Münster University of Applied Sciences

About: Münster University of Applied Sciences is a education organization based out in Münster, Germany. It is known for research contribution in the topics: Luminescence & Laser. The organization has 694 authors who have published 1067 publications receiving 12597 citations.

Photoluminescence and energy transfer behavior of narrow band red light emitting Li3Ba2Tb3(MoO4)8:Eu3+

Abstract: This work concerns the polycrystalline red emitting solid state compound Li3Ba2(Tb1−xEux)3(MoO4)8, from which a series of powder samples was prepared by a conventional solid-state reaction. The phase formation of the samples was investigated by X-ray diffraction which revealed the formation of a solid solution without a miscibility gap. Photoluminescence (PL) spectra and decay curves were recorded as a function of Tb3+ and Eu3+ concentration and temperature. It turned out that the external quantum efficiency of Eu3+ photoluminescence is between 30 and 80%, while the highest quantum yield is achieved for about 60% Tb3+. An increase of emission intensity can be realized by co-doping of Eu3+ and Tb3+. Moreover, the emission has a luminous efficacy of 275 lm Wopt−1 which is a distinct advantage over the widely applied Mn4+ activated fluorides. The time dependent photoluminescence as a function of Tb3+ concentration demonstrates the presence of an efficient energy transfer from Tb3+ to Eu3+. Temperature dependent PL measurements revealed that Li3Ba2(Tb1−xEux)3(MoO4)8 loses just 20% of PL efficiency up to 400 K. Therefore, the investigated phosphors are attractive for application in pcLEDs. It is finally demonstrated that the application of a Eu3+/Tb3+ co-doped ceramic disc is useful for the colour conversion of a blue emitting LED with a higher conversion rate compared to Li3Ba2(La1−xEux)3(MoO4)8.

Characterization of cerium-doped yttrium aluminium garnet nanopowders synthesized via sol-gel process

Abstract: In this work the sol-gel process was used to prepare Ce-doped yttrium aluminium garnet (Y 3 A l 5 O 12, YAG) samples. The synthesis products were characterized by infrared spectroscopy (IR), X-ray powder diffraction analysis (XRD), and transmission electron microscopy (TEM). The particle size and luminescence properties of synthesized samples were also determined. The XRD patterns of Y 3 A l 5 O 12:Ce samples showed that phase purity of garnets depends on the synthesis temperature and concentration of dopant. The YAG:Ce samples calcined at 1000°C showed the formation of single-phase YAG in the whole doping range (from 0 up to 10 mol% of Ce). However, during calcination at 1300°C the formation of CeO2 as an impurity phase at >4 mol% of Ce was observed. The mean particle size of Y 3 A l 5 O 12:Ce sample (4 mol% of Ce) synthesized at 1300°C was determined to be approximately 180–280 nm. The luminescence properties of Ce-doped YAG also depend on cerium concentration in the samples. The highest emission (λ ex ...

Fluorescent Nanoclays: Covalent Functionalization with Amine Reactive Dyes from Different Fluorophore Classes and Surface Group Quantification

Abstract: The ever increasing applications of fluorescence techniques in conjunction with the interest in enhanced detection sensitivities in bioanalysis, biosensing, and bioimaging are closely linked to the rational design of novel nontoxic fluorescent nanomaterials with improved brightness and stability that can be reproducibly synthesized from inexpensive starting materials in simple one-pot reactions and easily surface functionalized. This encouraged us to investigate the potential of the commercially available water-dispersible nanoclay Laponite RD with the empirical formula Na0.7(H2O)n{(Li0.3Mg5.5)[Si8O20(OH)4]}, forming 25 nm sized disk-shaped particles, as nanocarriers for different fluorophores. The Si–OH functions at the rims of these disks can be selectively grafted with 3-aminopropyldimethylethoxysilane (APES), thereby enabling subsequent coupling to amine-reactive molecules ranging from target-specific organic ligands and biomolecules to amine-reactive fluorescent labels. Here, we present different str...

Effects of enzyme addition on biogas and methane yields in the batch anaerobic digestion of agricultural waste (silage, straw, and animal manure)

Abstract: The anaerobic digestion (AD) of the organic fractions of solid wastes has been recognized as an economical and highly renewable resource for biogas production. The challenges lie in maximizing the biodegradation of lignocellulose-rich biomasses, which requires effective strategies to prevent the underutilization of feedstocks. Enzymatic treatments for lignocellulosic degradation have huge potential because of their highly versatile and selective compounds. Moreover, such treatments mimic natural processes and require low energy inputs. This study focuses on the batch AD of a variety of lignocellulosic substrates typically used in agriculture, such as silage, straw, and the manure of various animals. The effects of five different enzyme mixtures on the increase in the gas yields of batch AD were investigated. Biogas and methane yields were systematically obtained, and then the effects on total maximum gas yields and biodegradability were determined on the basis of organic dry matter. In almost all the assays between test days 5 and 15, the biodegradability was accelerated, leading to increases of 0.3%–21.1% in methane yields as appropriate to the substrate. However, after 60 days of testing, increases (−2.7%–9.4%) in the total maximum gas yields were not detectable in most cases. It was assumed that the main effects of the enzyme treatments would be faster degradability. Furthermore, the test series with hay and different enzyme dosages showed that a higher dosage does not necessarily result in a higher effect.