Extended Data Fig. 4: Transient absorption (TA) measurements of carrier multiplication (CM) in undoped and Mn-doped PbSe/CdSe QDs.
From: Spin-exchange carrier multiplication in manganese-doped colloidal quantum dots
Pump-fluence-dependent femtosecond TA measurements of band-edge bleach dynamics in Mn-doped (sample Mn-1; a, c, d, f) and undoped (sample Un; b, c, e, f) PbSe/CdSe QDs probed at hvprobe = 0.84 eV (ΔA is the pump-induced change in sample absorbance). The measured transients are normalized so as to match the long-time tails. These measurements were conducted using pump photon energies hvp = 1.2 eV (a–c) and 2.41 eV (d–f), which corresponded to excitation below and above the CM threshold, respectively. In both cases, TA dynamics develop a fast Auger decay component at higher pump levels, which is consistent with generation of multiexcitons. However, only for the 2.41-eV excitation, the fast Auger component persists in the limit of sub-single-exciton pump levels, which is a signature of CM. In the case of hvp = 1.2 eV, for both doped and undoped samples (c; red and black symbols respectively), the exciton multiplicity (〈NX〉) derived from the analysis of the early- and late-time TA amplitudes tends to 1 in the limit of low pump fluences, indicating no CM. However, the same analysis for the case of hvp = 2.41 eV indicates 〈NX〉 of 1.23 and 1.5 for the undoped (f; black squares) and doped (f; red circles) samples, respectively. This is a signature of CM. The biexciton yield in the Mn-doped sample (ηXX = 50%) is more than twice as large as in the undoped sample (ηXX = 23%). Dashed lines in ‘c’ and ‘f’ are linear fits to the data.
