pH-Induced transformation of ligated Au 25 to brighter Au 23 nanoclusters

Thiolate-protected gold nanoclusters have recently attracted considerable attention due to their size-dependent luminescence characterized by a long lifetime and large Stokes shift. However, the optimization of nanocluster properties such as the luminescence quantum yield is still a challenge. We report here the transformation of Au25Capt18 (Capt labels captopril) nanoclusters occurring at low pH and yielding a product with a much increased luminescence quantum yield which we have identified as Au23Capt17. We applied a simple method of treatment with HCl to accomplish this transformation and we characterized the absorption and emission of the newly created ligated nanoclusters as well as their morphology. Based on DFT calculations we show which Au nanocluster size transformations can lead to highly luminescent species such as Au23Capt17

Nonlinear absorption and nonlinear refraction: Maximizing the merit factors

Both nonlinear absorption and nonlinear refraction are effects that are potentially useful for a plethora of applications in photonics, nanophotonics and biophotonics. Despite substantial attention given to these phenomena by researchers studying the merits of disparate systems such as organic materials, hybrid materials, metal-containing molecules and nanostructures, it is virtually impossible to compare the results obtained on different materials when varying parameters of the light beams and different techniques are employed. We have attempted to address the problem by studying the properties of various systems in a systematic way, within a wide range of wavelengths, and including the regions of onephoton, two-photon and three-photon absorption. The objects of our studies have been typical nonlinear chromophores, such as π-conjugated molecules, oligomers and polymers, organometallics and coordination complexes containing transition metals, organometallic dendrimers, small metal-containing clusters, and nanoparticles of various kinds, including semiconductor quantum dots, plasmonic particles and rare-earth doped nanocrystals. We discuss herein procedures to quantify the nonlinear response of all of these systems, by defining and comparing the merit factors relevant for various applications

Nonlinear absorption spectra of ethidium and ethidium homodimer

The Z-scan technique was used to determine the spectral dependence of the nonlinear absorption in well-known DNA intercalators: ethidium bromide and its homodimer. It is found that the compounds show essentially the same features of their nonlinear absorption spectra with the magnitudes of the relevant cross sections scaling with molecular weight of chromophore compound

Correction: Interactions of Isophorone Derivatives with DNA: Spectroscopic Studies

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Shell-thickness-dependent nonlinear optical properties of colloidal gold nanoshells

International audienceThird-order nonlinear optical properties of gold nanoshells of different thickness were investigated over a broad wavelength range (530-1200 nm) by the Z-scan technique using femtosecond laser pulses. Nonlinear absorption of the nanoshells is dominated by strong absorption saturation phenomena. Thereciprocals of the relevant saturation intensities are the highest at the maxima of one-photon absorption(1 PA) bands for all the studied nanoshells but the scaling with the one-photon extinction coefficientswithin the relevant absorption bands is rather approximate. The reciprocals of the saturation intensitiesscaled by the values of the extinction coefficients are also found to decrease with the increase of theshell thickness. This can be attributed mostly to the increase of the contribution of the scattering of NIRlight to the total extinction of the solutions. The two-photon absorption (2 PA) behavior is found to bedominant only within the shortest wavelength range studied for the gold nanoshells with the thinnestshells which exhibit high 2 PA cross-section values, withs2reaching 5.1 X 1010G

Post-synthesis reshaping of gold nanorods using a femtosecond laser

International audienceThis work describes the interaction between femtosecond laser pulses (B130 fs, 800 nm) and gold nanorods (NRs) leading to reshaping of the NRs. We focus on the investigation of structural changes of the NRs and the parameters influencing the reshaping, like surface modification using sodium sulphide, laser power and the position of the longitudinal surface plasmon resonance band (l-SPR) with respect to the laser wavelength. A thermogravimetric analysis experiment is performed to examine changes in the composition of NRs upon heating. A new type of banana-shaped NPs is described and the conditions of their appearance are discussed