Optical Properties Of Single Crystals Research Articles

Optical properties of single crystals and ceramics based on silver and thallium (I) halides in the range of 0.3–30.0 THz

This paper is devoted to single crystals and two-phase ceramics based on the TlBr0.46I0.54 – AgI, TlCl0.74Br0.26 – AgI, AgBr – AgI systems' properties study in the THz range of 0.3–30.0 THz. Plane-parallel windows were manufactured based on single crystals of composition 6, 13 mol.% AgI in TlBr0.46I0.54 and 3, 13, 25 mol.% AgI in AgBr, as well as based on two-phase ceramic composition 19, 25 mol.% AgI in TlBr0.46I0.54, 7, 14, 20, 27 mol.% AgI in TlCl0.74Br0.26 and 36 mol.% AgI in AgBr. The materials showed high transmission in the THz with an absorption band. Single crystals and ceramics of the TlBr0.46I0.54 – AgI system are transparent in the ranges 0.3–0.67 and 5–30 THz, which corresponds to wavelengths 447–1000 μm and 10–60 μm. The maximum transparency of the materials in the 5–30 THz range is 70 %, in the other ranges it reaches 40 %. Ceramics of the TlCl0.74Br0.26 – AgI system transmit THz radiation in the 0.3–0.85 and 6–30 THz (353–1000 μm and 10–50 μm) regions. The transparency reaches 60 % in the frequency range of 0.3–0.85 THz and 77 % in the range of 6–30 THz. In the case of AgBr – AgI system, the samples were transparent from 0.3 to 1 THz (300–1000 μm) with a maximum transparency of 77 % and from 5.55 to 30 THz (10–54 μm) with transparency up to 60 %. The attenuation coefficients for each system were quite low 0.03–0.8 cm−1 depending on the composition and system. The value of the coefficients decreased with decreasing emission frequency. The paper also compares the developed THz materials with known materials. A multiple characterization of each class of THz optical materials is given. As a result of the studies, it is found that the set of obtained properties makes the developed THz materials based on silver halides and monovalent thallium halides promising potential materials for application in THz devices and devices for a wide range of purposes.

Research progress of gadolinium aluminum garnet based optical materials

Gadolinium aluminum garnet is a compound with cubic structure composed of Al–O octahedron and Al–O tetrahedron. The chemical formula is Gd3Al5O12 (GdAG). In the field of optics, GdAG is an excellent matrix material, which has led researchers to explore in the direction of phosphors, scintillators and solid-state lasers. In view of many advances in recent years, the recent findings of GdAG and its derivatives in the above three directions are reviewed in this paper. For GdAG phosphors, this paper discusses the preparation technology of phosphors and the key factors affecting the fluorescence performance of phosphors. For GdAG scintillators and solid-state lasers, this paper discusses the factors affecting the porosity grain uniformity of transparent ceramics, and compares the optical properties of single crystal and optical ceramics. Finally, the problems in the synthesis and application of GdAG-based optical materials are discussed, and the future development direction is proposed.

Two‐Photon Absorption of Butterfly‐Shaped Carbonyl‐Bridged Twistarene

AbstractThe single crystals of a butterfly‐shaped carbonyl‐bridged twistarene 3 were obtained by slow diffusion of methanol into its chloroform solution. The single‐crystal structure analysis indicated that 3 crystallized in a triclinic space group (P‐1). The two‐photon absorption (TPA) and nonlinear optical properties of single crystal of 3 were investigated in the range of 400 nm ∼650 nm. This is the first example of the TPA study based on single crystals made from the carbonyl‐bridged twistarene. The corresponding TPA cross‐section was found to be 3.69 GM at 800 nm.

Nonlinear optical properties of single crystal of L-OOMHCL incorporation with Glycine Oxalic Acid (GOA) with high chemical stability for optoelectronic applications

In this report, a good nonlinear optical material with high criteria such as optical nonlinearity, chemical and thermal stability for life time system capability. The crystallographic orientation belongs to monoclinic crystal structure with the non-centrosymmetric space group, the prominent peaks were observed as (101), (112) and (300). The calculated lattice parameter values are, a = 6.21 Å, b = 3.67 Å, c = 12.12 Å, α = 90°, β = 103.21°, γ = 90° monoclinic space group of P21/n. A broad and strong peak at 3427 cm−1 was assigned to NH stretch, the OH and CH stretching of the compound were confirmed by the peaks present at 3043 cm−1 and 2934 cm−1. Moreover, the peaks at 1398 cm−1 represent the tartaric acid, another strong peak at 1261 cm−1 was assigned to CH2 twisting. In addition, the DTA curve shows a sharp endothermic peak at 109 °C, which corresponds to the melting point of the compound at this stage the sample lost its 20% of weights due to dehydration. From TGA curve, the L-OOMHCL crystal has good thermal stability up to melting point as there is no major weight loss below that temperature. However, it shows the more weight loss of 95% after the melting point due to the removal of volatile substances. Thus, it confirms the full degradation around 600 °C. The dielectric constant and the dielectric loss of L-OOMHCL crystal were carried out at three different temperatures 313 K, (40 °C) 333 K (60 °C) and 353 K (80 °C) for frequencies varying from 50 Hz to 5 MHz. Finally, we have calculated the refractive index value at the cutoff wavelength 214 nm and the 2.012 which is larger than unity, this results in greater development of polarization in the presence of dc electrical fields, hence leading to greater mobility.

Effect of oxygen dissolved in germanium on defect formation and optical properties of single crystals

Oxygen impurities and optical properties of Sb-doped germanium single crystals were investigated with Fourier transformed infrared spectrometry. The effect of oxygen on crystal structure was shown. The effects of annealing in the temperature range 623–723 K on the behavior of oxygen dissolved in germanium and on optical properties of single crystals have been investigated. It was found that annealing at lower oxygen partial pressure leads to the formation of thermal donors (TD) on the basis of dissolved oxygen atoms. It was established that TD formation and the decrease of unbound oxygen concentration is accompanied by the increase in temperature stability of the optical properties of crystals.

Nonuniform carrier density in Cd3As2 evidenced by optical spectroscopy

We report the detailed optical properties of Cd$_3$As$_2$ crystals in a wide parameter space: temperature, magnetic field, carrier concentration and crystal orientation. We investigate high-quality crystals synthesized by three different techniques. In all the studied samples, independently of how they were prepared and how they were treated before the optical experiments, our data indicate conspicuous fluctuations in the carrier density (up to 30%). These charge puddles have a characteristic scale of 100 $\mu$m, they become more pronounced at low temperatures, and possibly, they become enhanced by the presence of crystal twinning. The Drude response is characterized by very small scattering rates ($\sim 1$ meV) for as-grown samples. Mechanical treatment, such as cutting or polishing, influences the optical properties of single crystals, by increasing the Drude scattering rate and also modifying the high frequency optical response. Magneto-reflectivity and Kerr rotation are consistent with electron-like charge carriers and a spatially non-uniform carrier density.

Consolidation of the optoelectronic properties of CH3NH3PbBr3 perovskite single crystals

Ultralow trap densities, exceptional optical and electronic properties have been reported for lead halide perovskites single crystals; however, ambiguities in basic properties, such as the band gap, and the electronic defect densities in the bulk and at the surface prevail. Here, we synthesize single crystals of methylammonium lead bromide (CH3NH3PbBr3), characterise the optical absorption and photoluminescence and show that the optical properties of single crystals are almost identical to those of polycrystalline thin films. We observe significantly longer lifetimes and show that carrier diffusion plays a substantial role in the photoluminescence decay. Contrary to many reports, we determine that the trap density in CH3NH3PbBr3 perovskite single crystals is 1015 cm−3, only one order of magnitude lower than in the thin films. Our enhanced understanding of optical properties and recombination processes elucidates ambiguities in earlier reports, and highlights the discrepancies in the estimation of trap densities from electronic and optical methods.

Anisotropic electrodynamics of type-II Weyl semimetal candidate WTe2

We investigated the $ab$-plane optical properties of single crystals of ${\mathrm{WTe}}_{2}$ for light polarized parallel and perpendicular to the W-chain axis over a broad range of frequency and temperature. At far-infrared frequencies, we observed a striking dependence of the reflectance edge on light polarization, corresponding to anisotropy of the carrier effective masses. We quantitatively studied the temperature dependence of the plasma frequency, revealing a modest increase of the effective mass anisotropy in the $ab$ plane upon cooling. We also found strongly anisotropic interband transitions persisting to high photon energies. These results were analyzed by comparison with ab initio calculations. The calculated and measured plasma frequencies agree to within 10% for both polarizations, while the calculated interband conductivity shows excellent agreement with experiment.

Effect Of Annealing On The Behavior Of Oxygen Dissolved In Germanium And Optical Properties Of Single Crystals

<p>The annealing effect in the temperature range from 350 to 450 °С on the behavior of interstitial oxygen О<sub>i</sub> dissolved in germanium and on optical properties of single crystals has been investigated by Fourier transformed infrared spectrometry. It was found that oxygen band maximum of 843 cm<sup>–1</sup> shifted toward the 856 cm<sup>−1</sup> with oxygen concentration increasing after annealing at the oxygen partial pressure ranged from 1 to 10<sup>3</sup> Pа. The annealing at lower values led to the decrease of 843 cm<sup>–1</sup> band intensity due to the formation of thermal donors (TD) on the basis of dissolved oxygen atoms О<sub>i</sub>. It was established that TD formation and the decrease of unbound oxygen concentration affected optical properties of the crystals.</p>

Dispersion analysis with inverse dielectric function modelling

We investigate how dispersion analysis can profit from the use of a Lorentz-type description of the inverse dielectric function. In particular at higher angles of incidence, reflectance spectra using p-polarized light are dominated by bands from modes that have their transition moments perpendicular to the surface. Accordingly, the spectra increasingly resemble inverse dielectric functions. A corresponding description can therefore eliminate the complex dependencies of the dispersion parameters, allow their determination and facilitate a more accurate description of the optical properties of single crystals.

Relationship between Tribology and Optics in Thin Films of Mechanically Oriented Nanocrystals

Many crystalline dyes, when rubbed unidirectionally with cotton on glass slides, can be organized as thin films of highly aligned nanocrystals. Commonly, the linear birefringence and linear dichroism of these films resemble the optical properties of single crystals, indicating precisely oriented particles. Of 186 colored compounds, 122 showed sharp extinction and 50 were distinctly linearly dichroic. Of the latter 50 compounds, 88% were more optically dense when linearly polarized light was aligned with the rubbing axis. The mechanical properties of crystals that underlie the nonstatistical correlation between tribological processes and the direction of electron oscillations in absorption bands are discussed. The features that give rise to the orientation of dye crystallites naturally extend to colorless molecular crystals.

Ellipsometric Study of Anisotropy Permittivity of Hexagonal Manganites RMnO3 (R = Ho, Tm, Yb)

The optical properties of single crystals of the hexagonal manganites RMnO3 (R = Ho, Tm, Yb) have been investigated by spectroscopic ellipsometry in the spectral range 0.6-5.0 eV. The measurements show a strong anisotropy of the diagonal elements of the dielectric tensor. It has been demonstrated that the optical absorption edge for the polarization Ec was determined by the intense band of O(2p)Mn (3d) transition centered near 1.6 eV, whereas this band for the polarization Ec was strongly suppressed and shifted toward higher energies by 0.15-0.20 eV. The spectral dependences of the ε1(E) and ε2(E) for HoMnO3, TmMnO3 and YbMnO3 single crystals were qualitatively similar. The broad absorption band at E<1.0 eV clearly appears at the energies below the fundamental absorption edge of all of study compounds. It is possible, the origin of the near-infrared ε2(E) absorption is associated with 4f-4f transitions of R3+ ions.

Optical transmission of single crystal tellurium for application in acousto-opticcells

The optical properties of single crystals of tellurium (Te) are investigatedin order to develop acousto-optic (AO) devices operating in the longwaveinfrared spectral region. The optical transparency of carefully cut andpolished plates and large size samples of Te crystals was measured from 4 to24 µm. The absorption of ordinary and extraordinary polarized optical beams was measuredalong various directions in the crystal with respect to the optic axis. Using a10.6 µm CO2 laser the absorption coefficient for the best samples of Te was found to be0.07 cm − 1 for the ordinary andbetween 0.07 and 4.0 cm − 1 for the extraordinary polarized optical beam. Here, we also discuss the possible applicationof Te crystals in fabricating AO imaging filters.

Optical properties of single crystals of heavy lanthanide chlorides

Studies of heavy lanthanide chlorides may provide important information on the degree of Ln 3+–ligand bond covalency. Monocrystals of LnCl 3·6H 2O, where Ln = Dy, Ho and Er, were grown and spectroscopic investigations were performed at room temperature and at low temperatures down to 4.2 K in order to understand the nature of the Ln 3+–L bonds. The intensities of the electronic lines and the Judd–Ofelt parameters were calculated and compared with those obtained for chlorides of light lanthanides (i.e. Ce(III), Pr(III) and Nd(III)). Room temperature Raman and IR studies of the compounds under investigation were also performed. The relationship between hypersensitivity and covalency is discussed. The change of vibronic coupling strength along the lanthanide ion series does not modify monotonically. The ion-pair interactions are especially visible for the 5I 8 → 5F 2 and 5I 8 → 5F 3 transitions in the HoCl 3·6H 2O low temperature spectra.

Spectroscopy ofEu3+ions in congruent strontium barium niobate crystals

The optical properties of single crystals of strontium barium niobate, grown from the congruently melting composition and doped with different amounts of europium, are investigated. Absorption and emission spectra are measured in the visible and infrared spectral regions at different temperatures. From the spectra, conclusions on the structural sites can be drawn, revealing the major occupations of the B1 and B2 sites, and a minor one of the A2 site. The data are used to calculate crystal-field parameters for the mainly occupied site. A Judd--Ofelt analysis shows that the radiative quantum efficiency is approximately 70%. Furthermore, the influence of europium doping on the phase-transition temperature is determined.

Magnetic and optical properties of single crystals of transition metal doped ZnO

AbstractConsiderable effort has been devoted to the study of transition metal doped zinc oxide following various theoretical predictions of room temperature ferromagnetism in these materials. Near equilibrium growth techniques may be suitable for the production of dilute transition metal doped ZnO because the transition metal solubility in ZnO can be relatively high. This work reports on the optical, structural, and magnetic properties of single crystals of Co‐ and Mn‐doped ZnO grown by a modified melt‐growth technique. X‐ray diffraction reveals that the as grown crystals are pure single crystals with no second phases. Mn doping up to 5% results in an increase in c‐axis lattice parameter (5.207 Å to 5.211 Å), and X‐ray linewidths (78 arcsec to 252 arcsec) at doping levels of 5% Mn. Optical transmission shows distinct absorption spectra related to the color of the Zn1–x TMx O sample resulting from interatomic transitions within the divalent transition metal ion. Electron paramagnetic resonance confirms the divalent nature of the substitutional transition metal ions. Raman spectroscopy shows the predominantly the E2 (high) peak at 407 cm–1, but with increasing doping shows additional disorder‐related modes. The magnetic behavior reveals a paramagnetic behavior at all temperatures for both Mn‐ and Co‐doped ZnO up to transition metal doping levels of 5% and 3% respectively. The dominant exchange mechanism in the Mn‐ and Co‐doped ZnO crystals is found to be antiferromagnetic superexchange. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Coherence, incoherence, and scaling along thecaxis ofYBa2Cu3O6+x

The optical properties of single crystals of YBa_2Cu_3O_{6+x} have been examined along the c axis above and below the critical temperature (T_c) for a wide range of oxygen dopings. The temperature dependence of the optically-determined value of the dc conductivity (\sigma_{dc}) in the normal state suggests a crossover from incoherent (hopping-type) transport at lower oxygen dopings (x \lesssim 0.9) to more coherent anisotropic three-dimensional behavior in the overdoped (x \approx 0.99) material at temperatures close to T_c. The assumption that superconductivity occurs along the c axis through the Josephson effect yields a scaling relation between the strength of the superconducting condensate (\rho_{s,c}, a measure of the number of superconducting carriers), the critical temperature, and the normal-state c-axis value for \sigma_{dc} just above T_c; \rho_{s,c} \propto \sigma_{dc} T_c. This scaling relation is observed along the c axis for all oxygen dopings, as well as several other cuprate materials. However, the agreement with the Josephson coupling model does not necessarily imply incoherent transport, suggesting that these materials may indeed be tending towards coherent behavior at the higher oxygen dopings.

Structural and optical study on a single crystal of a novel fluorinated acridine

Within a new class of anthracene-like molecules, namely tetrafluoro-acridines, a systematic study of the structural and optical properties of single crystals of a prototypical member, 1,2,3,4-tetrafluoro-7(N,N)dimethyl-amino-acridine, is illustrated. Single crystals were grown by physical vapour transport using an inert gas flow as carrier, starting from a microcrystalline powder of the pure material. The crystal structure, determined by X ray diffraction, points out that the crystals are monoclinic with molecules stacked along the c axis. The results of atomic force microscopy on the ac face of a single crystal, at both low and molecular resolution, are consistent with the X-ray diffraction data. Preliminary results of the optical properties of the single crystal, in the unique configuration accessible due to the peculiar habit of the samples, are discussed.

Influence of exciton transfer on the optical cycle of α-PTCDA

The optical properties of single crystals of α-3,4,9,10-perylene-tetracarboxylic-dianhydride are analysed in terms of the transfer of Frenkel excitons coupled to an effective internal vibrational mode of the molecule, including the full microscopic crystal geometry with two molecules per unit cell. The resulting linear optical properties agree quantitatively with the refractive index and extinction coefficient measured on polycrystalline thin films, and the energy dependence of the anisotropic dielectric tensor is similar to ellipsometry data. A generalization of this model to Frenkel excitons propagating with different wave vectors results in a minimum of the exciton dispersion at the surface of the Brillouin zone. These low-lying states are obvious candidates for the origin of the red-shifted photoluminescence (PL), and the calculated radiative lifetime coincides with the measured decay time of the dominating PL channel at low temperature.

Structure and optical properties of single crystal of fluorene–thiophene oligomers

Solid-state optical properties of polymorph 2,7-(2-thienyl)-9,9-dihexylfluorene [TFT(C6) 2] and 2,7-di(2-thienyl)-9,9-cyclopentanefluorene [TFT] related to their crystal structure are reported. 3D phase of the first molecule displays a very peculiar arrangement, tetragonal system, where adjacent molecules cannot face to each other, due to fourfold alternating axis, therefore preventing close intermolecular interactions. The 3D packing of the second molecule shows a herringbone arrangement, where dimers are alternatively shifted. Both exhibit significant photoluminescence (PL), which changes in position and shape as a function of the solid state organization. Such different arrangements are related to different PL quantum yield values preliminarily determined.