Mixed oxide xerogels based on titania or silica with non-linear optical properties

Kurzfassung

Much effort has been devoted to the development of materials, which exhibit nonlinear optical properties [1]. Nonlinear optical properties, especially frequency doubling, are only observed in materials with a non-centrosymmetrical crystal structure, like LiTaO3, LiNbO3 and KNbO3. The second harmonic generation effect of single crystals is well studied [2]. Lithiumtantalate is an interesting material for optical devices, because of the large electro-optic and nonlinear coefficients. Most studies are concentrated on the growth and properties of LiTaO3 single crystals, but the second harmonic generation effect of pure LiTaO3-xerogels and mixed SiO2-TiO2-LiTaO3-xerogels has not been investigated so far. We demonstrate the second harmonic generation effect on mixed oxide xerogels. SiO2- and TiO2-xerogel materials are prepared by the sol-gel process from two steps. The first step is the hydrolysis of tetra-ethylorthosilicate (TEOS) or tetra-n-butylorthotitanate (TBOT) with water, alcohol and a catalyst for pure titanium dioxide or silica dioxide xerogels [3,4]. The second step is heat treatment after gelation and ambient drying. Lithiumtantalate xerogels are synthesized by dissolving lithium ethoxide (LiEO) and tantalum ethoxide (TaEO) in ethanol under acidic conditions [5]. Mixed oxide xerogels from silica, titania and lithium-/ tantalum-ethoxide are prepared from TEOS, TBOT, LiEO and TaEO with different molar ratios. The mixed solution forms a gel after four hours. These wet gels are dried at 50°C for two days. Finally, the dried materials are heat treated at 500°C and 700°C. The as-prepared xerogel-materials exhibit frequency doubling (second harmonic generation, SHG), which was demonstrated with infrared light of 1064nm. [1] Xu, Y.: Ferroelectric materials and their applications. North-Holland, Amsterdam (1991) [2] Günter, P.: Nonlinear Optical Effects and Materials. Springer, Berlin (1999) [3] Hüsing, N., Schubert, U.:Aerogele - luftige Materialien: Chemie, Struktur und Eigenschaften. Angewandte Chemie Int. Ed. vol. 37, p. 23 (1998) [4] Pierre, A.C., Pajonk, G.M.: Chemistry of Aerogels and Their Applications. Chem. Rev. vol. 102, p. 4243 (2002) [5] Ono, S., Hirano, S.: Processing of highly oriented lithium tantalite films by chemical solution deposition. J. Mater. Res. vol. 10, p.2532 (2002)