THE meetings of the Institution of Electrical Engineers will be resumed in London during the second half of the current session if the present conditions continue. This applies to the ordinary meetings, informal meetings, meetings of the three technical sections and of the London Students’ Section. As regards activities in the provinces, the various committees will decide in the light of local conditions whether they are able to carry out programmes of meetings, visits and functions. The first ordinary meeting of the programme for the second half of the session will take place on January 25, at 6 p.m., when a discussion on “Fire-Fighting Equipment for Electrical Installations”, based on the E.R.A. Report on this subject, will be introduced by Messrs. H. W. Swann, J. Hacking and R. A. McMahon.

Institution of Electrical Engineers

This review covers publications from the second half of 2016 to the middle of 2017. Techniques and applications relevant to clinical and biological materials, foods and beverages are discussed in the text, presenting the key aspects of the work referenced, while the tables provide a summary of the publications considered. Further to the observations made in the 2017 Update, we have noted the increase in publications featuring nanomaterials. Topics relate to exposure and absorption of nanoparticles; potential toxicity, use as reagents in analytical methods and the analysis or characterisation of these materials. A growing number of techniques are being applied to bio-imaging. In particular, those involving XRF spectrometry are being applied to a large range of biological sample types. A gradual trend during recent years, that is now quite apparent, has been the increasing proportion of publications that involve foods and beverages compared with clinical samples. Not necessarily related, but another trend is the growing number of reports from laboratories in the Republic of China.

Atomic spectrometry update: review of advances in the analysis of clinical and biological materials, foods and beverages

With existing and emerging technologies urgently demanding the expansion of the laser wavelengths, high-performance nonlinear optical (NLO) crystals are becoming indispensable. Here, a prospective NLO crystal, Li2ZrTeO6, is rationally designed by the element substitution of Nb for Zr and Te from LiNbO3, which has been recognized as one of the most commercial NLO crystals. Li2ZrTeO6 with R3 symmetry inherits the structural merits of LiNbO3 (space group R3 c) and thus meets the requirements for NLO applications, including noncentrosymmetric crystal structure, moderate birefringence, and phase-matchability. Moreover, it can be exploited to achieve more outstanding optical damage resistant behavior (>1.3 GW cm-2), exceeding 22 times that of LiNbO3, which is more suitable for high-energy laser applications. Notably, this compound displays the widest IR absorption edge (7.4 μm) among all of the noncentrosymmetric tellurates reported so far. These excellent attributes suggest that Li2ZrTeO6 is a promising candidate for providing high NLO performance. The substitution of Nb for Zr and Te from LiNbO3 demonstrates a viable strategy toward the rational design of NLO crystals with anticipated properties.

Rational Design of a LiNbO3-like Nonlinear Optical Crystal, Li2ZrTeO6, with High Laser-Damage Threshold and Wide Mid-IR Transparency Window

Owing to the extraordinary richness of its physical properties, congruent lithium niobate has attracted multidecade-long interest both for fundamental science and applications. The combination of ferro-, pyro-, and piezoelectric properties with large electro-optic, acousto-optic, and photoelastic coefficients as well as the strong photorefractive and photovoltaic effects offers a great potential for applications in modern optics. To provide powerful optical components in high energy laser applications, tailoring of key material parameters, especially stoichiometry, is required. This paper reviews the state of the art of growing large stoichiometric LiNbO3 (sLN) crystals, in particular, the defect engineering of pure and doped sLN with emphasis on optical damage resistant (ODR) dopants (e.g., Mg, Zn, In, Sc, Hf, Zr, Sn). The discussion is focused on crystals grown by the high temperature top seeded solution growth (HTTSSG) technique using alkali oxide fluxing agents. Based on high-temperature phase equilibria studies of the Li2O–Nb2O5–X2O ternary systems (X = Na, K, Rb, Cs), the impact of alkali homologue additives on the stoichiometry of the lithium niobate phase will be analyzed, together with a summary of the ultraviolet, infrared, and far-infrared absorption spectroscopic methods developed to characterize the composition of the crystals. It will be shown that using HTTSSG from K2O containing flux, crystals closest to the stoichiometric composition can be grown characterized by a UV-edge position of at about 302 nm and a single narrow hydroxyl band in the IR with a linewidth of less than 3 cm−1 at 300 K. The threshold concentrations for ODR dopants depend on crystal stoichiometry and the valence of the dopants; Raman spectra, hydroxyl vibration spectra, and Z-scan measurements prove to be useful to distinguish crystals below and above the photorefractive threshold. Crystals just above the threshold are preferred for most nonlinear optical applications apart holography and have the additional advantage to minimize the absorption even in the far-infrared (THz) range. The review also provides a discussion on the progress made in the characterization of non-stoichiometry related intrinsic and extrinsic defect structures in doped LN crystals, with emphasis on ODR-ion-doped and/or closely stoichiometric systems, based on both spectroscopic measurements and theoretical modelling, including the results of first principles quantum mechanical calculations on hydroxyl defects. It will also be shown that new perspective applications, e.g., the generation of high energy THz pulses with energies on the tens-of-mJ scale, are feasible with ODR-doped sLN crystals if optimal conditions, including the contact grating technique, are applied.

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Growth, defect structure, and THz application of stoichiometric lithium niobate

The first alkali-metal vanadium iodate fluoride, CsVO2 F(IO3 ), with a novel 3D anionic framework, has been rationally designed and hydrothermally synthesized. The 3D [VO2 F(IO3 )]- framework in CsVO2 F(IO3 ) is built from 0D Λ-shaped cis-[VO3 F(IO3 )2 ]4- polyanions via corner-sharing of oxo anions and bridging of the iodate groups. CsVO2 F(IO3 ) displays both a strong second-harmonic generation (SHG) 1.1 times as strong as KTiOPO4 (KTP) under 2.05 μm laser radiation and high laser-induced damage threshold (LIDT) of 107.9 MW cm-2 . This work provides a new route to design SHG crystals with stable 3D anionic structures from low-dimensional structural building units.

CsVO2F(IO3): An Excellent SHG Material Featuring A Unprecedented 3D [VO2F(IO3)]⁻ Anionic Framework.

A simple and accurate spectroscopic method is proposed to determine the composition of LiNbO3 crystals close to the stoichiometric composition. The method is based on the evaluation of the vibrational spectrum of hydroxyl ions that are always present in air-grown crystals. The intensity ratio R=I3480/I3465 of two band components peaking at about 3480 and 3465 cm-1 changes linearly with Li2O content in the 49.7–50.0 mol % range. Thermal effects influencing the redistribution of hydroxyl ions among the different lattice sites have also been taken into account. On comparing the results with the calibration based on ultraviolet absorption edge measurements, an absolute accuracy of at about 0.02 mol % was obtained.

Determination of the crystal composition from the OH- vibrational spectrum in lithium niobate

Ultrasmall silicon carbide nanoparticles (SiC USNPs) are very promising biomarkers for developing new applications in diagnostics, cell monitoring or drug delivery, even though their interaction with biological molecules such as different proteins has not yet been investigated in detail. In this study, the biological behaviour of SiC USNPs in a medium modeling a living organism was investigated in detail through the dependence of the fluorescence on interactions between bovine serum albumin (BSA) and SiC USNPs. The interaction shows transient nanoparticle–protein associations due to the restricted diffusion behaviour of the nanoparticles in the vicinity of a protein. The transient association manifests in a complex fluorescence quenching mechanism where the dynamic component was dominated by Forster resonance energy transfer. By studying SiC nanoparticles of different sizes, it can be concluded that the transient effect is an ultrasmall nanoparticle behaviour.

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Identification of the binding site between bovine serum albumin and ultrasmall SiC fluorescent biomarkers.

Determination of silicon and aluminum in silicon carbide nanocrystals by high-resolution continuum source graphite furnace atomic absorption spectrometry.

LiNbO3 crystals grown from Na2O, Rb2O, and Cs2O containing fluxes were characterized by infrared and Raman spectroscopic methods. Pure, nearly stoichiometric crystals with 49.7–50.0 mol% Li2O content were obtained from solvents containing Rb2O and Cs2O, while Na2O entered the crystal as a dopant. The intensity ratio of two OH– absorption peaks at 3480 and 3465 cm–1 in thermal equilibrium was shown to be a useful and accurate parameter for the determination of the lithium content of pure LiNbO3 crystals close to the stoichiometric composition. From the remarkable change of both infrared and Raman spectra in crystals grown from Na2O solvent, the incorporation of Na on Li sites was assumed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

G. Dravecz

Papers

Growth, defect structure, and THz application of stoichiometric lithium niobate

Determination of the crystal composition from the OH- vibrational spectrum in lithium niobate

Identification of the binding site between bovine serum albumin and ultrasmall SiC fluorescent biomarkers.

Determination of silicon and aluminum in silicon carbide nanocrystals by high-resolution continuum source graphite furnace atomic absorption spectrometry.

Raman and infrared spectroscopic characterization of LiNbO3 crystals grown from alkali metal oxide solvents