)8 and Li3Ba2Tb3(WO4)8 were refined from single crystal diffractometer data: RbLiBi2(MoO4)4 type, space group C2/c, a = 528.57(2), b = 1292.39(6), c = 1934.80(10) pm, b = 91.522(4)°, 2151 F2 values, 108 parameters for Li3Ba2Pr3(WO4)8 and a = 520.54(2), b = 1272.03(6), c = 1918.85(10) pm, b = 91.948(4)°, 2020 F2 values, 108 variables for Li3Ba2Tb3(WO4)8. Striking polyhedral building units in these tungstates are WO4 tetrahedra and LiO6 octahedra, while the mixed occupied site and the barium atoms have higher coordination numbers, i.e. RE/Li@O8 and Ba@O10. In addition to the powder quality assessment by means of reflection spectroscopy, the synthesized samples were studied for their suitability as a scintillator material. Therefore, X-ray excited luminescence measurements where performed. Apart from Li3Ba2Ce3(WO4)8 and Li3Ba2Nd3(WO4)8, all compounds show strong emission under X-ray irradiation. Li3Ba2La3(WO4)8 and Li3Ba2Gd3(WO4)8 show blue CT luminescence caused by tungstate units, while the other samples show typical and multiple lines due to well known [Xe]4fn → [Xe]4fn transitions.
Phenanthroline chromophore as efficient antenna for Tb3+ green luminescence: A theoretical study
(2021)
On the Opportunities of the Use of Luminescence Standards for Cuvette Spectrometer, WODIL 2021
(2021)
Kinetic Monte Carlo Simulations for Solid State Ionics: Case Studies with the MOCASSIN Program, Diff
(2021)
The Effect of Ionic Defect Interactions on the Hydration of Yttrium-Doped Barium Zirconate, Phys
(2021)
The use of hydraulic fracturing (HF) to extract oil and natural gas has increased, along with intensive discussions on the associated risks to human health. Three technical processes should be differentiated when evaluating human health risks, namely (1) drilling of the borehole, (2) hydraulic stimulation, and (3) gas or oil production. During the drilling phase, emissions such as NOx, NMVOCs (non-methane volatile organic compounds) as precursors for tropospheric ozone formation, and SOx have been shown to be higher compared to the subsequent phases. In relation to hydraulic stimulation, the toxicity of frac fluids is of relevance. More than 1100 compounds have been identified as components. A trend is to use fewer, less hazardous and more biodegradable substances; however, the use of hydrocarbons, such as kerosene and diesel, is still allowed
in the USA. Methane in drinking water is of low toxicological relevance but may indicate inadequate integrity of the gas well.
There is a great concern regarding the contamination of ground- and surface water during the production phase. Water that flows to the surface from oil and gas wells, so-called ‘produced water’, represents a mixture of flow-back, the injected frac fluid returning to the surface, and the reservoir water present in natural oil and gas deposits. Among numerous hazardous compounds, produced water may contain bromide, arsenic, strontium, mercury, barium, radioactive isotopes and organic compounds, particularly benzene, toluene, ethylbenzene and xylenes (BTEX). The sewage outflow, even from specialized treatment plants, may still contain critical concentrations of barium, strontium and arsenic. Evidence suggests that the quality of groundwater and surface water may be compromised by disposal of produced water. Particularly critical is the use of produced water for watering of agricultural areas, where persistent compounds may accumulate. Air contamination can occur as a result of several HF-associated activities. In addition to BTEX, 20 HF-associated air contaminants are group 1A or 1B carcinogens according to the IARC. In the U.S., oil and gas production (including conventional production) represents the second largest source of anthropogenic methane emissions. High-quality epidemiological studies are required, especially in light of recent observations of an association between childhood leukemia and multiple myeloma in the neighborhood of oil and gas production sites. In conclusion, (1) strong evidence supports the conclusion that frac fluids can lead to local environmental contamination; (2) while changes in the chemical composition of soil, water and air are likely to occur, the increased levels are still often below threshold values for safety; (3) point source pollution due to poor maintenance of wells and pipelines can be monitored and remedied; (4) risk assessment should be based on both hazard and exposure evaluation; (5) while the concentrations of frac fluid chemicals are low, some are known carcinogens; therefore, thorough, well-designed studies are needed to assess the risk to human health with high certainty; (6) HF can represent a health risk via long-lasting contamination of soil and water, when strict safety measures are not rigorously applied.
The global demand on highly purified gases provided by energy-efficient separation processes grows steadily since decades. An example of particular industrial relevance is nitrogen generated by pressure swing adsorption from compressed air. A kinetically based separation of oxygen from nitrogen is possible by means of carbon molecular sieves (CMS) since oxygen adsorbs remarkably faster in CMS than nitrogen. Even high product purities (5–1000 ppm O2) are easily achievable in commercial generators. However, only a few studies present experimental findings in this purity range. That comes as no surprise, since experimental conditions are not standardised and the determination of N2-PSA performance indicators still creates an experimental challenge. Moreover, the design of the set-up remarkably influences the experimental results. Thus it is the motivation of this study to develop a multi-step strategy, comprising the definition of a reference process, the derivation of explicit and implicit performance indicators based on either flow meter readings or macroscopic material balances, a verification strategy for experimentally obtained data, and an error consideration, which advices accuracy requirements for analysers and flow meters. The effect of cycle time and operating temperature on the performance indicators is exemplarily studied at high purities by means of the proposed strategy.
Modelling and Experimental Investigation of Luminous Coupling in UVLED Driven Optical Fiber Reactors
(2020)
Lead (Pb) exposure of consumers and the environment has been reduced over the past decades. Despite all measures taken,
immission of Pb onto agricultural soils still occurs, with fertilizer application, lead shot from hunting activities, and Pb
from air deposition representing major sources. Little is known about the intermediate and long-term consequences of these
emissions. To gain more insight, we established a mathematical model that considers input from fertilizer, ammunition,
deposition from air, uptake of Pb by crops, and wash-out to simulate the resulting Pb concentrations in soil over extended
periods. In a further step, human oral exposure by crop-based food was simulated and blood concentrations were derived
to estimate the margin of exposure to Pb-induced toxic effects. Simulating current farming scenarios, a new equilibrium
concentration of Pb in soil would be established after several centuries. Developmental neurotoxicity represents the most
critical toxicological effect of Pb for humans. According to our model, a Pb concentration of ~ 5 mg/kg in agricultural soil
leads to an intake of approximately 10 μg Pb per person per day by the consumption of agricultural products, the dose corresponding
to the tolerable daily intake (TDI). Therefore, 5 mg Pb/kg represents a critical concentration in soil that should
not be exceeded. Starting with a soil concentration of 0.1 mg/kg, the current control level for crop fields, our simulation
predicts periods of ~ 50 and ~ 175 years for two Pb immission scenarios for mass of Pb per area and year [scenario 1: ~ 400 g
Pb/(ha × a); scenario 2: ~ 175 g Pb/(ha × a)], until the critical concentration of ~ 5 mg/kg Pb in soil would be reached. The
two scenarios, which differ in their Pb input via fertilizer, represent relatively high but not unrealistic Pb immissions. From
these scenarios, we calculated that the annual deposition of Pb onto soil should remain below ~ 100 g/(ha × a) in order not to
exceed the critical soil level of 5 mg/kg. We propose as efficient measures to reduce Pb input into agricultural soil to lower
the Pb content of compost and to use alternatives to Pb ammunition for hunting.
Hazardous substances
(2020)
This title presents a detailed overview on the full range of hazard categories and the associated risks of chemicals. It provides a basic introduction into toxicology, ecotoxicology and environmental behavior and enables all who perform precise chemical analysis to handle substances according to their intrinsic properties such as physical-chemical, environmental, ecological and toxicological hazards.