Why boost quantum dots with rare-earth ions?

Rare earth ions are known to exhibit visible luminescence lines whose energy, intensity and half-value width depend little on the matrix. This remarkable property, due to the nature of the energetic transitions involving deep-layer electrons "protected" from the influence of the matrix by the screening caused by outer-layer electrons, can be used to produce light-emitting devices. Implantation or chemical doping of bulk semiconductors with rare-earth ions is being investigated in this context, but has one notable drawback: because the carriers (electrons and holes) are able to circulate freely in the material, the probability of non-radiative recombination is high compared with the probability of radiative recombination and concomitant excitation of the rare-earth ion levels. As a result, light emission efficiency is low, all the more so when the temperature is high and the thermally-activated...