Yvette Le Fur

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.  2001 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Engineering of non-linear optical crystals displaying a quasi perfect polar alignment of chromophores

Four non-linear optically active crystals based on organic salts obtained by bis-protonation of four diamines (trans-(±)-1,2-, trans-(1R,2R)-(–)-, cis-1,2-diaminocyclohexane or R-(–)-2-methylpiperazine) by 2-methoxy-4-nitrophenol have been prepared. Their crystal structures and non-linear optical efficiencies have been studied. The two adjacent proton acceptor sites in 1,2-diaminocyclohexanes play an important role in aligning the 2-methoxy-4-nitrophenolate chromophores in a quasi-perfect polar arrangement by anchoring through short hydrogen bonds. In the case of the methylpiperazinium derivative the symmetrical 1,4 location of proton acceptor sites directs the chromophores to near antiparallel alignment by forming short hydrogen bonds. The second harmonic generation efficiencies at 1.064 µm of Nd 3+ :YAG laser light are equivalent to that of POM (3-methyl-4-nitropyridine-1-oxide) for the three diammoniocyclohexane derivatives and equivalent to twice that of urea for the methylpiperazinium derivative.

Synthesis and crystal structure of a noncentrosymmetric form of potassium strontium monovanadate KSrVO4

Abstract Transparent single crystals of KSrVO 4 were grown at 1500°C by the direct melt and slow cooling technique. X-ray crystallography has shown that this compound crystallizes in the orthorhombic system with the space group P 2 1 2 1 2 1 (No. 9). The lattice parameters are a = 5.865, b = 7.491, c = 10.021 A, and Z = 4. The structure is isotypical with β-K 2 SO 4 , but with a different space group. It can be regarded as made of independent [VO 4 ] 3− tetrahedra arranged in such way as to delimit large cavities where Sr 2+ and K + are located in eight- and ninefold coordination spheres, respectively. The mean interatomic distances K–O, Sr–O, and V–O are equal to 2.952, 2.645, and 1.720 A, respectively.