Intensity tunable optical limiting behaviour of an organic material 2-aminopyridinium succinate succinic acid single crystal

Journal of Materials Science: Materials in Electronics - A mixed solution of 2-aminopyridine and succinic acid, with a 1:1 molar ratio, was kept at room temperature to develop a 2-aminopridinium...     

Growth of optical grade yttrium oxide single crystal via ceramic technology

To sinter neodymium doped yttrium oxide (NDY) singe crystal several successive technologies: laser synthesis of NDY nanopowder, pulsed magnetic compacting of the powder and two stage vacuum sintering were used. With the help of abnormal grain growth samples of NDY single crystal were produced. Conditions that are necessary for abnormal grain growth in yttrium oxide as well to grow the optical grade single crystal are discussed.     

Optical,mechanical and transport properties of unidirectional grown l-tartaric acid bulk single crystal for non-linear optical application

Good optical quality bulk single crystal of l-tartaric acid has been grown by directional solidification crystal growth method from aqueous solution. Crystal of dimension 77 mm length and 12 mm diameter has been grown at a growth rate of 2.5 mm day⁻¹ which is the maximum size and growth rate achieved so far. The grown crystal was confirmed by powder XRD analysis and the presence of the functional groups in the crystal lattice was confirmed by Fourier transform infrared spectral analysis. Transmission spectral analysis shows that the crystal has more than 90% of transmittance in visible and near infrared region which exhibits the good optical quality of the crystal. The optical band gap was estimated to be 4.8 eV and it shows indirect optical transition. Thermal analysis shows the crystal to be thermally stable up to 172 °C and the load variation of the hardness has been explained on the basis of normal indentation size effect from microhardness study.     

Characterization and investigation of the mesogenic, thermo-morphologic and thermotropic properties of new chiral (S)-5-octyloxy-2-[{4-(2-methylbuthoxy)-phenylimino(methyl]phenol liquid crystalline compound

Synthesis, characterization and investigation of the mesogenic, thermo-morphologic and thermotropic properties of a new chiral liquid crystalline compound are presented in this work. This new compound has prolate molecules and exhibits the chiral smectic C* mesophase in a sufficiently large temperature interval. Two types of solid crystalline phases have been found in this compound. Typical textures and temperatures of the direct and reverse phase transitions, taking place in the compound, are given. Typical peculiarities for the first-order transition between the smectic C* mesophase and isotropic liquid have been observed.     

Optical properties of Nd-doped Ca3(VO4)2 single crystal fiber

Optical absorption and photoluminescence of Ca₃(VO₄)₂ single crystal grown by a floating-zone technique and containing Nd³⁺ ions were investigated. High absorption coefficients and broadening of most absorption bands are present at 300 K, while substructures in some of the same bands can be evidenced at 12 K. Most features of measured spectra are characteristic of random occupation of more than a single Ca²⁺ site by the Nd³⁺ ion and of distortions provoked by different charge compensation mechanisms involving oxygen vacancies promotion in the crystal lattice. Nd³⁺ optical properties were studied by using the Judd-Ofelt theory to calculate the spectral parameters relevant for laser applications.     

Nonlinear optical properties of p-(N,N-dimethylamino)dibenzylideneacetone doped polymer

A bis-chalcone derivative, p-(N,N-dimethylamino) dibenzylideneacetone was synthesized. Its third-order nonlinear susceptibility was determined to be as high as 10⁻¹² esu by employing single beam Z-scan and degenerate four wave mixing techniques using Nd:YAG 7 ns laser pulses at 532 nm. The compound was doped in to poly(methylmethacrylate) matrix and the third-order nonlinearity was investigated by using Z-scan technique. The nonlinear refractive index of the doped polymer is found to be negative, and its magnitude is of the order of 10⁻¹⁰ esu. The results show that the compound exhibits strong reverse saturable absorption and a good optical limiting property and hence may be used as a promising dopant material. The study on concentration dependence of nonlinear optical parameters has been presented.     

Low-temperature synthesis and optical properties of wurtzite ZnS nanowires

Single-crystal wurtzite ZnS nanowires have been synthesized via a facile solution route with polyethylene glycol-400 as inducing template at low temperature (170 °C). The as-prepared products have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and energy dispersive X-ray analysis (EDX). Raman and photoluminescence spectrum (PL) were used to investigate the optical properties of ZnS nanowires. The strong emission peak centered at 322 nm in PL spectrum could be attributed to the band to band transitions.     

Photoluminescence properties of single crystalline ZnO/CdS core/shell one-dimensional nanostructures

ZnO/CdS core/shell one-dimensional nanostructures were synthesized using ZnO nanorod arrays as templates, which were fabricated by a vapor transport process. CdS shells with various thicknesses were epitaxially grown on the ZnO nanorod arrays by metal organic chemical vapor deposition. Selected area electron diffraction measurement revealed that both ZnO cores and CdS shells were single crystalline growing along the c-axis. The photoluminescence properties of the ZnO/CdS core/shell nanostructures were also varied with different CdS shell thicknesses. A carrier transition process from ZnO to CdS was assumed to induce the enhancement of CdS photoluminescence.     

双羟乙氨基-硝基型偶氮分子的三阶光学非线性

设计并合成了5种综合性能较好的双羟乙氨基给体-硝基受体型偶氮化合物,它们分别具有DπA型和DπAπD型共轭结构.用Z-扫描方法研究它们的三阶非线性光学性质.实验结果表明双羟乙氨基给体和硝基受体组合与偶氮共轭链相连组成的分子具有较大的三阶非线性极化率.其中化合物5具有DπAπD型共轭结构,它包含两条从N,N-双羟乙氨基给体到硝基受体的共轭链,因此较大的分子内电荷转移使三阶极化率γ达到2.958×10-33esu,并且在化合物的共轭链中引入具有较低离域能的芳香杂环能增大三阶极化率.     

Growth and properties of benzil doped benzimidazole (BMZ) single crystals

In the present work, we have made an attempt to study the effect of benzil doping on the properties of benzimidazole single crystals. For this purpose we have grown pure and benzil doped benzimidazole single crystals by vertical Bridgman technique. The grown crystals were characterized by various characterization techniques. The presence of dopants confirmed by powder X-ray diffraction (XRD). Crystalline perfection of the grown crystals has been analysed by high-resolution X-ray diffraction (HRXRD). The transmittance, electrical property and mechanical strength have been analysed using UV-vis-NIR spectroscopic, dielectric and Vicker's hardness studies. The relative second harmonic generation efficiency of pure and doped benzimidazole crystals measured using Kurtz powder test.     

Single crystal growth,structure and properties of TlHgBr3

High-quality inclusion-free single crystals of ternary thallium mercury bromide, TlHgBr₃, were successfully grown by Bridgman–Stockbarger method. For the pristine surface of the TlHgBr₃ single crystal, X-ray photoelectron core-level and valence-band spectra were measured. The comparison on a common energy scale of the X-ray photoelectron valence-band spectrum of TlHgBr₃ and the X-ray emission Br Kβ₂ band, representing peculiarities of the energy distribution of the Br 4p states revealed that the main contribution of the valence Br p states, occurred in the upper portion of the valence band, with also their significant contributions in other valence band regions. It has been determined that TlHgBr₃ is a semiconductor with the bandgap energy value of E_g = 2.51 eV at 100 K. The E_g value decreased up to 2.44 eV when temperature increased to 300 K.     

Microstructure and stress rupture properties of single crystal superalloy CMSX-2 under high thermal gradient directional solidification

The interface morphologies of single crystal superalloy CMSX-2 were studied over a range of cooling rate with large variations in withdrawal speeds in directional solidification. A superfine cellular structure was obtained under both high thermal gradient up to 1000 K/cm and fast withdrawal rate up to 1 mm/s. The high rate directional solidification results in reduction in primary and secondary dendrite arm spacing, refinement of γ′ phase, reduced microsegregation of alloying elements and smaller size of γ-γ′ eutectics. The rupture life and plasticity of fine structure samples produced in high thermal gradient directional solidification increase significantly than that in conventional directional solidification process at 1323 K.     

χ measurements and optical limiting studies of 2-chloro-5-nitro-N′-[(1E)-phenylmethylidene] benzohydrazide with substituents

The nonlinear optical properties of hydrazones substituted with different donor groups were studied using single beam Z-scan technique with nanosecond laser pulses at 532 nm. The nonlinear response in these molecules was found to increase with increase in the donor strength of the substituted group. The χ⁽³⁾ value of these molecules is found to be of the order of 10⁻¹³ esu. The nonlinear refractive index (n₂) of the samples is found to be negative and the largest value of n₂ obtained for the strong donor-substituted molecule is −8.83 × 10⁻¹¹ esu. All samples show good optical limiting behavior at 532 nm. The best optical limiting behavior was observed with the molecule substituted by a strong electron donor.     

蓝紫光倍频晶体ZCTC晶体生长与透过性质研究

硫氰酸锌镉（ZnCd(SCN）4），简称ZCTC，是自行研发的一种蓝紫光倍频晶体。通过恒温蒸发溶液来生长ZCTC晶体，测量了KSCN和ZCTC溶液的透过率曲线，发现SCN^-基因是影响ZCTC晶体紫外截止波长的主要因素。研究还发现ZCTC晶体（100）面的透过度更高于（001）面，通过化学镀膜可以减少晶体表面反射损耗。ZCTC晶体经180℃，24h烘烤后，在300-800nm之间透过率明显下降。     

Structure,crystalline perfection,mechanical, second harmonic generation efficiency,laser damage threshold and piezoelectric properties of bis nicotinamidium bis D-tartrate 1.25-hydrate single crystals

Bis nicotinamidium bis D-tartrate 1.25-hydrate single crystals have been grown by slow evaporation solution growth technique. Single crystal X-ray diffraction study indicates that the grown crystal crystallizes in monoclinic system with space group P2₁. Crystalline perfection of the crystal has been evaluated by high resolution X-ray diffraction technique and it reveals that the crystal is free from structural grain boundaries. Mechanical stability of the crystal has been analyzed by Vickers microhardness measurement and it exhibits reverse indentation size effect. The second harmonic generation efficiency of the grown crystal has been checked and its value is 1.24 times that of potassium dihydrogen phosphate. The surface laser damage threshold for the crystal has been analyzed and its value is 0.644 GW/cm². Piezoelectric d₃₃ co-efficient for the crystal has been examined and its value is 29.8 pC/N.     

Investigation of structural,optical, and thermal properties of 2-amino-4,6-dimethylpyrimidine benzoic acid (2APB) single crystal for non-linear optical (NLO) applications

The 2-amino-4,6-dimethylpyrimidine benzoic acid (2APB) single crystal has been successfully grown by the slow evaporation method by using water as a solvent. The single-crystal X-Ray diffraction (SXRD) analysis gives knowledge about the structure and morphology of the 2APB crystal. The Powder X-ray Diffraction (PXRD) pattern of grinded 2APB crystal was compared with standard CIF file and the peaks were indexed with their corresponding miller indices (hkl). The crystalline perfection of the grown 2APB single crystal was analysed using high-resolution X-ray diffraction (HR-XRD) measurement. The various functional groups and their vibrational assignments were studied using the Fourier-transform infrared (FTIR) spectrum analysis. The 2APB crystal has a lower cut-off wavelength of 325 nm, which is evident from the UV–visible–NIR analysis. The defects and etch pit density of 2APB crystal were examined using chemical etching studies. The 2APB crystal was thermally stable up to 140 °C, which was evident from the thermogravimetric (TG) and differential thermal analysis (DTA). The photoconductivity analysis was carried out to calculate the photo and dark current values. The laser damage threshold (LDT) value was determined using a 532 nm Nd:YAG laser in single shot mode. The third-order non-linear optical (NLO) susceptibility (χ⁽³⁾) value was calculated from Z-scan technique, which involves open and closed aperture measurements.

     

Spectral properties of Tm:NaGd(MoO4)2 crystal

The Tm³⁺:NaGd(MoO₄)₂ crystal with dimensions of Φ 15 × 38 mm² was grown by Czochralski method. Polarized absorption and fluorescence spectra at room temperature were investigated. The absorption bands attributed to ³H₆ → ³H₄ transition have large absorption cross-sections, which are 3.99 × 10⁻²⁰ and 2.36 × 10⁻²⁰ cm² for σ- and π-polarization, respectively. The emission bands corresponding to the ³H₄ → ³H₆ transition are strong and broad with emission cross-sections of 1.33 × 10⁻²⁰ and 1.20 × 10⁻²⁰ cm² for σ- and π-polarization, respectively. The correlative full widths at half maximum are 35 nm for σ-polarization and 36 nm for π-polarization. The fluorescence lifetime for the ³H₄ → ³F₄ transition is 146 μs and the luminescent quantum efficiency is 76.8%.     

Effect of electron acceptor type on nonlinear optical absorption properties in the chiral polymers based on polybinaphthyls

Nonlinear optical absorption properties of two chiral polybinaphthyls with the same backbone but different electron acceptor hydroxyl and octoxy were studied in tetrahydrofuran solution. When excited by 100 fs 800 nm laser pulses, the up-converted fluorescence were observed and the intensities related to the different input irradiances were measured to confirm the two-photon excited fluorescence. The two-photon absorption coefficients were obtained as 4.82 cm GW⁻¹ and 12.36 cm GW⁻¹ with 100 fs pulses at 800 nm for two polymers, respectively. Under the excitation of 532 nm 38 ps pulse, it was found that the polymer with the side-chain of hydroxyl showed saturable absorption while the polymer with the side-chain of octoxy presented reverse saturable absorption. Their different nonlinear absorption behavior resulted from the fact that the ground-state absorption cross-section in the latter polymer was about 10 times larger than that of the former polymer while the excited-state absorption cross-section represented similar.     

Optical properties of β-FeSi2 single crystals grown from solutions

We studied the optical absorption, polarized reflectance (PR) and photoluminescence (PL) of β-FeSi₂ single crystals grown from solution. In low-absorption measurements, we found a phonon emission and absorption structure, which suggests an indirect transition. The exciton energy gap of 0.814 eV was determined from the absorption spectrum at 3.5 K. We also found a direct transition with the gap energy of 0.939 eV. PR measurements for Ea, Eb and Ec revealed the anisotropy of reflectivity of β-FeSi₂. We observed the PL with a peak wavelength of about 1.56 μm at 20 K.