No abstract available

No abstract available

[en] High resolution absorption spectra of a U³⁺(0.3%): Ba₂YCl₇ single crystal were recorded in the 4000-50 000 cm^-1 range at 7 K. The observed crystal-field levels were assigned and fit to the parameters of the simplified angular overlap model (AOM) as well as a semi-empirical Hamiltonian representing the combined atomic and one-electron crystal-field interactions. The starting values of the AOM parameters were obtained from ab initio calculations. The analysis of the spectra allowed the assignment of 65 crystal-field levels with a relatively small rms deviation of 25 cm^-1 and has shown that the AOM approach can predict quite well the B_q^k crystal-field parameters. The value determined for the crystal-field strength parameter, N_v, corresponds well with those determined for U³⁺ in other chloride single crystals. (authors)

[en] Single crystals of U⁴⁺:CsCdBr₃ were grown by the Bridgman-Stockbarger technique. It has been assumed, that U⁴⁺ ions are substituting two Cd²⁺ ions and possess the C_3v site symmetry. Thirty seven energy levels, located between 4000 and 25,000 cm^-1 and encompassing all but the ¹S₀ multiplet, were assigned from 7 K absorption spectra. The symmetry of the levels were determined on the basis of the observed small splitting of the Γ₃ doublets as well as by a comparison of low temperature absorption spectra of the U⁴⁺:CsCdBr₃ with that previously reported for U⁴⁺ in Cs₂UBr₆ and Cs₂ZrBr₆ single crystals. A crystal-field analysis was performed by fitting eight atomic (in the orthogonal formalism) and 6 crystal-field parameters to the experimental Stark levels with an r.m.s. deviation of 100 cm^-1. The obtained values of the Hamiltonian parameters are discussed and compared with those reported in previous analyses of U⁴⁺ ions. The relatively strong crystal field, resulting in N_v = 8530 cm^-1 proves that in the CsCdBr₃ crystals the U⁴⁺ ions are located at a high symmetry site

[en] Crystal-field splittings of Ho³⁺ ions in HoCl₃.6H₂O are re-analyzed in order to obtain a consistent and standardized crystal-field parameter (CFP) set. Experimental energy levels were fitted to Hamiltonian parameters representing the combined free-ion and crystal-field interactions for a 4f¹⁰ ion in the actual C₂ symmetry site. A relatively low r.m.s. deviation of 8.8 cm^-1 is achieved. The reliable starting values of the CFPs were obtained from superposition model analysis. The crystal-field strength, S, is significantly larger for HoCl₃.6H₂O (S = 262 cm^-1) than for Ho³⁺:LaCl₃ (S = 133 cm^-1) or Ho(C₂H₅SO₄)₃.9H₂O (S = 183 cm^-1), in which Ho³⁺ ion is coordinated by nine chlorine atoms or nine oxygen atoms from water molecules, respectively

[en] Nanotechnology can contribute to the development of innovative applications in the agriculture, food and feed sector by e.g. enabling improved delivery of nutrients or increased efficacy of agrichemicals. It is expected that applications will increase in the near future and may therefore become a relevant source of human exposure to nanomaterials (NM). To gain more up-to date information, RIKILT and the Joint Research Centre (JRC) were commissioned by the European Food Safety Authority (EFSA) to prepare an inventory of currently used and reasonably foreseen applications of NM in agriculture and food/feed production and carried out a review of regulatory aspects concerning NM in both EU and non-EU countries. An analysis of the information records in the inventory shows that nano-encapsulates, silver and titanium dioxide are the most frequent type of NM listed and that food additives and food contact materials are the most frequent types of application. A comparison between marketed applications and those in development indicates a trend from inorganic materials (e.g. silver) towards organic materials (nano-encapsulates, nanocomposites). Applications in novel food, feed additives, biocides and pesticides are currently mostly at a developmental stage. The review of EU and non-EU legislation shows that currently a few EU legal acts incorporate a definition of a nanomaterial and specific provisions for NM, whereas in many non-EU countries a broader approach is applied, which mainly builds on guidance for industry. (paper)

[en] The structural and optical properties of solution-processed Eu³⁺:BaY₂F₈ were characterized and compared to those of the sample synthesized by a solid-state reaction method. Precipitated from solution Eu³⁺:BaY₂F₈ has the fluorite (CaF₂) type of structure, which transforms completely into monoclinic form when powder is heated at 750 deg C. This temperature is also sufficient for entire elimination of hydroxyl groups. The intensities of f-f emission transitions of Eu³⁺ in BaY₂F₈ were analyzed in the frame of Judd-Ofelt model and the values of 1.23x10^-20 and 1.95x10^-20 cm² were determined for Ω ₂ and Ω ₄ intensity parameters. The experimental lifetimes of the ⁵D₀ and ⁵D₁ levels are equal to 8.4 and 2.3 ms, respectively. The quantum efficiency of Eu³⁺ in BaY₂F₈ was evaluated to be ∼35%