Computation and analysis of the characteristic spectra of Eu(II) ions in single-bubble sonoluminescence

Abstract Single-bubble sonoluminescence (SBSL) occurs when a tiny bubble with an extremely small volume, isolated within a liquid, periodically compresses and expands in response to a strong ultrasonic field, emitting a brief burst of bright light. Sonoluminescence spectroscopy serves as a powerful tool for analyzing the material structure and physical state of these bubbles. Recent experimental results have demonstrated that the sonoluminescence spectra of moving single bubbles exhibit the characteristic spectra of divalent europium ions [Eu(II)] in solutions containing europium chloride (EuCl 2 ). To elucidate the radiation mechanism of the characteristic spectra of Eu(II) ions during sonoluminescence, we combined fluid mechanics, the Keller–Miksis (KM) equation, and spectral equations to calculate the spectral intensity and radiation power of SBSL in EuCl 2 solutions, as well as the spatial distributions of temperature, pressure, particle number density, ionization energy, ionization degree and opacity within bubbles. The results indicate that the characteristic spectra of Eu(II) ions may arise from the transition radiation excited under a localized environment of high temperature, pressure, and density within bubbles. These findings could enhance our understanding of the mechanisms underlying sonoluminescence and potentially aid in the development of advanced diagnostic tools for analyzing high-energy processes in fluids.