Figure 5. Multiexciton emission in RIRs.

(a) Fluence-dependent PL spectra of RIR sample III. At high fluence, a 140 meV blue shift of the emission is observed. (b) The PL intensity increases linearly with fluence up to 10 μJ cm⁻², suggesting strongly suppressed Auger recombination. (c) Streak camera image at a fluence of 11.2 μJ cm⁻², confirming the blue-shifted MX emission. The emission at 45 ns is shown for comparison; however, it does not yet correspond to the pure single-exciton PL, which should peak at 1.75 eV. (d) The spectrally integrated decay is multiexpontential, with lifetimes of 1.9 and 20 ns, respectively. Note that MX emission can already be discerned below 1 μJ cm⁻², while the linear increase of the PL persists up to 10 μJ cm⁻² (see b). (e) Sketch of the main electronic configurations of exciton, biexciton and triexciton ground states. The occupation of higher lying orbitals, whose piezoelectric confinement is weaker, enables stronger electron–hole overlap for bi- and triexcitons. (f) Electron and hole wavefunctions for the three lowest electron and hole orbitals in RIR sample III, showing an increasing shift towards the core centre.