Two-photon excited luminescence of sulfur quantum dots for heavy metal ion detection.

Spectrally-resolved third-order nonlinear optical properties of water-dispersed sulfur quantum dots (SQDs) were investigated in the wavelength range from 740 nm to 820 nm with the two-photon excited emission technique using a tunable femtosecond laser system. The maximum value of the two-photon absorption (TPA) cross-section () for ∼5.4 nm size SQDs was found to be 185 GM (Goeppert-Mayer unit), while the two-photon brightness ( × ) was found to be 1.

Third-Order Nonlinear Optical Properties of Aqueous Silver Sulfide Quantum Dots.

Wide spectral wavelength range (500-1600 nm) measurements of nonlinear optical properties of silver sulfide (AgS, with 2- or 3-mercaptopropionic acid, 2 or 3MPA ligands) quantum dots (QDs) in aqueous colloidal solutions were performed using the Z-scan technique with tunable ∼55 fs laser pulses at 1 kHz. We have identified regions of the occurrence of various NLO effects including two-photon absorption, nonlinear refraction, as well as saturation of one-photon absorption. At the same time, we evaluated the relationship between the properties of the QDs and the variation of the material that covers their surface.

Difluoroborate-based bichromophores: Symmetry relaxation and two-photon absorption.

Given potential applications of multiphoton absorbers, in the present work we have studied the symmetry-relaxation effects in one- and two-photon absorption spectra in two bichromophore systems based on difluoroborate core linked by biphenylene or bianthracene moieties. We have employed a palette of experimental methods (synthesis, one- and two-photon spectroscopy, X-ray crystallography) and state-of-the-art computational methods to shed light on how symmetry relaxation, a result of twisting of building blocks, affects one- and two-photon absorption of the two studied fluorescent dyes. Electronic-structure calculations revealed that the planarity of central biphenyl moiety, as well as deviations from planarity up to 30-40 deg.

QD:Puf Nanohybrids Are Compatible with Studies in Cells.

Colloidal semiconductor quantum dots (QD), as well as other nanoparticles, are useful in cell studies as fluorescent labels. They may also be used as more active components in various cellular assays, serving as sensors or effectors. However, not all QDs are biocompatible.

Multimodal polymer encapsulated CdSe/FeO nanoplatform with improved biocompatibility for two-photon and temperature stimulated bioapplications.

Multimodal polymer encapsulated CdSe/FeO nanoplatforms with dual optical and magnetic properties have been fabricated. We demonstrate that CdSe/FeO nanocapsules (NCs) upon excitation with UV radiation or NIR fs-laser excitation exhibit intense one- or two-photon emission at 535 nm, whereas the combination of an alternating magnetic field and 808 nm IR laser excitation results in heat generation. Since anticancer therapies require relatively high doses of FeO nanoparticles (NPs) to induce biologically relevant temperature jumps, the therapeutic effects of 0.

Silver nanowires as plasmonic compensators of luminescence quenching in single up-converting nanocrystals deposited on graphene.

Single nanocrystal spectroscopy is employed to demonstrate metal-enhanced optical response of Er/Yb doped up-conversion nanocrystals deposited on graphene upon coupling with silver nanowires. Direct interaction between nanocrystals and graphene results in quenching of up-conversion emission and shortening of luminescence decay times, due to the energy transfer to graphene. The amount of the energy absorbed by graphene can be enhanced by coupling Er/Yb doped up-conversion nanocrystals with silver nanowires.

Exploring Single-Nanoparticle Dynamics at High Temperature by Optical Tweezers.

The experimental determination of the velocity of a colloidal nanoparticle () has recently became a hot topic. The thermal dependence of is still left to be explored although it is a valuable source of information allowing, for instance, the discernment between ballistic and diffusive regimes. Optical tweezers (OTs) constitute a tool especially useful for the experimental determination of although they have only been capable of determining it at room temperature.

Nonlinear Optical Pigments. Two-Photon Absorption in Crosslinked Conjugated Polymers and Prospects for Remote Nonlinear Optical Thermometry.

Nonlinear optical (NLO) pigments are compounds insoluble in solvents that exhibit phenomena related to nonlinear optical susceptibilities (χ where n = 2,3,...

Controlling Two-Photon Action Cross Section by Changing a Single Heteroatom Position in Fluorescent Dyes.

The optimization of nonlinear optical properties for "real-life" applications remains a key challenge for both experimental and theoretical approaches. In particular, for two-photon processes, maximizing the two-photon action cross section (TPACS), the figure of merit for two-photon bioimaging spectroscopy, requires simultaneously controlling all its components. In the present Letter, a series of difluoroborates presenting various heterocyclic rings as an electron acceptor have been synthesized and their absorption, fluorescence, photoisomerization, and two-photon absorption features have been analyzed using both experimental and theoretical approaches.

The Two-Photon Absorption Cross-Section Studies of CsPbX (X = I, Br, Cl) Nanocrystals.

The CsPbX nanocrystals (NCs) with X = I, Br, Cl, or the mixture of Br:I and Br:Cl in a 1:1 ratio were synthesized and characterized by TEM, DLS, and XRD. Recrystallization of the small luminescent NCs in the metastable cubic phase into bigger orthorhombic nanocrystals was monitored by XRD and identified as the main cause of the nanocolloid coagulation. The recrystallization also leads to a decrease in the photoluminescence quantum yield (QY) of the colloidal solution and shortening of the emission lifetime.

Functional CdS-Au Nanocomposite for Efficient Photocatalytic, Photosensitizing, and Two-Photon Applications.

We demonstrate a low-temperature synthesis of hydrophilic, penicillamine-stabilized hybrid CdS-Au nanoparticles (NPs) utilizing different Au concentrations. The obtained hybrid nanomaterials exhibit photoluminescence quenching and emission lifetime reduction in comparison with their raw semiconductor CdS NPs counterparts. An increase of concentration of Au present at the surface of CdS leads to lower photoluminescence intensity and faster emission decays, suggesting more efficient charge separation when larger Au domains are present.

Exciton Binding Energy of Two-Dimensional Highly Luminescent Colloidal Nanostructures Determined from Combined Optical and Photoacoustic Spectroscopies.

Reduced dimensionality of structures such as 0D quantum dots, 1D nanorods, and 2D nanoplatelets is predicted to favor the creation of tightly bound excitons stable at room temperature, making experimental determination of the exciton binding energy ( R ) crucial for evaluating the performance of semiconductor nanoparticles. We propose a fully optical approach for R determination based on a complementary combination of photoacoustic and transmission spectra, using 5.5, 4.

Three-Photon Absorption of Coordination Polymer Transforms UV-to-VIS Thermometry into NIR-to-VIS Thermometry.

Lanthanide-based metal-organic frameworks (MOFs) and coordination polymers (CPs) attract much attention as candidates for optical ratiometric thermometry applications. Thus far, excitation of these materials was mainly performed in the ultraviolet that drastically limits their applicability as sensors, e.g.

Remote activation and detection of up-converted luminescence via surface plasmon polaritons propagating in a silver nanowire.

In this paper, we demonstrate remote activation and detection of the 2-photon up-conversion luminescence via surface plasmon polaritons propagating in a long silver nanowire. The hybrid nanostructure was assembled by locally depositing a submicron droplet of nanocrystal-containing colloidal solution on one of the ends of the metallic nanowire. When - using a classic confocal microscope - the second end of the nanowire, without the nanocrystals, is illuminated with infrared laser light, we observe strong emission from the same end.

Spectral Selectivity of Plasmonic Interactions between Individual Up-Converting Nanocrystals and Spherical Gold Nanoparticles.

We experimentally demonstrate strong spectral selectivity of plasmonic interaction that occurs between α-NaYF₄:Er/Yb nanocrystals, which feature two emission bands, and spherical gold nanoparticles, with plasmon frequency resonant with one of the emission bands. Spatially-resolved luminescence intensity maps acquired for individual nanocrystals, together with microsecond luminescence lifetime images, show two qualitatively different effects that result from the coupling between plasmon excitations in metallic nanoparticles and emitting states of the nanocrystals. On the one hand, we observe nanocrystals, whose emission intensity is strongly enhanced for both resonant and non-resonant bands with respect to the plasmon resonance.

Spectrally-resolved third-harmonic generation and the fundamental role of O-HCl hydrogen bonding in O, T-cobalt(ii) tetraphenylmethane-based coordination polymers.

The reaction of a phosphonate-diester tetraphenylmethane-based tecton, tetrakis[4-(diethoxyphosphoryl)phenyl]methane, (L) with cobalt(ii) chloride afforded a centrosymmetric coordination polymer (CP), [L·2Co(HO)·2CoCl], 2-Cl, possessing simultaneously octahedral (O) and tetrahedral (T) metal centers. This material served as a model compound for the demonstration of factors influencing the spectral dependence of one of the nonlinear optical (NLO) phenomena, the third-harmonic generation (THG). The spectrally-resolved THG (SR-THG) measurements in the range from 1125 to 1750 nm revealed that a maximum of THG response is obtained when the fundamental beam is around 1300 nm.

Nonlinear-Optical Response of Prussian Blue: Strong Three-Photon Absorption in the IR Region.

The nonlinear-optical properties of Prussian Blue nanoparticles have been evaluated with the use of femtosecond Z-scan measurements in the 1350-1750 nm range. This well-known inorganic pigment having interesting magnetic and electrochemical properties was found to be an efficient near-IR three-photon absorber. The maximum of the effective three-photon cross section is as high as 4.

Application of Direct Current Atmospheric Pressure Glow Microdischarge Generated in Contact with a Flowing Liquid Solution for Synthesis of Au-Ag Core-Shell Nanoparticles.

A direct current atmospheric pressure glow microdischarge (dc-μAPGD) generated between an Ar nozzle microjet and a flowing liquid was applied to produce Au-Ag core-shell nanoparticles (Au@AgCSNPs) in a continuous flow system. Firstly, operating dc-μAPGD with the flowing solution of the Au(III) ions as the cathode, the Au nanoparticles (AuNPs) core was produced. Next, to produce the core-shell nanostructures, the collected AuNPs solution was immediately mixed with an AgNO₃ solution and passed through the system with the reversed polarity to fabricate the Ag nanoshell on the AuNPs core.

Determining the 3D orientation of optically trapped upconverting nanorods by in situ single-particle polarized spectroscopy.

An approach to unequivocally determine the three-dimensional orientation of optically manipulated NaYF4:Er(3+),Yb(3+) upconverting nanorods (UCNRs) is demonstrated. Long-term immobilization of individual UCNRs inside single and multiple resonant optical traps allow for stable single UCNR spectroscopy studies. Based on the strong polarization dependent upconverted luminescence of UCNRs it is possible to unequivocally determine, in real time, their three-dimensional orientation when optically trapped.