“…A weak contribution of the first excitonic resonance to the TPA spectrum in comparison to energies in the quasi-continuum, where strong TPA is observed, has been reported for CdSe QDs, 32,37 CdS NRs and QDs, 18 as well as for CdSe/CdS dots in rods. 40 For NPLs we see an extreme increase of two-photon absorption from two-photon energies resonant to the first excitonic transition to the continuum absorption region. The increase has a stepwise character because the nanoplatelets' step-like 2D density of states leads to three steps (for the HH, LH, and SO continua), shifted to higher energies with respect to the first HH, LH and SO exciton transitions by the exciton binding energies, estimated to the order of 200 meV.…”