Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.

Figure 18 Schematic of transitions illustrating two possible decay channels for abiexciton composed of two ground-state excitons interacting with the energy dE 2 .These two channels (denoted as tx bx,0 and tx bx,1 ) produce an exciton occupyingeither the lowest manifold of ‘‘emitting’’ states (denoted as EM) or a higher-lyingmanifold of ‘‘absorbing’’ states (denoted as ABS); exciton energies for these twomanifolds are E 1 x and E1 x , respectively.after a rapid Auger decay of states with N z 3. We used this model in order todescribe pump-dependent TA/gain signals in Fig. 17 (solid line). The best fitto the experimental data was obtained for a biexciton shift of 0.4G, where Gwas the width of the emitting transition (a full width measured at a halfmaximum).In contrast to a purely state-filling model (dashed line), whichonly provides a reasonable fit at high excitation densities (hNi>2), the‘‘biexcitonic’’ model (solid line) describes well the experimental dataset acrossthe entire intensity range hNi=0.5–8.Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.