Fig. 5
Exciton trapping paths. a Schematics 2D representation of an amorphous network (points connected by sticks) with a concentration of non-radiative defects (red diamonds) lower than the concentration of substituted sites characterized by large trapping cross section and high rate of radiative recombination (grey circles). Rs and Rd are the mean distances an exciton (at the centre) has to travel before finding substituted sites or defects, respectively. b Representation of an opposite situation of a network with large defectiveness and no site of preferential trapping and radiative decay. Rm represents the mean free path of exciton in the unperturbed network. In s-spr material, the calculated Rs and Rd values are about 5 and 9 nm, respectively, while Rm in SiO2 was estimated to range from 30 to 300 nm26. c Temperature dependence of the quantum yield ηrad at different ratios between radiative and non-radiative traps, in the case of trap density nsrad + ndeft = 0.1 mol%, Δε/kB = 70 K, and σtraps = 70σirad, with Δεsrad = Δεdef = Δε σsrad = σdef = σtraps
