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Sm3+-Doped and Eu3+/Sm3+-co-doped yttrium aluminium garnets (YAG) have been synthesized by an environmentally friendly sol–gel method. The results of X-ray diffraction (XRD) analysis of the powders sintered at 1000 °C showed the high purity of the end products with formation of monophasic compounds. The phase composition of the samples was also investigated by FTIR spectroscopy. The microstructural features of the polycrystalline samples were studied by scanning electron microscopy (SEM). The local environments of Eu3+ and Sm3+ activator ions in the garnet crystal structure compounds were investigated by nuclear magnetic resonance (NMR) and Raman spectroscopy. The luminescence properties were discussed using the results from photoluminescence (PL) study. The effective concentration of Sm in YAG was estimated and optimum ratio between two activators (Eu3+ and Sm3+) was analysed. The correlation between structural features and luminescence was determined. With a constant amount of samarium in Y2.9Sm0.1Al5O12:Eu garnet the strongest luminescence was determined in the sample with 1% of europium when characteristic excitation for europium was used. [ABSTRACT FROM AUTHOR]

Nd3+-Doped yttrium aluminium garnet and Eu3+–Nd3+-co-doped yttrium aluminium garnet were synthesized using an environmentally friendly sol–gel method at low temperatures. The results of X-ray diffraction (XRD) analysis of the powders sintered at 1000 °C showed the purity and formation of monophasic compounds. The phase composition and purity confirmation of the samples were also characterized via FTIR spectroscopy. Desirable microstructural features and particle size of phosphorous materials of the polycrystalline samples were studied via scanning electron microscopy (SEM). The local environments of Eu3+ and Nd3+ activator ions of the garnets structure compounds were investigated using nuclear magnetic resonance (NMR) spectroscopy. The local environments of the small number of substituted phosphorous ions (Eu3+ and Nd3+) in YAG were shown to critically influence optical properties. Structural features of garnets were found to correlate with their luminescence properties. The luminescence properties were characterized using the results from a photoluminescence (PL) study. Effective concentration of luminescent ion – Nd in YAG was, observed and the optimum ratio between two phosphorous (Eu3+ and Nd3+) was analysed. The transition among europium and neodymium phosphorus was determined. [ABSTRACT FROM AUTHOR]

Density functional theory together with statistical thermodynamics based on the equilibrium constants method and concept of orientational entropy were applied to reproduce the temperature dependences of 1H and 17O nuclear magnetic resonance (NMR) chemical shifts in liquid water. Despite a rather simple theoretical model, a satisfactory agreement between calculated NMR quantities and corresponding experimental data was found. By using only a single adjustable parameter of arbitrary directionality, we succeeded to imitate the first-order temperature effect for both (1H and 17O) NMR signals in the neat water. 1H and 17O magnetic shielding tensors of water molecules in various water clusters have been calculated using the density functional theory. The full geometry optimization was performed using Becke's three-parameter hybrid method and the Lee–Yang–Parr correlation functional (B3LYP) combined with 6-311++G** basis set. Magnetic shielding tensors have been calculated using the modified hybrid functional of Perdew, Burke and Ernzerhof, and the gauge-including atomic orbital approach was applied to ensure gauge invariance of the results. Solvent effects were taken into account by the polarized continuum model. [ABSTRACT FROM AUTHOR]

Abstract: The Raman spectra of 1-decyl-3-methyl-imidazolium bromide ([C10mim][Br]) aqueous solutions have been measured while continuously increasing the water content in the system (0–100%). Principal component (PC) and 2D Raman correlation (2DCOR) analysis has been carried out, the main attention concentrating to the region of O–H stretching vibrations at 3100–3800cm−1. The band structure has been resolved in the loadings on PC1 and PC2 as well as in 2DCOR spectra. It indicates the presence in the studied system of several nonequivalent states of water. Various states of water have been also revealed in the 1H NMR spectra. They have been assigned to non-bonded or weakly H-bonded water molecules, those involved in the fast isotropic reorientational motion as well as in the H-bond exchange processes and finally – water in the LC ionogel structures. The last contributes the 1H NMR line shape typical for anisotropic liquids with zero biaxiality (asymmetry) of magnetic shielding and the chemical shift anisotropy of ca 0.6ppm. The borders of the liquid crystalline (LC) ionogel phase have been determined using the concentration dependence of the integral intensities of Raman bands and the scores on PC1. [Copyright &y& Elsevier]

The solid-state 1 H, 31 P NMR spectra and cross-polarization (CP MAS) kinetics in the series of samples containing amorphous phosphate phase (AMP), composite of AMP + nano-structured calcium hydroxyapatite (nano-CaHA) and high-crystalline nano-CaHA were studied under moderate spinning rates (5-30 kHz). The combined analysis of the solid-state 1 H and 31 P NMR spectra provides the possibility to determine the hydration numbers of the components and the phase composition index. A broad set of spin dynamics models (isotropic/anisotropic, relaxing/non-relaxing, secular/semi-non-secular) was applied and fitted to the experimental CP MAS data. The anisotropic model with the angular averaging of dipolar coupling was applied for AMP and nano-CaHA for the first time. It was deduced that the spin diffusion in AMP is close to isotropic, whereas it is highly anisotropic in nano-CaHA being close to the Ising-type. This can be caused by the different number of internuclear interactions that must be explicitly considered in the spin system for AMP (I-S spin pair) and nano-CaHA (I N -S spin system with N ≥ 2). The P-H distance in nano-CaHA was found to be significantly shorter than its crystallographic value. An underestimation can be caused by several factors, among those - proton conductivity via a large-amplitude motion of protons (O-H tumbling and the short-range diffusion) that occurs along OH - chains. The P-H distance deduced for AMP, i.e. the compound with HPO 4 2- as the dominant structure, is fairly well matched to the crystallographic data. This means that the CP MAS kinetics is a capable technique to obtain complementary information on the proton localization in H-bonds and the proton transfer in the cases where traditional structure determination methods fail.

In the present work, three different Mn 2+ -doped calcium pyrophosphate (CPP, Ca 2 P 2 O 7 ) polymorphs were synthesized by wet co-precipitation method followed by annealing at different temperatures. The crystal structure and purity were studied by powder X-ray diffraction (XRD), Fourier-transform infrared (FTIR), solid-state nuclear magnetic resonance (SS-NMR), and electron paramagnetic resonance (EPR) spectroscopies. Scanning electron microscopy (SEM) was used to investigate the morphological features of the synthesized products. Optical properties were investigated using photoluminescence measurements. Excitation spectra, emission spectra, and photoluminescence decay curves of the samples were studied. All Mn-doped polymorphs exhibited a broadband emission ranging from approximately 500 to 730 nm. The emission maximum was host-dependent and centered at around 580, 570, and 595 nm for γ-, β-, and α-CPP, respectively., (© 2022. The Author(s).)