Crystal growth of niobates and borates. – Stoichiometric LiNbO3 (sLN) crystals doped with 1-2 at% rare-earth ions (Sm3+, Nd3+, Yb3+) have been grown by the Czochralski and the high-temperature top-seeded solution growth (HTTSSG) methods for IR spectroscopic experiments. An extra large prism (Fig. 1) has been prepared for tilted-front pumping ultra-short THz pulse generation using an sLN:Mg crystal grown by a semi-continuous feeding HTTSSG technique with a Mg-dopant concentration slightly above the photorefractive threshold. Li6Y0.99Pr0.01(BO3)3 (LYB:Pr) and β-barium borate (BBO) crystals have also been grown for spectroscopic and nonlinear optical applications.
Figure 1. Mg-doped stoichiometric LiNbO3 crystal prism prepared for high-intensity THz pulse generation.
Characterization of polaronic distortion in LiNbO3. — Polarization around trapped charges in oxides is assumed to be strongly confined but up to now experimental data on the distortion were lacking. We used a molecular probe (OH– ions) to determine the displacements of nearest-neighbour ions around O– small polarons in LiNbO3 crystals created by ps pump pulses in the blue region. Some of the holes were temporarily trapped at oxygens in the direct vicinity of impurity OH– ions which could be detected by the absorption of probe pulses in the infrared as a transient 3 cm-1 redshift of the stretcing vibration frequency of part of the OH– ions. The vibration was described by a Morse potential, the adjacent polaron by point-charge potential changes caused by the trapped charge and its shifted neighbours, both modifying the Morse potential. Assuming a ̴12% increase of the nearest Nb5+ neighbour distance from the trapping site (Fig. 2), agreement with the experimental redshift and earlier expectations could be achieved. On the other hand, assuming only a trapped hole without polaronic halo was found to result in a blueshift of the OH– frequency, contradicting experiment.
Figure 2. Electrostatic potential changes due to hole polaron trapping (in the origin), enlarged arrows indicating the polaronic displacements of neighbouring lattice ions.
Spectroscopy of lithium yttrium orthoborate (Li6Y(BO3)3, LYB) single crystals. – The electronic dipole orientation of the transition of Yb3+ ion pairs in 20 mol% Yb-doped LYB was shown to be parallel to the chain of rare-earth sites in the crystal lattice using high-resolution infrared absorption spectroscopy. Luminescence emission generated by coherent pair excitation has been successfully demonstrated by applying a high-intensity laser source. It was shown by SIESTA quantum-chemical calculations that the incorporation of Yb3+ ion pairs at nearest neighbour Y sites is energetically more favourable than for larger Yb-Yb distances. The spin-Hamiltonian tensors of isolated Yb3+ centres in LYB have been derived from angular dependent EPR spectra measured for 1 mol% Yb.
Using saturation spectroscopy in LYB:Er at 8 K the homogeneous linewidth, the population relaxation kinetics, and the magnetic-field-induced splitting of the spectral holes for the 4I11/2 – 4I13/2 – 4I15/2 transitions of Er3+ ions have been determined. The sensitivity of the spectral hole distances to the external magnetic field intensity is ̴20% lower in LYB:Er than found earlier in LiNbO3:Er. The same splitting and sensitivity was also confirmed by using high resolution FTIR absorption spectroscopy for a magnetic induction of 120 mT.
Analytical methods for environmental and advanced materials. – Airborne particulate matter (PM) over two rural roads of Piên (South Brazil), paved with ultramafic rocks, was analysed with EPMA, XRF and XRD to characterize elemental composition and crystallinity. Single-particle compositions indicated a few percentages of serpentine and amphibole in PM. The deposition efficiency of chrysotile in two principal segments of the human respiratory system was estimated using a lung deposition model. Almost half of the inhaled particles deposited in the respiratory system. Asbestos depositions were significant (~25 %) in lower airways, even under rest situation and nose breathing.
Interaction between bovine serum albumin (BSA) and silicon carbide (SiC), investigated in nanocrystals by fluorescence spectroscopic and simulation methods, was found to be both dynamic and static. A new model was applied to describe the dynamic quenching effect with huge bimolecular quenching constants. The average binding distance between BSA and SiC was derived from the fitted model parameters and Förster’s theory. Computer simulation of molecular docking identified a possible docking site of SiC in the surrounding of the tryptophan-134 residues of BSA.
High-resolution continuum-source graphite furnace atomic absorption spectrometry (HR-CS-GFAAS) methods were developed for the determination of the Al contaminant and the main component Si in SiC nanocrystals with a size-distribution of 1–8 nm dispersed in non-aqueous solution. Similar procedures starting from solid samples were optimized for the vaporization/atomization processes of Mg, evaporating lithium niobate optical single crystals doped with various amounts of Mg.