Abstract
Spectrally resolved nonlinear optical properties of colloidal InP@ZnS core-shell quantum dots of various sizes were investigated with the Z-scan technique and two-photon fluorescence excitation method using a femtosecond laser system tunable in the range from 750 nm to 1600 nm. In principle, both techniques should provide comparable results and can be interchangeably used for determination of the nonlinear optical absorption parameters, finding maximal values of the cross sections and optimizing them. We have observed slight differences between the two-photon absorption cross sections measured by the two techniques and attributed them to the presence of non-radiative paths of absorption or relaxation. The most significant value of two-photon absorption cross section σ2 for 4.3 nm size InP@ZnS quantum dot was equal to 2200 GM, while the two-photon excitation action cross section σ2Φ was found to be 682 GM at 880 nm. The properties of these cadmium-free colloidal quantum dots can be potentially useful for nonlinear bioimaging.
Highlights
Resolved nonlinear optical properties of colloidal Indium phosphide (InP)@ZnS core-shell quantum dots of various sizes were investigated with the Z-scan technique and twophoton fluorescence excitation method using a femtosecond laser system tunable in the range from 750 nm to 1600 nm
The development of advanced biophotonic techniques utilizing the phenomenon of two-photon absorption (TPA), such as nonlinear fluorescence microscopy or two-photon photodynamic therapy, requires new materials with well characterized optical properties, high TPA cross sections, and efficient two-photon excited emission (TPEE)
Measurements of TPA cross sections of various quantum dots (QDs) are often performed for a single wavelength only that does not necessarily correspond to the maximum of the TPA band, and the reports lack the confrontation of the obtained values with the quantum yield (QY) of the TPEE, which is a crucial parameter in microscopy imaging applications
Summary
Resolved nonlinear optical properties of colloidal InP@ZnS core-shell quantum dots of various sizes were investigated with the Z-scan technique and twophoton fluorescence excitation method using a femtosecond laser system tunable in the range from 750 nm to 1600 nm. Optical nonlinearities of colloidal InP@ZnS core-shell quantum dots probed by Z-scan and two-photon excited emission
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