Size regulation by bandgap-controlled etching: Application to germanium nanoparticles

A germanium (Ge) nanoparticle surface was etched in an aqueous solution under monochromatic light irradiation in the infrared-to-ultraviolet region. Since the bandgap widened up to the photon energy of the irradiating light, the average size of the nanoparticles was controlled and the size distribution narrowed. The quantum size effect explained the correlation between the resulting bandgap energy and the final size. The etched nanoparticles showed blue-green or red-infrared photoluminescence (PL) after the surfaces were terminated with organic molecules or hydrogen atoms. The PL peak energy was independent of size, indicating PL was due to radiative recombination via localized states at the Ge core surface.