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

Abstract

We study the second harmonic generation effect (SHG) in transparent, nanosized xerogels prepared by the sol-gel method. The pure silica and titiania xerogels are synthesized by hydrolysis of TEOS (tetra-ethylorthosilicate) and TBOT (tetra-butylorthotitanate) as precursors under acidic conditions, followed by gelation of the sols and a special method of ambient drying. Lithiumtantalate xerogels start with a sol based on lithiumethoxid (LiEO) and tantalumethoxide (TaEO) dissolved in ethanol with the addition of acetic acid. The material is prepared under protective atmosphere in a glove box. Mixed oxide xerogels from silica, titania and lithiumtantalate are prepared from TEOS, TBOT, LiEO and TaEO with various ratios of the oxides. The dried samples are heat treated at 500 or 700°C. We observed in these mixed oxide xerogels frequency doubling properties and the possibility to modify continuously the refractive index of the xerogels over a wide range from 1.2 to 2.1. The paper presents the preparation methods and discusses the optical properties.