Titanosilicates with Strong Phase-Matched Second Harmonic Generation Responses

The
search for new and efficient nonlinear optical (NLO) materials
has been an active research because of their technological importance
in laser applications. Although a large number of frequency-doubling
oxides, phosphates, borates, and fluoride-containing borates were
found, no transition-metal silicate with useful NLO properties has
been reported. We have now synthesized and grown crystals of two new
titanosilicates, Li2K4[(TiO)­Si4O12] and Li2Rb4[(TiO)­Si4O12], by using a flux and supercritical hydrothermal method.
Their unique 3D framework structures contain highly compressed TiO5 square pyramids which are arranged one over the other to
form infinite ···Ti–O···Ti–O
straight chains with alternating short and long Ti–O distances.
These two materials meet the requirements for efficient second harmonic
generation including lack of center of inversion symmetry, large susceptibility,
phase matching, transmitting at wavelengths of interest, resistant
to laser damage, and thermally stable. These attributes make them
very attractive for frequency-doubling materials.