Line emissions from sonoluminescence in aqueous solutions of halide salts without noble gases

• Line emissions of Tb(III) ions were observed without the presence of noble gases.
• The halide ions help to generate a line emission during sonoluminescence.
• The intensity of a line emission mainly depends on the bubble's temperature.
• The definition of a line emission is related to the temperature of caviation bubble and the kind of host liquid.

Line emissions of trivalent terbium (Tb3+) ion were observed from single-bubble sonoluminescence (SL) in an aqueous solution of terbium chloride (TbCl3) that contained no noble gas. In addition, sodium (Na) lines were observed in multi-bubble SL in aqueous solutions of various halide salts that contained no noble gas. These observations show that the halide ions, such as Cl−, Br−, and I−, help for line emissions as the noble gases. The intensity of a line emission depends on both the chemical species produced by cavitation bubbles and the temperature of SL bubble that responds to the driving ultrasound pressure. With the increase of driving pressure, some line emissions attached to the continuous spectrum may become increasingly clear, while other line emissions gradually become indistinct.