Syntheses of nanocrystalline BaTiO₃ and their optical properties

Stoichiometric and titanium-excess nanocrystalline barium titanates were synthesized using a hydrothermal process at various hydrothermal temperatures and with further heat treatment at 500 °C and 900 °C. Owing to the different process conditions, the excess titanium exists in different states and configurations within the nanocrystalline BaTiO₃ matrix; this was demonstrated by X-ray diffraction, Raman scattering, and photoluminescence. In these nanocrystalline BaTiO₃, the 590, 571, 543 and 694 nm light emission bands were observed; mechanisms leading to such emissions were also discussed.