New materials for nonlinear optical applications : the nonlinear refractive index of colloidal PbSe quantum dots

We present a detailed study of the nonlinear optical properties of colloidal PbSe quantum dot (Q-PbSe) suspensions and thin films. The nonlinear refractive index n2 has been measured with the Z-scan technique as a function of wavelength (1.20 -- 1.75 textmum), optical intensity and nanocrystal volume fraction. The n2-spectra show negative resonances near the Q-PbSe optical transitions. We attributed the high n2 to biexciton creation within the Q-PbSe. The n2 of a close-packed thin Q-PbSe film is 6 orders of magnitude larger than values for bulk Si of GaAs at telecom wavelengths, suggesting that Q-PbSe might be a promising material for all optical signal processing.info:eu-repo/semantics/publishe

Size-dependent optical properties of colloidal PbS quantum dots

We quantitatively investigate the size-dependent optical properties of colloidal PbS nanocrystals or quantum dots (Qdots) by combining-the Qdot absorbance spectra with detailed elemental analysis of the Qdot suspensions. At high energies, the molar extinction coefficient epsilon increases With the Not volume d(3) and agrees with theoretical calculations using the Maxwell-Garnett effective medium theory and bulk values for the Qdot dielectric function. This demonstrates that quantum confinement has no influence on E in this spectral range, and it provides an accurate method to calculate the Qdot concentration. Around the band gap, epsilon only increases with d(1.3), and values are comparable to the epsilon of PbSe Qdots. The data are related to the oscillator strength f(if) of the band gap transition and results agree well with theoretical tight-binding calculations, predicting a linear dependence of f(if) on d. For both PbS and PbSe Qdots, the exciton lifetime tau is calculated from f(if). We find values ranging between 1 and 3 mu s, in agreement with experimental literature data from time-resolved luminescence spectroscopy. Our results provide a thorough general framework to calculate and understand the optical properties of suspended colloidal quantum dots. Most importantly, it highlights the significance of the local field factor in these systems

Towards FAIR GNSS data: challenges and open problems

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Ultrafast phase modulation in CdSe colloidal quantum wells

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ORCID @ UGent

“ORCID @ UGent” was presented at the ORCID Belgium Workshop at the Royal Library of Belgium on March 13, 2018 by Dries Moreels (University of Ghent).<p></p