What is the explanation for sonoluminescence?

Answer 1

In case of sonoluminescence, you have ultrasonic sound sent to the air bubble in liquid. As liquid is very good conductor of sound, it goes to air bubble easily. Then the sound encounters the air in the bubble. Air is not good conductor of sound as compared to liquid. So the high energy ultrasound gives energy to the air molecules. Which gets ionized and get converted into oxides or ionized. The remaining 1 % of the Nobel gases can not be oxidized. As they have complete octet in there last orbit. So high energy is delivered to Nobel gases. You can have better effect of sonoluminescence in artificial bubbles with Nobel gas. They loose electron from there outer orbit. The ionized atoms repel each other due to positive charge. So the size of the bubble increases. (As Nobel gases have highest energy of ionization, they can emit highest energy.) Then as energy is released in 'quanta' in the form of light. (Here energy is released in the form of electromagnetic waves. But you can 'see' light only.) As energy is released from the atoms of Nobel gases, electrons re-enter there outer orbit. As a result of this re-entry of electrons, positive charge on the atoms of Nobel gases disappears. They no longer repel each other and the bubble shrinks back. This process can be repeated any number of times. This is purely physical phenomena, probably explained.