We used commercially available (001) single crystals of
LiTaO3, LiNbO3, KTaO3, SrTiO3, and BaTiO3. All samples were
0.5 mm thick. The samples were irradiated by Arþ-ion beam for
30 min (acceleration voltage: 300 V and Ar gas flow: 3 ml min1
).The PL measurements were performed with a monochromator
connected to a charge-coupled device camera. Two types of light
source were used for photoexcitation: cw laser (He-Cd laser,
3.82 eV) and wavelength-tunable pulse laser. The excitation
pulses were obtained from an optical parametric amplifier system
based on a regenerative amplified mode-locked Ti:sapphire laser
with a pulse duration of 150 fs and a repetition rate of 1 kHz.