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.