Non-linear light emission of inorganic protonic diodes, H+LEDs†
Protons behave like electrons. This similarity leads to the concept of proton semiconductors, where water is treated as an intrinsic semiconductor. Water doped with acid becomes a protonic analog of an n-type semiconductor (with excess protons), while water doped with a base is an analog of a p-type semiconductor (excess of hydroxyl groups, “holes”). By combining these two materials, it is possible to create a proton p–n junction and finally even a light-emitting diode (H+LED) in which protons are the main charge carriers. This was first observed in our laboratory using a polymer stabilized device. The remaining problem to be investigated was the role of the electron current and the possible effect of polymer instability on light emission. Here we describe a device in which the mechanical stability is maintained by the use of (wet) SiO2 silica gel doped on one side with H2SO4 (proton donor) and SiO2 doped with Na2SiO3 (sodium silicate, water glass) on the other (proton acceptor)) or wet SiO2 (proton donor) and Al2O3 aluminum oxide (proton acceptor). All materials used are insulating to the flow of electrons and thermally stable. In the case of inorganic diodes H+LED, emission is extremely intense with non-linear optical effects – collimated light beams and forced Raman scattering (SRS), and the spectrum is blue shifted compared to the emission of polymer-stabilized diodes.