Luminescence of trivalent lanthanide ions excited by single-bubble and multibubble cavitations.

This article focuses on the possibility of exciting some lanthanides (Ce3+, Tb3+, Gd3+, and Eu3+) by ultrasound in aqueous solutions. Depending on the lanthanide ions and on the acoustic cavitation conditions (single-bubble or multibubble systems), the excitation mechanism is shown to be photoexcitation (e.g., for Ce3+) or collision-induced excitation (e.g., for Tb3+). The sonoluminescence of Tb3+ is studied in detail at various ultrasonic frequencies, allowing quantification of the amount of quenching. The latter is much stronger in sonoluminescence than in photoluminescence due to the particular properties of acoustic cavitation. Complexation with citrate ions enhances manifold sonoluminescence of lanthanides due to reduction of intra- and inner-molecular quenching.