Inversion of the relative probabilities of the f--f and f--d transitions in the (Ln$^{3+}$) lanthanide ions at their radio- and sonoexcitation as compared to photoexcitation

The results of measuring the efficiencies of the formation of electronically excited states of the Ln³⁺ lanthanide ions in aqueous solutions in the processes of radioluminescence and multibubble sonoluminescence are analyzed. In both cases, electronic excitation occurs due to inelastic collisions of Ln³⁺ ions with (for radioluminescence) charged ionizing particles in liquid and (for multibubble sonoluminescence) high-energy particles, primarily electrons, in the gas phase of cavitation bubbles. In both processes, the efficiencies of exciting ions whose luminescence states appear in the 4f-5d transitions (Ce³⁺ and Pr³⁺) are significantly lower (by an order of magnitude or larger) than the efficiencies of exciting ions whose luminescence states appear in the 4f-4f transitions (Gd³⁺ and Tb³⁺). Therefore, the probability of the f-d transitions is lower than the probability of the f-f transitions in lanthanide ions excited by collisions with the charged particles and the relative probabilities of these transitions are inverted in these processes as compared to photoexcitation.