Alain Ibanez

In situ diagnostics of the crystalline nature of single organic nanocrystals by nonlinear microscopy.

We elucidate the crystalline nature and the three-dimensional orientation of isolated organic nanocrystals embedded in a sol-gel matrix, using a polarized nonlinear microscopy technique that combines two-photon fluorescence and second harmonic generation. This technique allows the distinction between monocrystalline structures and nanoscale polycrystalline aggregates responsible for incoherent second harmonic signals.

Polymorphism and luminescence properties of CMONS organic crystals: bulk crystals and nanocrystals confined in gel-glasses

In order to compare the polymorphism of 1-cyano-1-(4-nitrophenyl)-2-(4-methoxyphenyl)ethene CMONS crystallized in solutions to that of CMONS nanocrystals grown in the pores of dense sol-gel matrices, we have first studied the CMONS polymorphism in various solvents which were then used in the nanocrystallization processes. The different polymorphs were characterized by differential scanning calorimetry, X-ray diffraction and absorption as well as luminescence spectroscopies. The differences observed between CMONS powders and CMONS nanocrystals illustrate the role played by the silicate matrices on the polymorphism of CMONS. This matrix effect would be used to stabilize a particular polymorph of an organic phase and thus to adjust the optical properties of the nanocomposite hybrid organic–inorganic material. uf6d9 2001 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Structural, dielectric, and optical properties of yttrium calcium borate glasses

Structural and optical properties of stable glasses in the Y2O3–CaO–B2O3 system, containing the same Y/Ca ratio as the YCa4O(BO3)3 (YCOB) crystal, were determined from Raman and reflectance infrared spectroscopy. Changes in optical functions with composition are associated with an increase in the number of non-bridging oxygen and to calcium/yttrium oxides content. Refractive indexes values (from 1.597 to 1.627 at λ=2u2002μm) are in good agreement with those of the YCOB crystal, an indication that these glasses are potential candidates for optical applications due to their ease of shaping as large bulk samples or fibers.

Crystal growth of hybrid nonlinear optical materials: 2-amino-5-nitropyridinium dihydrogenphosphate and dihydrogenarsenate

Abstract The 2-amino-5-nitropyridinium dihydrogenphosphate and dihydrogenarsenate crystals (2A5NPDP and 2A5NPDAs) are promising hybrid (organic-inorganic) materials for nonlinear optical devices. Their synthesis and crystal growth conditions from solution were optimized in order to obtain high quality and large crystals for optical studies. The crystal morphology is dependent of the solvent nature (H3XO4 with X = P, As or CH3COOH acidic solutions), supersaturation, crystalline quality and purity grade (tapering mechanism). The X-ray diffraction topography technique (Langs method) show a significant evolution of the defect nature and of the crystalline quality following the growth method and the purity grade.

Characterization of germanium surrounding in GeS, GeS2Ag2S and GeS2Ag2SAgI glassy systems by Ge K-edge X-ray absorption study

Abstract Extended X-ray absorption fine structure (EXAFS) measurements at the Ge K-edge were carried out at room temperature to determine the local structure of GeSx (1.5⩽x⩽2.33) binary glasses, (1−y)GeS2+yAg2S and (1−z) [GeS2+Ag2S]+zAgI glassy compositions. In all these chalcogenide glasses the local surrounding remains tetrahedral with a Geue5f8S and Geue5f8Ge (2.52 A) bonds. On the other hand, for S-rich binary compositions, Ge first shell is formed by four sulfur atoms. Thus, (g)GeS2 structure is composed of very slightly distorted GeS4 tetrahedra in agreement with the molecular cluster network and with the chemically ordered model. When Ag2S is added to the GeS2 glass former, a distortion increase of GeS4 units is noted, characterizing the typical network modifier role played by the silver sulfide. This effect is amplified by the addition of AgI doping salt for quaternary glasses.

Sur les chalcogeno-iodures d'antimoine SbXI(X =S, Se, Te): Structures et spectroscopie Mo¨ssbauer de121Sb

The crystal structure of SbXI(X =Se, Te) compounds has been determined by means of three-dimensional intensity data. The crystal structure of SbSeI, orthorhombic, space groupPnma witha = 8.698(2), b = 4.127(1), c = 10.412(2) A, was refined at several temperatures (180 K,R = 0.021; 293 K,R = 0.020; 320 K,R = 0.023) in correlation with the paraelectric structure or SbSI stable above 293 K. The crystal structure of SbTeI, triclinic, space groupP1¯, witha = 7.570(3), b = 7.159(3), c = 4.228(3) A, α = 107.22(5), β = 106.18(4), γ = 77.19(3)° has been determined by symbolic addition method and refined to a finalR value of 0.035. These structures are built up from infinite weakly linked ribbons (SbX2)n of trigonal SbX3 with SbX bonds of 2.605(1), 2.795(1)A(X =Se), and 2.829(1), 2.953(1), 2.955(1)A(X =Te). The nature of SbX and SbI bonds is discussed in terms of the S, Se, Te substitution. Antimony-121 Mo¨ssbauer spectra have been recorded at liquid helium temperature. The data are discussed with regard to the stereochimical activity of the antimony (III) lone pair of electrons. For SbTeI the Mo¨ssbauer parameters are interpreted in terms of direct population of conductance bands by nonbonding electron pairs.

Crystal growth of a stable nonlinear optical organic material: 2-amino-5-nitropyridinium monohydrogen L-tartrate

We report on the optimization of synthesis, solubility and crystal growth from solution of 2-amino-5-nitropyridinium l-tartrate (labelled 2A5NPLT). This newly engineered guest-host hydrogen-bonding salt exhibits a quasi-perfect polar alignment of the nonlinear chromophores in the crystalline lattice which is promising for optimized Pockels electrooptic properties. In addition, the dense and 3D-intermolecular framework built up by short hydrogen bonds leads to improved thermal, mechanical and chemical stability compared with that of organic molecular crystals. The solvent selection allowed the elaboration of bulky crystal by the temperature lowering method. Synchrotron X-ray diffraction topography experiments carried out on uncut crystals revealed a high crystalline perfection.

Luminescent and thermo-optical properties of Nd3+-doped yttrium aluminoborate laser glasses

In this work we performed a thorough spectroscopic and thermo-optical investigation of yttrium aluminoborate glasses doped with neodymium ions. A set of samples, prepared by the conventional melt-quenching technique and with Nd2O3 concentrations varying from 0.1 to 0.75u2002molu2009%, were characterized by ground state absorption, photoluminescence, excited state lifetime measurements, and thermal lens technique. For the neodymium emission at 1064 nm (F43/2→I411/2 transition), no significant luminescence concentration quenching was observed and the experimental lifetime values ranged around 70u2002μs. The obtained values of thermal conductivity and diffusivity of approximately 10.3×10−3u2002W/cmu2009K and 4.0×10−3u2002cm2/s, respectively, are comparable to those of commercial laser glasses. Moreover, the fluorescence quantum efficiency of the glasses, calculated using the Judd–Ofelt formalism and luminescence decay, lies in the range from 0.28 to 0.32, larger than the typical values obtained for Nd3+ doped YAl3(BO3)4 crystals.

New core–shell hybrid nanoparticles for biophotonics: fluorescent organic nanocrystals confined in organosilicate spheres

We have developed a versatile, one-step process to synthesize in large amounts hybrid core–shell nanoparticles (NPs) made up of an organic crystallized core embedded in amorphous organosilicate shells. These NPs exhibit a hydrophilic surface and a high fluorescence intensity arising from the organic crystal core. Their preparation is based on a controlled drying process of micrometre-sized droplets (spray) from sol–gel solutions leading simultaneously to the confined nucleation and growth of dye nanocrystals and to the formation of silica-based shells. In this paper, we present several experimental optimizations of the spray-drying process to reduce the average NP size and size distribution. This was achieved by combining several physical parameters of spray-drying and the chemistry of the initial sols. Original precursors were developed for the formation of optimized silicate shells. TEM analysis in diffraction mode showed that organic cores are single crystals. On the other hand, the negatively charged silicate shells led to colloidally stable NPs which is promising for the development of bright fluorescent tracers excited by two-photon absorption for in vivo imaging.

Thermo-optical characteristics and concentration quenching effects in Nd3+ doped yttrium calcium borate glasses.

In this work we present a comprehensive study of the spectroscopic and thermo-optical properties of a set of samples with composition xNd(2)O(3)-(5-x)Y(2)O(3-)40CaO-55B(2)O(3) (0 ≤ x ≤ 1.0 mol%). Their fluorescence quantum efficiency (η) values were determined using the thermal lens technique and the dependence on the ionic concentration was analyzed in terms of energy transfer processes, based on the Förster-Dexter model of multipolar ion-ion interactions. A maximum η = 0.54 was found to be substantially higher than for yttrium aluminoborate crystals and glasses with comparable Nd(3+) content. As for the thermo-optical properties of yttrium calcium borate, they are comparable to other well-known laser glasses. The obtained energy transfer microparameters and the weak dependence of η on the Nd(3+) concentration with a high optimum Nd(3+) concentration put this system as a strong candidate for photonics applications.