Growth and Characterization of Single Crystals ofl-Histidine Hydrochloride Monohydrate for Nonlinear Optical Applications

In the present study, we have focused on the growth of semi-organic single crystals, as they play a vital role in the generation of a terahertz pulse and its potential applications. The single crystals ofl-histidine hydrochloride monohydrate (LMHCL) were grown by slow evaporation solution growth by using deionized water as a solvent in a controlled atmosphere. Good quality crystals of the required size were obtained within 2 weeks. To estimate the lattice dimensions and get the structural information, powder x-ray diffraction (PXRD) study was performed in which we have found that the crystal belongs to the orthorhombic crystal system with space groupP2(1)2(1)2(1). The functional groups and the corresponding vibrational mode were confirmed using Fourier transform infrared (FTIR) and Raman spectroscopy, respectively. To study the optical properties UV-Vis transmission spectrum and photoluminescence (PL) were recorded. It was observed that the single crystal has a high value of transmission over a long range of wavelength which signifies that the crystal is a good candidate for nonlinear optical (NLO) applications. The UV cut-off wavelength is found to be 236 nm. The grown single crystals were studied by time-domain terahertz spectroscopy (THz-TDS) for photonic applications and the refractive indices were calculated and it is found that the refractive index is nearly equal to 3.4

高強度モノサイクルTHzパルスで駆動されたアミノ酸結晶の非調和振動

京都大学0048新制・課程博士博士(理学)甲第15632号理博第3578号新制||理||1522(附属図書館)28169京都大学大学院理学研究科物理学・宇宙物理学専攻(主査)准教授 中 暢子, 教授 高橋 義朗, 准教授 松田 一成学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDA

Ultrafast pump-probe spectroscopy studies of CeO2 thin film deposited on Ni-W substrate by RF magnetron sputtering

This study presents the first investigation of rapid dynamical processes that occur in pure CeO2 thin film, using ultra fast pump-probe spectroscopy at room temperature. For this purpose we have used a single (200) oriented CeO2 film deposited on biaxially textured Ni-W substrate by RF magnetron sputtering technique. The ultrafast transient spectra show initial sharp rise transition followed by an exponential photon decay. This rise time is about 10 ps irrespective of the probe wavelengths range 500-800 nm. The initial decay constant (tau) at 500 nm probe wavelength is found to be 171 ps, while at 800 nm probe wavelength it is 107.5 ps. The ultrafast absorption spectra show two absorption peaks at 745 and 800 nm, and are attributed to the electronic transitions from F-2(7/2)-F-2(5/2) and S-1(0)-F-1(3) respectively. The relatively high intensity absorption peak at 745 nm indicates dominant f-f electronic transition. Further, the absorption peak at 745 nm splits into two distinct peaks with respect to delay time, and is attributed to the charge transfer in between Ce4+ and Ce3+ ions. These results indicate that CeO2 itself is a potential candidate and can be used for optical applications

Synthesis and ultrafast spectroscopic study of new [6,6]methanofullerenes

Ultrafast transient absorption and terahertz spectroscopic studies have been performed on new [6,6] methanofullerenes synthesized by the reaction of diazomethane (generated in situ from their hydrazone precursor) with fullerene[60] via our eco-friendly methodology, i.e., amine-assisted 1,3 dipolar cycloaddition (AACA). Synthesized materials have been characterized by different spectroscopic techniques for their structure establishment, including terahertz spectroscopy to study changes in spectra on functionalization. Attachment of different types of functional groups on exohedral chains resulted in band gap tuning. Photoinduced charge generation and charge separation studies have been performed to understand the charge carrier dynamics in a methanofullerene : P3HT mixture. Efficient charge separation efficiency is observed in both the acceptors on mixing with P3HT, making them potential acceptor materials in organic solar cells. High photoconductivity calculated by terahertz time domain spectroscopy of these new fullerene derivatives can also be exploited in other organic electronic devices

Influence of Eu substitution on structural, magnetic, optical and dielectric properties of BiFeO3 multiferroic ceramics

Eu substituted BiFeO3 (Bit(1-x)Eu(x)FeO(3); x=0-0.15) polycrystalline ceramics were synthesized by a solid state reaction method. Rietveld refinement of X-ray diffraction patterns reveals that samples crystallize in R3c structure for x 0.12-0.15. The magnetic measurements show weak ferromagnetic nature of Eu substituted BiFe03 samples due to ferromagnetic coupling between Eu3+ and Fe3+ ions. The remnant magnetization is found to increase from 0.0003 emu/g for x=0.00 to 0.087 emu/g for x=0.15. The gradual change in line shape of electron spin resonance spectra has been attributed to local distortion induced by Eu substitution. UV visible absorption spectra in the spectral range 1.12-3.5 eV were dominated by two charge transfer transitions and two doubly degenerate d d transitions. The optical band gap is found to decrease from 2.25 to 2.16 eV with increasing Eu concentration. Improved dielectric properties with enhancement in frequency independent region of dielectric constant and loss have been observed

Structural modification and enhanced magnetic properties with two phonon modes in Ca-Co codoped BiFeO3 nanoparticles

Bi1-xCaxFe1-xCoxO3 nanoparticles with x=0.0, 0.05, 0.10 and 0.15 were successfully synthesized by cost effective tartaric acid based sol gel route. The alkali earth metal Ca2+ ions and transition metal Co3+ ions codoping at A and B-sites of BiFeO3 results in structural distortion and phase transformation. Rietveld refinement of XRD patterns suggested the coexistence of rhombohedral and orthorhombic phases in codoped BiFeO3 samples. Both XRD and Raman scattering studies showed the compressive lattice distortion in the samples induced by codoping of Ca2+ and Co3+ ions. Two-phonon Raman spectra exhibited the improvement of magnetization in these samples. X-ray photoelectron spectroscopy (XPS) showed the dominancy of Fe3+ and Co3+ oxidation states along with the shifting of the binding energy of Bi 4f orbital which confirms the substitution Ca2+ at Bi-site. The magnetic study showed the enhancement in room temperature ferromagnetic behavior with co-substitution consistent with Rama analysis. The gradual change in line shape of electron spin resonance spectra indicated the local distortion induced by codoping

Flexible and Polarization Independent Miniaturized Double-Band/Broadband Tunable Metamaterial Terahertz Filter

In this paper, the design of a double-band terahertz metamaterial filter with broadband characteristics using a single conducting layer is presented. The design uses a structured top metallic layer over a polyimide material. The proposed design has achieved broadband band-pass transmission characteristics at the resonances of 0.5 THz and 1.65 THz, respectively. The 3-dB bandwidths for these two resonances are 350 GHz and 700 GHz, respectively, which indicates that dual-band resonance with broadband transmission characteristics was obtained. The design has achieved the same transmission characteristics for two different orthogonal polarizations, which was confirmed using numerical simulation. The design was tested for a different angle of incidences and it was observed that this results in angle-independent transmission behavior. In addition, for obtaining tunable resonant behavior, the top conductor layer was replaced by graphene material and a silicon substrate was added below the polymer layer. By varying the Fermi level of graphene, modulation in amplitude and phase was observed in numerical simulation. The physical mechanism of double-band behavior was further confirmed by surface current distribution. The proposed design is simple to fabricate, compact, i.e., the size is λ0/8, and obtained dual-band/broadband operation

Comparative charge transfer studies in nonmetallated and metallated porphyrin fullerene dyads

Single material organic solar cells become an interesting area of research to overcome the challenges with efficient charge separation efficiencies in conventional organic solar cells. In this article, we have synthesized nonmetallated and metallated porphyrin-fullerene dyad materials (H2P-C60 and ZnP-C60, respectively) with simple structure, comprehensively studied their charge transfer mechanism, and established a proof of concept that nonmetallated porphyrin-fullerene dyads are better candidates to be used in organic solar cells compared with metallated dyads. Absorption and electrochemical analysis revealed the ground state electronic interactions between donor-acceptor moieties in both types of dyads. Driving force (-Delta G(ET)(o)) for intramolecular electron transfer process was calculated by first oxidation and reduction potentials of dyads. The excited state electronic interactions were characterized by time-resolved fluorescence and pump-probe transient absorption experiments. Strong fluorescence quenching of porphyrin along with reduced lifetimes in dyads due to deactivation of singlet excited states by photoinduced charge transfer process between porphyrin/Zn-porphyrin core and fullerene in different polarity solvents was observed. Transient absorption spectroscopy was also applied to identify the transient spectral features, ie, cationic (H2P(+)/ZnP+) and anionic (C-60(-)) radicals formed because of the charge separation in both types of dyads. Finally, organic solar cell device was also fabricated using the dyads. We obtained higher V-oc, J(sc), and fill factor in single material organic solar cell using H2P-C60 compared to previous reports

Real-Time Two-Dimensional Spatiotemporal Terahertz Imaging Based on Noncollinear Free-Space Electrooptic Sampling and Application to Functional Terahertz Imaging of Moving Object

We review 2-D spatiotemporal (2D-ST) terahertz (THz) imaging based on noncollinear free-space electrooptic sampling and its application to THz reflection tomography, THz spectral imaging, and THz spectral computed tomography (CT). 2D-ST #x00A0;THz imaging enables high-speed image acquisition at much higher rates than previously. Two-dimensional THz reflection tomography was effective for visualizing the internal structure of a moving paint film. A THz color scanner demonstrated the potential of rapid nondestructive inspection of moving pharmaceutical tablets. A THz spectral CT system using real-time line projection of a THz beam was effectively applied to a continuously rotating object. 2D-ST THz imaging enables functional THz imaging of moving objects in various practical applications

Structural, magnetic, dielectric and optical properties of nickel ferrite nanoparticles synthesized by co-precipitation method

Nickel ferrite nanoparticles were synthesized by wet chemical co-precipitation method and the corresponding temperature dependent structural, magnetic and optical properties of these nanoparticles have been investigated. X-ray diffraction patterns show the single phase cubic spinal crystal structure belonging to the space group Fd3m. The average crystallite size varies in the range 8-20 nm with varying sintering temperature. Raman spectroscopy exhibits a doublet-like peak behaviour which indicates the presence of mixed spinel structure. The saturation magnetization, coercivity and remanence increase with increasing sintering temperature from 250 to 550 degrees C. The non-saturation and low values of magnetization at high fields indicate the strong surface effects to magnetization in NiFe2O4 nanoparticles. The g-value calculated from electron spin resonance spectrum indicates the transfer of divalent metallic ion from octahedral to tetrahedral site (i.e. mixed spinel structure). The dielectric permittivity, loss tangent and ac conductivity measurements show strong temperature dependence at all frequencies. The observed ac conductivity response suggests that the conduction in ferrite nanoparticles is due to feeble polaron hopping between Fe3+/Fe2+ ions. Room temperature UV vis diffuse spectra indicate that NiFe2O4 is an indirect band gap material with band gap ranges from 1.27 to 1.47 eV with varying sintering temperature. The photoluminescence study clearly indicates that the. Ni2+ ions occupy both octahedral and tetrahedral sites confirming mixed spinel structure