Lithium Iodate Research Articles

Twist-induced Casimir Attractive-Repulsive Transition Based on Lithium Iodate

Twist-induced Casimir Attractive-Repulsive Transition Based on Lithium Iodate

(H3O)Li2(IO3)3: crystal structure and IR spectrum

The synthesis, IR spectroscopy, thermal and UV-Vis transmittance of the new lithium iodate crystal: (H3O)Li2(IO3)3, were studied. The crystal structure of (H3O)+·2(Li)+· 3(IO3)- was determined by single-crystal X-Ray diffraction analysis at 100(2) K. It crystallizes in the monoclinic system (P21/n) with the parameters: a = 8.3266(12) Å, b = 10.9893(17) Å, c = 11.2472(17) Å, α = γ = 90°, β = 111.360(4)° and Z(Z') = 4(1). The structure contains a hydronium cation (H3O)+, three crystallographic independent trigonal pyramidal IO3 anions, and two independent cations (Li)+ coordinated each by four oxygen atoms 3(IO3)- at the apices of strongly deformed tetrahedrons. The research results have revealed the mechanisms of crystal formation and the characteristic absorption bands of functional groups, which are of scientific importance. The possibility of the existence of certain properties is also discussed.

Single Crystals of α–LiIO3 Doped with L–arginine and L–nitroarginine

One of the essential crystals for technology is the hexagonal modification of lithium iodate (α–LiIO3), which is endowed with nonlinear optical, pyroelectric, piezoelectric, acousto–optic properties. In recent years, a number of research groups studied physical and physiochemical properties of several single crystals (KDP, ADP, BTCA, ZTC) that were grown in the presence of various amino acids (L–alanine, L–glycine, L–arginine, L–lysine, etc.). In all these studies a positive effect on growth process and crystal quality is described for the amino acids being used as dopants in solutions. Based on the promising results of existing studies, in this work the effect of mixtures of the amino acids L–arginine and L–nitroarginine on α–LiIO3 single crystals is presented. Studies of IR spectrum, UV–Vis transmittance, thermal properties and nonlinear optical activity have shown that the optical quality and physicochemical properties of the crystal were improved in the presence of amino acid dopands. Our data indicates that second harmonic generation activity of the crystals of α–LiIO3 grown with L–arginine and L–nitroarginine dopants is 1.2 times higher than that of pure α–LiIO3.

Study of IR Spectroscopy of Crystalline Materials Structure Used in Laser Shutters

The IR absorption spectra of hexagonal crystals of lithium iodate α-LiIO3, used in laser shutters for ship wiring, where the quality, transparency and power of laser radiation are of great importance, are studied. The transmission spectra allowed us to determine the width of the crystal band gap 4.37 eV along the Z-axis (C6 [0001]) and 4.46 eV along the axis perpendicular to the Z axis. The activation energies and the wavelength of the vibrational centers associated with the vibrations of the H3O+, OH-, H2O groups, heavy D2O and semi-heavy molecules HDO are determined. It is established that the band 1450-1650 cm-1 is a superposition of at least two broad absorption maxima centered at ~1550 and ~1600 cm-1. It was experimentally established that the ratio of the absorption coefficients of these bands was ~1:1 (75:74 cm-1) for crystals grown in H2O, and ~2:1 (161:84 cm-1) – for crystals grown in D2O. This allows us to assume that in a lithium iodate crystal grown in D2O, the bands 1550 cm-1 and 1600 cm-1 correspond to the vibrations of the bound HDO and H2O molecules, the band 1150 cm-1 corresponds to the vibrations of heavy water molecules. The results of the study allowed us to propose a mechanism of transport and translational diffusion of protons and to determine the presence of heavy water molecules in crystalline materials, as well as to diagnose the quality of laser crystals.

Spectral diagnostics of vibrational centers in crystals with hydrogen bonds

In practical application of crystals in optoelectronics and laser technology it is necessary to know the direction of optical axes and types of oscillatory centers, which is a relevant and necessary condition. In this paper, the infrared spectra of transmission and absorption of hexagonal crystals of lithium iodate α-LiIO3, grown by open evaporation in H2O and D2O solutions, as well as natural lamellar crystals of phlogopite and muscovite monoclinic crystal are investigated. The band gap width of the investigated crystals is determined by transmission spectra. In the absorption spectra there were determined activation energy and wavelength of the oscillatory centers that are associated with the vibrations of protons, hydronium ions Н3О+, protium H+, OH groups and molecules HDO. The good correlation of the parameters of infrared spectra with the spectra of thermally stimulated depolarization currents and NMR spectra has shown. The possibility of diagnostics of types of oscillatory centers by means of infrared spectra is considered, which also allows to find out the direction of optical axes. The obtained results allow to use IR spectra to determine not only the types of vibrational centers, but also the presence of anisotropy of the crystal lattice of the studied crystals.

Development of Methods for Growing LiIO3 and Ba(NO3)2 Crystals as Materials for Laser Frequency Converters

New methods for growing LiIO3 and Ba(NO3)2 crystals have been developed. Barium nitrate crystals up to 12 × 12 × 100 mm3 in size and lithium iodate crystals up to 120 × 120 × 200 mm3 in size of necessary optical quality are obtained. The influence of рН on the morphology of Ba(NO3)2 growth faces is investigated. The data on the morphology of the {111} and {$$\bar {1}\bar {1}\bar {1}$$} faces of crystals grown at different solution acidities are obtained by atomic force scanning microscopy. The possibility of fabricating optical elements from LiIO3 crystals of ~100 × 100 × 100 mm3 in size is shown.

Spectral diagnostics of oscillation centers in crystals with hydrogen bonds

Practical application of crystals in optoelectronics and laser engineering requires the directions of optical axes and the types of oscillation centers be known, and this is an important and necessary condition. We have studied the infrared transmittance and absorption spectra of hexagonal lithium iodate α-LiIО3 crystals grown by open evaporation method in H2O and D2O solutions and natural lamellar monoclinic crystals of phlogopite and muscovite. The band gap of the test crystals has been determined from the transmittance spectra. The absorption spectra have provided information on the activation energy and wavelength of the activation centers related to the oscillations of protons, hydroxonium ions Н3О+, protium Н+, ОН- groups and HDO molecules. There has been a good correlation between the parameters of infrared spectra, thermally stimulated depolarization current spectra and nuclear magnetic resonance spectra. We have analyzed the possibility of oscillation center diagnostics based on infrared spectra which also allow determining the directions of optical axes. The experimental results confirm the possibility of using IR spectra for determining the type of oscillation centers and the presence of lattice anisotropy in test crystals.

Transmission Spectra and Optical Properties of a Mesoporous Photonic Crystal Based on Anodic Aluminum Oxide

Optical properties of a one-dimensional photonic-crystal film with a lattice period of ≈380 nm formed by electrochemical etching of an aluminum foil are investigated. Experimental data on the spectra of transmission and reflection in the region of the first, second, and third stop bands of anodic photonic crystal of aluminum oxide are compared with a theoretical dependence obtained from the well-known dispersion relation. The possibility of creating selective narrow-band optical filters based on mesoporous one-dimensional photonic crystals is analyzed. The conditions of enhancement of an electromagnetic field of laser radiation at 532 nm under normal incidence on a photonic-crystal surface are established. The possibility of generation of optical harmonics under the conditions of sharp increase in the effective field of the driving radiation in a mesoporous photonic crystal of anodic aluminum oxide filled with lithium iodate is analyzed.

First-principles based analysis of the piezoelectric response in [formula omitted]-LiIO3

The density functional theory combined with the modern theory of polarization is used to understand the microscopic origin of the piezoelectric effect in the hexagonal lithium iodate (α-phase). Calculations show that the e33 and e14 piezoelectric-stress elements respectively have the highest and the smallest value in agreement with the experimental evidences. This e33 value is a consequence of the lone pair orbital of the IO3- group. Further insights are obtained by the separation of the piezoelectric-stress into a purely electronic and ionic contributions. The latter contribution has been also decomposed into contributions from individual atoms, as well as contributions from phonon normal modes. The full set of elastic constants was computed, by means of which the piezoelectric-strain coefficients have been derived. These are discussed and compared to experimental data reported in literature.

Application potential of paratellurite and iodic acid crystals for acousto-optics in the Terahertz range

The possibility of applying paratellurite, iodic acid, and lithium iodate crystals in acousto-optics in the THz range has been investigated. The transparency windows of these crystals and their refractive indices in the THz range have been determined. The acousto-optic figures of merit of these materials are calculated for different acousto-optic interaction geometries.

Impact of impurities on the α-LiIO3 crystal growth: Technique for measuring the “dead zone”

Lithium iodate (α-LiIO3) single crystal is a promising nonlinear optical material, which used for efficient laser radiation conversion in the visible and near-IR regions. A technique for measuring the “dead zone” (ΔТ dz) of LiIO3 solutions has been developed; data on the impact of Fe(IO3)2, AgIO3, CsOH, H3PO4, and methyl methacrylate on the growth of the (100) face of α-LiIO3 crystals have been presented; and the dependences of the nucleation and motion of single steps on the degree of supersaturation have been measured. It is shown that the ΔТ dz value makes it possible to estimate the validity of solutions for growing α-LiIO3 crystals. The results of measuring the face growth rates and step velocities for KDP and α-LiIO3 crystals are compared.

First-principles characterization of the electronic and optical properties of hexagonal [formula omitted

Within the density functional theory framework, we investigate the structural, electronic, vibrational, dielectric, piezoelectric and optical properties of hexagonal lithium iodate, including some nonlinear response properties, like the nonlinear dielectric (electronic) susceptibility, the electro-optic tensor and the Raman tensor. Beyond the comparison with available experimental data and the associated analysis, we predict the values of several properties or characteristics of this material, e.g. the phonon frequencies with B symmetry, that are silent in both IR and Raman experiments, the Born effective charges, for which a detailed analysis is performed, Raman susceptibilities and the decomposition of the clamped electro-optic tensor in terms of the different modes. The agreement with available experimental results is reasonable to excellent, depending on the property. The lattice parameters and macroscopic dielectric constants agree to the experimental ones within 2%. The Kohn–Sham electronic bandstructure is predicted, but suffers from the well-known DFT band gap problem. Reflectivity spectra computed with the density functional perturbation theory are in qualitative and quantitative agreements with experiments for incident light along the two main hexagonal axes. The phonon frequencies at the Brillouin zone center are, in average, 5.74% apart from the experimental one. The previous assignment of Raman features is discussed, on the basis of our computed Raman spectra, including relative peak heights. Finally, this study confirms theoretically the large nonlinear coefficients d31 and d33 of −6.6pm/V and −7.5pm/V as well as its noteworthy piezoelectric and electro-optic properties that make this material remarkable.

Optical study of defects in lithium iodate α-LiIO_3

Photoluminescence (PL) in two broad bands at 2.95 and 2.6 eV in lithium iodate α-LiIO3 is associated with self-trapped excitons and native point defects (supposedly oxygen vacancies), respectively, based on the luminescence excitation spectra and the PL temperature dependence. Free charge carriers may be captured by two types of shallow traps with thermal activation energies of 0.14 and 0.21 eV: they are responsible for crystal darkening at temperatures below 200 K. Spontaneous emission of α-LiIO3 during cooling or heating at temperatures T<200  K is pyroluminescence, which occurs at dielectric breakdown in strong pyroelectric fields on the crystal surface and in its bulk as well as inside the channel defects.

Giant nonlinear optical activity in a plasmonic metamaterial

In 1950, a quarter of a century after his first-ever nonlinear optical experiment when intensity-dependent absorption was observed in uranium-doped glass, Sergey Vavilov predicted that birefringence, dichroism and polarization rotatory power should be dependent on light intensity. It required the invention of the laser to observe the barely detectable effect of light intensity on the polarization rotatory power of the optically active lithium iodate crystal, the phenomenon now known as the nonlinear optical activity, a high-intensity counterpart of the fundamental optical effect of polarization rotation in chiral media. Here we report that a plasmonic metamaterial exhibits nonlinear optical activity 30 million times stronger than lithium iodate crystals, thus transforming this fundamental phenomenon of polarization nonlinear optics from an esoteric phenomenon into a major effect of nonlinear plasmonics with potential for practical applications.

Photon coincidences in spontaneous parametric down-converted radiation excited by a blue LED in bulk LiIO_3 crystal

We report on experimental and numerical investigation of two-photon coincidence properties of the parametric spontaneous down-converted field excited by a high brightness blue LED in bulk lithium iodate crystal. Ratio of up to 11.5% of coincidence, which cannot be attributed to classical coincidences, to single photon counts was recorded at the outputs of multimode fibers, demonstrating well-preserved biphoton property. This result, combined with practically useful power of the source, suggests its possible application for a class of quantum experiments.

Sum-frequency mixing of radiation from two extended-cavity laser diodes using a doubly resonant external cavity for laser cooling of trapped ytterbium ions

Over 100 μW of continuous-wave tunable ultraviolet radiation at 370 nm is generated by the sum-frequency mixing of radiation from two extended-cavity laser diodes having powers of 60 mW at 822 nm and 8 mW at 671 nm in a lithium iodate crystal. The crystal is placed in an external cavity that enhances the powers of two fundamental beams simultaneously by approximately 40. This light source is successfully applied to the laser cooling of trapped ytterbium ions.

Dielectric studies of a α-LiIO3 crystals grown from neutral and alkaline solutions

The dielectric properties of lithium iodate crystals of the hexagonal modification grown from solutions with pH = 6.2, 7.1, and 11.0 in the frequency range from 25 Hz to 1 MHz at temperatures of 290–420 K were investigated. The temperature dependence of the imaginary part of the permittivity was found to exhibit clearly pronounced relaxation peaks originating from ionic mobility. The shift in the position of the relaxation maxima was used to calculate the activation energy and attempt frequency for mobile ions. The Cole-Cole diagrams revealed the existence of a spectrum of relaxation times. The presence of the specific feature in the ionic mobility of lithium iodate crystals grown from solutions with pH ∼ 7 was confirmed.

Investigation of the tunnel effect and dielectric parameters of α-LiIO3 crystals

Temperature and frequency spectra of tanδ, e′, and e″ of laser lithium iodate single crystals are investigated at temperatures in the interval 77–450 K and frequencies in the range 5–108 Hz. An analysis of these spectra and the Cole–Cole diagrams demonstrates tunneling of charge carriers and existence of relaxation oscillators of several types. The temperature interval for the tunnel effect is determined.

High-frequency broadband transducers of ultrasonic oscillations

The amplitude-frequency responses (AFRs) of ultrasonic oscillation transducers based on piezoelectric lithium iodate crystals of hexagonal modification and on magnetic soft ferrite powders are experimentally studied. The possibility to control the efficiency of magnetostriction powder transducers (MPTs) by variation in the value and orientation of the external magnetic field is shown. Results of measurements of the transformation efficiency for ferrites of various chemical compositions are presented.

Effect of fundamental radiation wave front astigmatism on the process of second optical harmonic generation in uniaxial crystals

Nonlinear processes of conversion of radiation with wave front astigmatism in nonlinear crystals of 6 and 3m symmetry are theoretically analyzed. Spatial-angular and energy structures of the second optical harmonic in lithium niobate and iodate crystals are investigated theoretically and experimentally.