TY - JOUR A1 - Dreßler, Martin A1 - Nofz, Marianne A1 - Malz, Frank A1 - Pauli, Jutta A1 - Jäger, Christian A1 - Reinsch, Stefan A1 - Scholz, G. T1 - Aluminum speciation and thermal evolution of aluminas resulting from modified Yoldas sols N2 - Aluminas resulting from sols prepared via a modified Yoldas procedure were studied with differential thermal analysis (DTA), differential thermal gravimetrie (DTG), 27Al nuclear magnetic resonance (27Al MAS NMR) and X-ray diffraction (XRD) concerning their thermal properties, aluminum speciation and phase content. Hydrolysis of aluminum-sec-butoxide in aluminum nitrate solutions allowed to prepare stable sols with varying NO3-/Al molar ratios, solids contents and pH values. Resulting sols contained different aluminum species including also Al13 polycations. Sol preparation conditions also determined aluminum speciation in solid products obtained after thermal treatments of gels obtained from these sols. Al13 polycations and AlO5 species were found to play an important role for thermally induced transformation from amorphous products via eta-Al2O3 to alpha-Al2O3. Intermediately formed eta-Al2O3 promotes the phase transformation to alpha-Al2O3. KW - Alumina KW - Modified Yoldas sols KW - 27Al nuclear magnetic resonance KW - Differential thermal analysis KW - X-ray diffraction PY - 2007 DO - https://doi.org/10.1016/j.jssc.2007.06.018 SN - 0022-4596 SN - 1095-726X VL - 180 IS - 9 SP - 2409 EP - 2419 PB - Elsevier CY - San Diego, Calif. AN - OPUS4-16189 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hatami, Soheil A1 - Würth, Christian A1 - Kaiser, Martin A1 - Leubner, S. A1 - Gabriel, S. A1 - Bahrig, L. A1 - Lesnyak, V. A1 - Pauli, Jutta A1 - Gaponik, N. A1 - Eychmüller, A. A1 - Resch-Genger, Ute T1 - Absolute photoluminescence quantum yields of IR26 and IR-emissive Cd1-xHgxTe and PbS quantum dots - method- and material-inherent challenges N2 - Bright emitters with photoluminescence in the spectral region of 800–1600 nm are increasingly important as optical reporters for molecular imaging, sensing, and telecommunication and as active components in electrooptical and photovoltaic devices. Their rational design is directly linked to suitable methods for the characterization of their signal-relevant properties, especially their photoluminescence quantum yield (Φf). Aiming at the development of bright semiconductor nanocrystals with emission >1000 nm, we designed a new NIR/IR integrating sphere setup for the wavelength region of 600–1600 nm. We assessed the performance of this setup by acquiring the corrected emission spectra and Φf of the organic dyes Itrybe, IR140, and IR26 and several infrared (IR)-emissive Cd1-xHgxTe and PbS semiconductor nanocrystals and comparing them to data obtained with two independently calibrated fluorescence instruments absolutely or relative to previously evaluated reference dyes. Our results highlight special challenges of photoluminescence studies in the IR ranging from solvent absorption to the lack of spectral and intensity standards together with quantum dot-specific challenges like photobrightening and photodarkening and the size-dependent air stability and photostability of differently sized oleate-capped PbS colloids. These effects can be representative of lead chalcogenides. Moreover, we redetermined the Φf of IR26, the most frequently used IR reference dye, to 1.1 × 10-3 in 1,2-dichloroethane DCE with a thorough sample reabsorption and solvent absorption correction. Our results indicate the need for a critical reevaluation of Φf values of IR-emissive nanomaterials and offer guidelines for improved Φf measurements. PY - 2015 DO - https://doi.org/10.1039/c4nr04608k SN - 2040-3364 SN - 2040-3372 VL - 7 IS - 1 SP - 133 EP - 143 PB - RSC Publ. CY - Cambridge AN - OPUS4-32408 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ramirez Caro, Alejandra A1 - Pauli, Jutta A1 - Mota, Berta A1 - Crasselt, Claudia A1 - Artemeva, Elena A1 - Schmidt, Wolfram A1 - Resch-Genger, Ute T1 - A Spectroscopic Study of the Superplasticizer Effect on Early Cement Hydration N2 - Organic/inorganic mixtures were prepared from ordinary Portland cement (OPC), water (w/c 0.22), a fluorescent dye in aqueous solution (stable at alkaline pH; BAM-I), and two different comb shape polycarboxylates (PCEs), i.e., high charge (PCE-HC) and low charge (PCE-LC), respectively. Rheological and calorimetric measurements were performed prior to optical studies in order to select PCE concentrations. Absorption and fluorescence spectroscopy of the system OPC + BAM-I (CBAM-I) revealed maxima of dye BAM-I located at 645 nm and 663 nm, respectively. In presence of PCE-HC and PCE-LC, these mixtures displayed a small red shift in reflectance and a faster decrease in intensity compared to studies with CBAM-I; however, only slight differences were observed between the different PCEs. With time, all systems exhibited a decrease in intensity of BAM-I in absorption/reflectance and emission. This could be caused by dye adsorption and possibly decomposition when in contact with cement particles or hydration products. T2 - The Sixth International Symposium on Nanotechnology in Construction (NICOM6) CY - Hong Kong, China DA - 02.12.2018 KW - Cement KW - Optical Spectroscopy KW - Dye KW - Hydration PY - 2018 SP - 1 EP - 9 AN - OPUS4-49378 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ramirez Caro, Alejandra A1 - Mota, Berta A1 - Artemeva, E. A1 - Pauli, Jutta A1 - Schmidt, Wolfram A1 - Resch-Genger, Ute T1 - A spectroscopic study of the superplasticizer effect on early cement hydration N2 - Organic/inorganic mixtures were prepared from ordinary Portland cement (OPC), water (w/c 0.22), a fluorescent dye in aqueous solution (stable at alkaline pH; BAM-I), and two different comb shape polycarboxylates (PCEs), i.e., high charge (PCE-HC) and low charge (PCE-LC), respectively. Rheological and calorimetric measurements were performed prior to optical studies in order to select PCE concentrations. Absorption and fluorescence spectroscopy of the system OPC + BAM-I (CBAM-I) revealed maxima of dye BAM-I located at 645 nm and 663 nm, respectively. In presence of PCE-HC and PCE-LC, these mixtures displayed a small red shift in reflectance and a faster decrease in intensity compared to studies with CBAM-I; however, only slight differences were observed between the different PCEs. With time, all systems exhibited a decrease in intensity of BAM-I in absorption/reflectance and emission. This could be caused by dye adsorption and possibly decomposition when in contact with cement particles or hydration products. T2 - 20. Internationale Baustofftagung CY - Weimar, Germany DA - 12.09.2018 KW - Optical spectroscopie KW - Cement hydration KW - Dyes PY - 2018 SN - 978-3-00-059950-7 VL - 20 SP - 1 EP - 6 PB - F.A. Finger-Institut für Baustoffkunde CY - Weimar AN - OPUS4-46277 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Nofz, Marianne A1 - Pauli, Jutta A1 - Dreßler, Martin A1 - Jäger, Christian A1 - Altenburg, Wolfgang T1 - 27Al NMR Study of Al-Speciation in Aqueous Alumina-Sols N2 - A new method of preparing concentrated alumo-sols, the hydrolysis of Al-tri-sec-butylate in acidic aqueous media at 85°C, was studied in detail by varying the H2O/Al- and NO3 -/Al-ratios in wide ranges. The components of the sols were characterized by 27Al NMR spectroscopy. The pH-value depends on both the chosen H2O/Al- and NO3 -/Al-ratio and on the aging time of the sols and reflects the composition of the sols. Al13 polycations were detected in sols with a pH-value between 3.0 and 3.7. As a new result its presence was shown by NMR below 3.4. The Al13 content of the sols increased with pH and the maximum fraction of Al13 polycations was detected in the sol with the highest pH (3.7). Nearly 65% of the entire aluminium content of this solution is bound in the Al13 polycations. Hence, a new synthetic method for the preparation of Al13 ions containing sols was developed. Aging studies of the sols showed, that the Al13 polycations were more stable in solutions with higher pH-value. Al13 polycations were detected after an aging time of four months only in sols with a pH-value of 3.7. Tempering the aged sols at 40° to 80°C caused formation of Al13 and also of Al30 polycations. KW - Alumo-sol KW - Al13 polycations KW - Al-27 NMR spectroscopy PY - 2006 SN - 0928-0707 SN - 1573-4846 VL - 38 IS - 1 SP - 25 EP - 35 PB - Kluwer Academic Publ. CY - Dordrecht AN - OPUS4-12350 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -