I have heard that if you collapse a bubble in the water with some sort of sound wave it will produce light. Is it a special gas or just a bubble of air?And is it a special wave sound?
I wonder what the reason behind this phenomenon could be?
Although there are some ah, interesting hypotheses... (https://en.wikipedia.org/wiki/Sonoluminescence)
... addressing the light emission, the general consensus seems to be that it's plain ol' gas compression arising from the infalling spherical wall of water. Before the gas has chance to be absorbed, it is heated to the point of incandescence.
And such an amazing thing can be readily replicated with very modest equipment. A variety of gases dissolved in water have been shown to behave in this way. As have a variety of non-aqueous liquids.
The light emission means that electronic excitations have occurred. How to produce these excitations: with ionizing radiation or by means of strains. Without radiation, there must be a source of strains. When the strains rates are high there are interactions between the deformation waves and the electrons, particularly in the vicinity of the defects where there is energy localization. How to produce stains and high strain rates? By shocks or annihilation of defects. Is this known? Yes! Since defects are internal to the materials, energy is stored there and this energy is the main cause of aging and material damage. When subjecting a material (insulator) to impact, large variations in polarization, conductivity, and temperature are produced to cause the formation of hot spots. These phenomena can also be observed in the vicinity of defects (dislocations) which move or annihilate. This reasoning is classic in detonics but not in electrical engineering or mechanics. For more information, see the Coffey or Blaise and Le Gressus publications (https://aip.scitation.org/doi/10.1063/1.5047673). You will thus go to the heart of the phenomena of explosion, breakdown and fracture, So a neophite who asks a good question progresses faster than specialists who do not think about it!