Abstract
The propagation of ultrasound in a liquid media may lead to acoustic cavitation, which is the nucleation, growth, and rapid collapse of vapor-filled micro bubbles. The collapse of these bubbles is known to generate extreme conditions in the medium ("hot spots"), going with high temperatures and pressures, shock waves, chemical reactions, and possibly the emission of light, known as sonoluminescence (SL). Recent investigations considered the SL as a source of excitation for photoactive species contained in the sonicated media. For instance, Ashokkumar and Grieser studied the 515 kHz excitation of pyranine in aqueous solution; and showed that the observed emission spectra were resulting from SL excitation and not from chemical reactions that could occur in the sonicated media. This phenomenon, referred to as "sonophotoluminescence", was further observed during the sonication of fluorescent species in various aqueous and organic solutions. Later, these investigations led to the 20 kHz sonication of lanthanide salts in aqueous solutions. The Ln(III) excitation was suggested to occur via two mechanisms: (i) sonophotoluminescence, and (ii) collisional excitation of Ln(III) species at the bubble-solution interface with "hot" particles (radicals, excited molecules, etc.).