Reversible nanoparticle gels with colour switching

Assembly of semiconductor nanoparticles into gel structures and their subsequent behaviour is one of the less-developed areas in nanochemistry. We demonstrate here a simple luminescent gel from CdTe nanoparticles in aqueous solution. Its structure can be described as an infinite network from chainlike branched structures. The recrystallization into the solid monocrystalline nanowires is prevented by increasing content of sulphur in the nanoparticles, which drastically increases the recrystallization energy. Brief sonication returns the system into the sol state. This switching behaviour is reversible and is accompanied by equally reversible emission colour switching. Such properties are much needed in a variety of media-responsive (i.e. “smart”) optoelectronic materials. This system will also be useful as a convenient research tool for the observation of dynamics of aqueous nanoscale colloids.