Luminescent and Magnetic Tb-MOF Flakes Deposited on Silicon

The synthesis of a terbium-based 2D metal–organic framework (MOF), of formula [Tb(MeCOO)(PhCOO)2] (1), a crystalline material formed by neutral nanosheets held together by Van der Waals interactions, is presented. The material can be easily exfoliated by sonication and deposited onto different substrates. Uniform distributions of Tb-2D MOF flakes onto silicon were obtained by spin-coating. We report the luminescent and magnetic properties of the deposited flakes compared with those of the bulk. Complex 1 is luminescent in the visible and has a sizeable quantum yield of QY = 61% upon excitation at 280 nm. Photoluminescence measurements performed using a micro-Raman set up allowed us to characterize the luminescent spectra of individual flakes on silicon. Magnetization measurements of flakes-on-silicon with the applied magnetic field in-plane and out-of-plane display anisotropy. Ac susceptibility measurements show that 1 in bulk exhibits field-induced slow relaxation of the magnetization through two relaxation paths and the slowest one, with a relaxation time of τlf ≈ 0.5 s, is assigned to a direct process mechanism. The reported exfoliation of lanthanide 2D-MOFs onto substrates is an attractive approach for the development of multifunctional materials and devices for different applications.

Assessment of the carotenoid pool using resonance Raman spectroscopy in pregnant women with preeclampsia

Objective. To assess the performance of resonance Raman spectroscopy in the evaluation of the carotenoid pool (antioxidants) in plasma of pregnant women with preeclampsia (PE). Patients and methods. We examined 60 pregnant women aged between 21 and 41 years, including 30 women with moderate PE, 18 women with severe PE, and 12 women with normal pregnancy. We used Raman spectroscopy to analyze serum specimens. Results. We evaluated diagnostic accuracy of Raman spectroscopy (as a method of express diagnostics) and measured normalized integrated Raman scattering intensity for carotenoids in women with moderate preeclampsia (5.0 ± 0.2), severe preeclampsia (6.1 ± 0.3) and normal pregnancy (10.1 ± 0.6). We also separated Raman luminescent spectra of plasma specimens obtained from patients in different groups: the accuracy of distinguishing between normal pregnancy and PE was 96%, while the accuracy of distinguishing between moderate PE and severe PE was 72%. Conclusion. Raman spectroscopy is a relatively simple, but highly effective method for rapid estimation of carotenoid levels in plasma of pregnant women with various grades of PE. Our findings suggest that Raman spectroscopy is a good method of preclinical diagnosis and prognosis of PE, particularly in women at high risk. Key words: carotenoids, discriminant analysis, preeclampsia, Raman spectroscopy, rapid diagnostics

Tunable photoluminescent properties of rare-earth co-doped (Na0.5Bi0.5)TiO3 ceramics by Pr3+ concentration

Lead-free piezoelectric ceramic materials have received extensive attention due to their potential application in new optoelectronic devices. The outstanding advantages of lead-free piezoelectric materials are nontoxicity and environmental-friendliness. Photoluminescence is one of the important properties of ceramics. This property is widely used in printing, testing materials, medical and other technologies. At the same time, materials with up-conversion luminescence can also be used to detect infrared light. Here, we had made [Formula: see text] and [Formula: see text] co-doped [Formula: see text] (NBT) ceramics. Photoluminescence properties of [Formula: see text] and [Formula: see text] co-doped NBT were studied. The structure of the doped ceramics was characterized by the X-ray diffraction pattern which shows that the doping had little effect on the ceramic structure. Studies on luminescent spectra show that [Formula: see text] has an inhibitory effect on the up-conversion luminescence of [Formula: see text], and a certain concentration of [Formula: see text] promotes the luminescence of [Formula: see text] in the mid-infrared region. Intensity of the up-conversion luminescence was substantially linear with the power of the excitation source. These findings are expected to improve the performance of the NBT-based optoelectronic devices.

Микрокристаллическая структура и светоизлучающие свойства 3C-SiC островковых пленок, выращиваемых на поверхности Si(100)

The crystal structure features and light-emitting properties of 3 C –SiC island films grown at decreased temperatures on the Si(100) surface by vacuum chemical epitaxy with the use of hydrogen-containing compounds are studied. The nucleation character and growth mechanisms of the nanocrystalline texture of microislands and the effect of elastic stresses accumulated on the surface of a growing carbide film on the shape of nucleating islands are traced by the methods of microscopy. The cathodoluminescence spectra from the surface carbidized Si layer and different areas of an individual 3 C –SiC island are compared. The possible mechanisms of the appearance of additional spectral lines shifted with respect to the major peak towards the red and ultraviolet spectral regions in the observed spectra of epitaxial structures are discussed. These emission bands were earlier revealed only in the luminescence spectra of SiC nanocrystallites embedded into different (most often SiO_2) matrices. The comparative analysis of the behavior of lines in the observed luminescent spectra has not revealed any appreciable size effect of formed surface nanocrystallites on their positions, but demonstrated their evident dependence on the oxygen content at the 3 C –SiC layer/silicon substrate interface.

Energy Transfer between Ce3+-Dy3+ in Ca2Al2SiO7: Ce3+, Dy3+ Phosphor

Ce3+ and Dy3+ ions doped Ca2Al2SiO7 (CAS) phosphors were prepared by the solid-state reaction at 12800C for 1h. X-ray diffraction patterns confirmed a tetragonal crystalline structure. The luminescent spectra of CAS: Ce3+, Dy3+ phosphors consist a board band with peaking at 420 nm corresponding to the luminescence of Ce3+ ions and narrow lines of Dy3+ ions. The energy transfer from Ce3+ ion to Dy3+ ion is presented and discussed