Two-Photon Exciton Absorption in CdSe/CdS Nanoplatelets Colloidal Solution

This work devotes to investigation of two-photon absorption in a colloidal solution of nanoplatelets CdSe/CdS (3.5 and 2 monolayers of CdSe core and CdS shell respectively) in the case of light- and heavy-hole exciton excitation (1lh-1e, 536 nm) and (1hh-1e, 578 nm) by femtosecond laser radiation (1064 nm, 100 kHz). An open-aperture z-scan technique was utilized to measure nonlinear two-photon absorption coefficient which was found as β = 0.08 ± 0.01 cm/GW, two-photon absorption cross sections σ(2) ≈ 1.5 × 106 GM and nonlinear refraction index γ ≈ –5 × 10–16 cm2/W. The revealed features of the measured z-scan dependencies can be the evidence of amplified spontaneous emission in the colloidal solution of CdSe/CdS nanoplatelets at high intensity of two-photon excitation.