Water doped with H+ and HO− enables the formation of a protonic p–n junction, which works similarly to a typical, electron-based p–n junction, including light emission when electrically powered. Polymers provide mechanical stability.

Polyaniline doped with H2SO4 is used as an active material in the first polymer random laser directly electrically powered.

Protons behave like electrons. This similarity leads to a concept of protonic semiconductors, where water is treated as an intrinsic semiconductor. When doped with an acid, water becomes the protonic...

Tuning of the emission within the near-infrared to visible range is observed in p -toluenesulfonic acid-doped polyaniline light emitting diodes (PANI/PTSA), when water molecules are absorbed by the active material (wet PANI/PTSA). This is a hybrid material that combines a conjugated π-electron system and a proton system, both strongly interacting in close contact with each other. The proton system successfully competes with the electron system in excitation energy consumption (when electrically powered), thanks to the inductive resonance energy transfer from electrons to protons in wet PANI/PTSA at the energy levels of combination of vibrations and overtones in water, with subsequent light emission. Wet PANI/PTSA, in which electrons and protons can be excited parallelly owing to fast energy transfer, may emit light in different ranges (on a competitive basis). This results in intense light emission with a maximum at 750 nm (and the spectrum very similar to that of an excited protonic system in water), which is blue-shifted compared to the initial one at ∼850 nm that is generated by the PANI/PTSA dry sample, when electrically powered.