Figure 4: Scheme of the proposed energy levels and the optical transitions.

(a) PL. (b) EL. In the EL scheme, the neutral ground-state dimer is stabilized by the injection of a charge (for example, a hole h+). Recombination with the opposite charge (an electron e−) leads to the population of a neutral dimer excited state in a configuration corresponding initially to the mixed dimer ground state before recombination.