E. de Matos Gomes

Crystal growth and characterization of a new nonlinear optical material: Urea L-Malic acid

A new nonlinear optical organic crystal, viz. Urea L-Malic acid, has been grown from aqueous solution employing the techniques of solvent evaporation and slow cooling. The grown crystals were found to be transparent in the visible region. The complete morphology of the crystal has been worked out and its hardness was evaluated using Vickers indentation method. The grown crystals were characterized employing several techniques such as micro-carbon-hydrogen-nitrogen analysis, X-ray diffraction, thermogravimetric analysis, differential thermal analysis, UV-VIS-IR spectroscopy and refractive index measurement. Preliminary measurements indicate that the second harmonic generation efficiency at a fundamental wavelength of 1064 nm is roughly three times that of KDP.

Novel charge transfer supramolecular assemblies with Keggin anions and 2-amino-5-nitropyridine

Several novel compounds with the non-linear optical chromophore 2-amino-5-nitropyridine (2A5NP) and Keggin polyoxoanions (alpha-isomers), having the general formula (2A5NP)(m)H(n)[XM12O40].xH2O, M = Mo, W, were synthesised. Compounds were obtained with X = P, n = 3, m = 3 and 4 and X = Si, n = m = 4 (x = 2-6). Thus, for each of the anions [PMo12O40]3- and [PW12O40]3- two different compounds were obtained, with the same anion and organic counterpart but with a different stoichiometric ratio. These presented different charge transfer properties and thermal stability. All compounds were characterised by spectroscopic and analytical techniques. The single crystal X-ray diffraction structure of (2A5NP)4H3[PMo12O40].2.5H2O.0.5C2H5OH showed that the water solvent molecules and the organic chromophores are assembled via infinite one-dimensional chains of hydrogen bonds with formation of open channels, which accommodate [PMo12O40]3- and ethanol solvent molecules.

Laser damage threshold studies on urea L-malic acid: A nonlinear optical crystal

A detailed study of surface laser damage performed on a nonlinear optical crystal, urea L-malic acid, using 7ns laser pulses at 10Hz repetition rate from a Q-switched Nd:YAG laser at wavelengths of 532 and 1064nm is reported. The single shot and multiple shot surface laser damage threshold values are determined to be 26.64±0.19 and 20.60±0.36GWcm−2 at 1064nm and 18.44±0.31 and 7.52±0.22GWcm−2 at 532nm laser radiation, respectively. The laser damage anisotropy is consistent with the Vickers mechanical hardness measurement performed along three crystallographic directions. The Knoop polar plot also reflects the damage morphology. Our investigation reveals a direct correlation between the laser damage profile and hardness anisotropy. Thermal breakdown of the crystal is identified as the possible mechanism of laser induced surface damage.

Piezoresponse force microscopy studies of the triglycine sulfate-based nanofibers

Local ferroelectric and piezoelectric properties of triglycine sulfate (TGS) nanocrystals embedded into poly(ethylene) oxide (PEO) electrospun fibers were examined by piezoresponse force microscopy (PFM). Piezoresponse contrast was found to be strongly dependent on the position being much stronger at the fiber periphery. A model of the distribution of TGS crystals inside the core-shell PEO-TGS fiber structure was proposed. TGS nanocrystals were unevenly distributed along the fiber axis and tend to grow near the surface of the fiber. The volume fraction distribution of the TGS crystals extracted from PFM measurements is in a good agreement with the data obtained from the dielectric constant measurements.

High nonlinear optical anisotropy of urea nanofibers

Nanofibers consisting of the optically nonlinear organic molecule urea embedded in both poly(ethylene oxide) (PEO) and poly(vinyl alcohol) (PVA) polymers were produced by the electrospinning technique. The second-harmonic generation produced by aligned fiber mats of these materials displays a strong dependence on the polarization of the incident light. In PVA-urea nanofibers the effectiveness in generating of the second-harmonic light is as high as that of a pure urea powder with an average grain size of 110 μm. The results suggest that single crystalline urea nanofibers were achieved with a long-range crystalline order extending into the range of 2–4 μm with PVA as the host polymer.

l-Tryptophan 4-nitro-phenol tris-olvate.

The title compound, C(11)H(12)N(2)O(2)·3C(6)H(5)NO(3), comprises a zwitterionic amino acid formed by two nearly planar groups: (i) the indole ring and Cβ, and (ii) the carboxyl group, Cα, as well as the amine N atom, with r.m.s. deviations of 0.0084 and 0.0038 Å, respectively. The angle between these idealized planes is 39.47 (9)°. The amine group of the amino acid is in a syn (-sc) arrangement relative to the ring system. The overall crystal structure results from the packing of sheets parallel to the (001) planes. These sheets are formed by a pair of screw axis related parallel networks bound by hydrogen-bond and π-π stacking interactions. The intermolecular cohesion of all organic residues in each of the latter two-dimensional networks is achieved via strong hydrogen bonding, nitro-π and π-π stacking interactions.

Ferroelectric properties of TGS crystals grown under an intense DC electric field

The application of electric field during crystal growth modifies the ferroelectric properties of triglycine sulphate (TGS) crystals. Scanning electron microscopic examination of freshly cleaved (0 1 0) surface shows the presence of some domains tilted with respect to the c-axis. It is suggested that the cause of the onset of domains misaligned with the c-axis is the partial pinning by the field of the rotation of the NH3 group of the glycine I molecule. The modified domains originate a decrease of the dielectric values, a reduced spontaneous polarization and an increase of the relaxation times. Crystals of TGS grown under field remain in a stable state with modified properties as long as they are not subjected to intense AC fields or annealed above the Curie temperature for more than two cycles. r 2002 Elsevier Science B.V. All rights reserved. PACS: 77.80.Dj; 77.84.� s; 77.84.Fa; 77.80.� e; 81.40.Rs

Antiferroelectric ADP doping in ferroelectric TGS crystals

Crystal growth, morphology, hysteresis and dielectric measurements on 20 mol% ammonium dihydrogen phosphate (ADP)-doped triglycine sulphate (TGS) crystals are reported. Crystals grew with morphology similar to phosphoric acid-doped TGS (TGSP). Inhomogeneous incorporation of dopants gives rise to a distribution in coercive fields in the different growth sectors. The incorporated dopant hinders polarization switching, which results in the increase in coercive field. No internal bias field is created by the dopant and the phase transition observed is similar to pure TGSP. The Curie point shifts to a lower temperature with increasing dopant concentration in the growth sectors. Significant changes in the activation energies of annealed specimen were identified.

Synthesis, structure, thermal and non-linear optical properties of L-argininium hydrogen selenite

L-Argininium hydrogen selenite (C(6)H(15)N(4)O(2)HSeO(3)) is a new semiorganic compound of the hydrogen selenite family with non-linear optical properties. The crystal lattice is monoclinic with unit-cell parameters a = 22.493 (5), b = 5.1624 (13), c = 9.730 (4) A, beta = 95.68 (3) degrees, V = 1124.3 (6) A(3), Z = 4, space group C2. Second-harmonic generation measurements performed on powder samples, using a Q-switched Nd:Yag laser (lambda = 1064 nm), showed the second-harmonic power to be about twice that of urea. Differential scanning calorimetry measurements revealed the existence of a phase transition with onset at 289 K.

Spectroscopic, nonlinear optical and quantum chemical studies on Pyrrolidinium p-Hydroxybenzoate – A phase matchable organic NLO crystal

Good quality and bulk single crystals of Pyrrolidinium p-Hydroxybenzoate (PYPHB), a newly identified nonlinear optical material, were grown for the first time. It crystallizes in monoclinic system with an acentric space group Cc. The molecular structure including carbon, proton positions and functional groups has been confirmed through nuclear magnetic resonance and Fourier transform infrared spectra. Its transmission window has been observed for UV-VIS-NIR region along with its theoretical limit. The photoluminescence behavior has been observed by exciting the crystal at 310 nm. The principal refractive indices and second order NLO coefficient of PYPHB are determined by Mach-Zehnder interferometer and Maker-Fringe experiments respectively. The coherence length and phase-matchablility of PYPHB crystals are measured to explore its efficacy towards device fabrications. The dipole moment, polarizability and molecular orbital energy of an isolated PYPHB molecule have also been calculated theoretically and the results are found to corroborate the experimental values.