Luminescence of aromatic hydrocarbon molecules in the sonication of terbium sulfate suspensions

The sonication of terbium sulfate suspensions in benzene, toluene, and p-xylene induces intense UV luminescence (260-320 nm). The luminescence bands coincide with the fluorescence spectra of these aromatic hydrocarbons, but it is not observed in their sonoluminescence spectra. Furthermore, the spectra of ultrasound-initiated luminescence of the suspensions defined as sonotriboluminescence, which is 10³ times more intense than the sonoluminescence of hydrocarbons, exhibit also emission from the ^∗Tb³⁺ ion. The luminescence of ^∗N₂, which is observed during traditional triboluminescence of terbium sulfate in air, is hardly detectable in the case of sonolysis of terbium sulfate suspensions in aromatic hydrocarbons, but can be observed on decreasing the temperature of the suspensions, which decreases the saturated vapor pressure of the liquids. A possible mechanism of excitation of aromatic hydrocarbon molecules during sonotriboluminescence is discussed.