Ultrasonic vibrations of a single-piezoelectric crystal ofLiNbO3and CdS can excite luminescence of gas near the crystal surface. Light excitation starts at ultrasonic intensity above a certain threshold. This threshold lies in the range 3–10W/cm2and corresponds to the unpinning of dislocations and beginning of their reversible motion in the piezoelectric crystal. The effects constitute a new class of acousto-optic and dislocation phenomena having the main feature of energy transformation from ultrasound in solid to luminescence of gas at normal atmospheric pressure. The unpinning of dislocations is shown to be critical for sonoluminescence excitation. ©1997 American Institute of Physics.