Spectral Research Of Single-bubble Sonoluminescence In The Rare-earth Salt Aqueous Solutions

A single bubble in liquid can be levitated by a standing ultrasound wave and pulsate periodically. The sound energy is highly concentrated and turns to light. This phenomenon is called single-bubble sonoluminescence (SBSL). SBSL has been one of the hot topics in acoustics and physics in recent decade, and is full of high research value. Spectroscopic study is always a major and effective experimental tool, especially for the investigation of line spectra which reflect the component of luminophor.This paper mainly studies the spectra of SBSL in the solutions with the addition of rare-earth elements and focuses on a series of OH radical’s line spectra from the transitions of vibrational levels with the change of the driving sound pressure. We obtain the parametric relation between line spectrum and the driving sound pressure.In the SBSL spectra of the terbium chloride aqueous solutions dissolved with the noble gas Ar, not only the characteristic spectra of Tb3+ion and Ar atom are observed but also a series of line spectra which is identified as emissions from the transitions of OH radical vibrational levels from the first excited state A2∑+to the ground state X2FI, including (0,0) transition at307nm,(0,1) transition at335nm and (1,0) transition at276nm. In the SBSL spectra of pure water dissolved with Ar Only the (0,0) line at307nm can be observed. So the rare-earth elements promote the generation of the line spectra at276nm and335nm in the SBSL spectra. Under the condition of fixed driving ultrasonic frequency and different sound pressures, the changes of the OH radical’s line spectra are observed. The experimental results show that higher sound pressure is conducive to the appearance of the line spectrum at276nm while lower sound pressure is favorable for the appearance of the line spectra at307nm and335nm. The relative intensity of the line spectrum in the total spectrum is expressed quantificationally by defining an intensity ratio of the line spectrum to the continuous spectrum. In addition, the effects of the driving sound pressure on the intensity ratios of different line spectra are given.The clear characteristic spectra of the rare-earth element Tb are firstly observed in our SBSL experiment. We correct the one-side view that lower sound pressure is favorable for the appearance of the line spectra. The observation of this experiment related to the sound pressure is explained systematically. This paper riches the data of the SBSL line spectra and is helpful for the understanding of the mechanism of the line spectra.