Sonoluminescence is the initiation of bright flashes of light caused by imposing a loud, high frequency sound on a gas bubble contained within a liquid. According to one report  sound (typically 110 decibels at 25,000 Hertz) can cause a single air bubble in water to oscillate. As the pressure of the sound wave decreases (in the normal course of a single cycle of increasing and decreasing pressure), the bubble’s internal pressure causes it to increase in size to a maximum radius of about 70 micrometers. As the external pressure of the sound wave increases, the bubble begins to collapse. This collapse occurs partway through the rise in external pressure (and lasts about 15 x 10-6 seconds). The collapsing bubble walls shrink the bubble to less than a hundredth of its maximum size in about 15 microseconds. Then, as the bubble nears its minimum size, it emits a bright flash of light.
Attempts to find single bubble sonoluminescence in liquids other than water, were not successful. Pure nitrogen bubbles, for example, make hardly any light, a pure oxygen bubble was very dim, an 80-20 mixture of nitrogen and oxygen was a weak emitter, as well as the use of commercial liquid air (which has no argon!) Adding Argon boosted the light intensity (as did Helium and Xenon -- but each with a unique spectrum). A small gas impurity of about 1 percent seems to be one of the keys to sonoluminescence, despite the lack of simple explanation as to why this is an optimal amount.