When two gold nanoparticle spheres are pushed sufficiently close together, the gap between them acquires a red colour, as the gold’s electrons interact with white light.
When pushed even closer together - less than 0.35 nanometres apart - the electrons can switch from one particle to the other and produce a change in colour, from red to blue, in the space between the particles.
Physicists have observed this phenomenon - known as the quantum regime - for the first time, confirming electrons can change from one nanoparticle to another when they are close enough, to reduce accumulated charge.
Read more at Elhuyar Fundazioa