Light emitted from a liquid that flows in a narrow channel as triboluminescence

The flow of a liquid through a narrow channel under a high pressure (on the order of tens of atmospheres) can be accompanied by emission of light, which has been termed hydroluminescence. We have shown that this light emission takes place both from the gas and from the liquid phase, with each type of emission being characterized by its own radiation spectrum. The spectra of hydroluminescence are similar to the spectra of photoluminescence obtained upon UV irradiation of a liquid under study. Therefore, the hydroluminescence of a liquid is not a light emission of a specific type; the flow through the narrow channel is only one of the ways of excitation of the light emission, which, in this case, is caused by friction. In other words, hydrodynamic luminescence can be referred to a wider class of phenomena—triboluminescence.