Laser-Induced Fluorescence of Wet Porous Silicon as Laser-Induced Fluorescence of H3O+

Abstract

Typically, the production of porous silicon is an electrochemical etching of monocrystalline silicon wafers, which are connected to the anode, in ethanol-aqueous HF solutions. In the process of etching, it turns out porous silicon, which is saturated with water, which is rich in protonated molecules H 3 O + , formed as a result of a number of well-known physicochemical processes. At the same time, the presence of molecules of such protonated water in the composition of freshly prepared porous silicon is usually ignored. At the same time, both the ability of protonated water to fluoresce under the action of laser radiation in the UV range, and the possible contribution of such fluorescence to the total fluorescence of porous silicon induced by a UV laser is ignored. Since such ignoring seems to be incorrect, the possible contribution of laser fluorescence of water enriched with its protonated molecules to the laser fluorescence of moistened porous silicon is discussed here. Since this may be important for the correct interpretation of the results obtained when studying the spectra of laser-induced fluorescence of porous silicon moistened with aqueous solutions, in particular – with aqueous solutions of biological substances, the unique properties of such water are also demonstrated. Thus, the exceptional penetrating ability of positively charged water is visualized, due to which it is able to transfer from the hydrated shells of biopolymers to porous silicon and enhance its laser-induced fluorescence. It also demonstrates the exceptional ability of positively charged water to evaporate; which makes it possible to explain the rapid disappearance of the fluorescence of porous silicon, which is observed during its drying.