Computational investigation of Tb(III) ion line intensities in single-bubble sonoluminescence

We perform a computational fluid dynamics simulation of trivalent terbium [Tb(III)] ion line emissions from single-bubble sonoluminescence (SBSL). Our simulation includes dynamic boundary conditions as well as the effects of gas properties and quenching by species, such as nitrite ion (NO_{2}^{-}). Simulation results demonstrate that when the maximum temperature inside a dimly luminescing bubble is relatively low, emission peaks from excited Tb(III) ions are prominent within the emission spectra. As the maximum temperature of the bubble increases, emission peaks of Tb(III) ions fade away relative to the continuum background emission. These calculations match observations of Tb(III) line emissions from SBSL occurring in aqueous solutions of terbium nitrate [Tb(NO_{3})_{3}] under an argon gas atmosphere. The evolution of the radiation energy spectrum over time for sonoluminescing bubbles provides a clear mechanism explaining Tb(III) emission peaks gradually merging into the continuous background emission as the radiation power increases.