Hydrothermal single crystal growth and second harmonic generation of Li^sub 2^SiO^sub 3^, Li^sub 2^GeO^sub 3^ and Li^sub 2^Si^sub 2^O^sub 5

The growth of large high quality single crystals of three lithium silicates and germanates Li2SiO3, Li2SiO5, and Li2GeO3 is described. The crystals are all grown using hydrothermal fluids at 650 °C and 1 kbar using simple oxide feedstock and 3–6 M LiOH serving as both the lithium ion source and mineralizer. The crystals could be grown by spontaneous transport without any specific seeding, and grew between 2 and 10 mm/edge and without evidence of cracking, physical twinning or multiple domain structures. The crystals were characterized by single crystal diffraction, UV–vis spectroscopy and Raman spectroscopy. All the crystals are acentric and polar. Preliminary nonlinear optical properties were investigated using the Kurtz method and indicate that the crystals exhibit Type-1 phase matching ability, and Li2SiO3 demonstrates a significant nonlinear optical conversion efficiency, making it of potential interest as a UV NLO crystal.