Luminescence of Tb$^{3+}$ and Gd$^{3+}$ ions in sonolysis under the conditions of a single bubble moving in aqueous solutions of TbCl$_3$ and GdCl$_3$

Luminescence bands of Tb$^{3+}$ and Gd$^{3+}$ ions are detected during sonolysis in the regime of a moving single bubble in aqueous solutions of TbCl$_3$ and GdCl$_3$ salts with concentration 1–2 mol/L. Saturation with argon, low temperatures of solutions (-5$^\circ$C), and a high concentration of salts are the factors facilitating sonoluminescence of the metal. Comparison with the characteristics of sonoluminescence of lanthanide ions studied earlier in the regimes of multibubble and single-bubble sonolysis with a stationary bubble shows that the electron excitation of metal ions in the given case is associated with translational displacements of the bubble. Our results confirm the validity of the sonochemical model of microdroplet injection, which explains the penetration of nonvolatile salts into cavitation bubbles as a result of their deformation during intense movements.