Three-photon absorption in water-soluble ZnS nanocrystals

TL;DR

This study demonstrates significant three-photon absorption in water-soluble ZnS nanocrystals, with potential applications in nonlinear optics and bioimaging, showing much higher 3PA cross-sections than similar nanocrystals and dyes.

Contribution

First measurement of large three-photon absorption cross-section in water-soluble ZnS nanocrystals using Z-scan and transient transmission techniques.

Findings

3PA cross-section ~2.7x10^-78 cm^6s^2photon^-2 at optimal wavelength

ZnS NCs exhibit nearly ten times larger 3PA than CdS NCs

3PA cross-section is 4-5 orders of magnitude higher than UV fluorescent dyes

Abstract

We report on large three-photon absorption (3PA) in glutathione-capped ZnS semiconductor nanocrystals (NCs), determined by both Z-scan and transient transmission techniques with 120-fs laser pulses. The monodispersed, water-soluble ZnS NCs are synthesized by a modified protocol with a mean diameter of 2.5 nm. Their 3PA cross-section is determined to be around 2.7x10^-78 cm^6s^2photon^-2 at an optimal wavelength of commercial Ti:sapphire femtosecond lasers. This value is nearly one order of magnitude greater than that of CdS NCs, and four to five orders of magnitude higher than those of the previously reported common UV fluorescent dyes.