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.

Pr doped NaYF and LiYF nanocrystals combining visible-to-UVC upconversion and NIR-to-NIR-II downconversion luminescence emissions for biomedical applications.

Lanthanide-doped fluoride nanocrystals (NCs) are known to exhibit unique optical properties, such as upconversion and downconversion luminescence (UCL and DCL), which can be employed for various applications. In this work, we demonstrate that by doping praseodymium(III) and ytterbium(III) ions (Pr and Yb) into a nanosized fluoride matrix ( NaYF and LiYF), it is possible to combine their UCL and DCL properties that can be concurrently used for biomedical applications. In particular, the emissive modes combined in a single nanoparticle co-doped with Pr and Yb include DCL emission (excited at 980 nm and peaked at 1320 nm), which can be used for near infrared (NIR) DCL bioimaging in the NIR-II window of biological tissue transparency (∼1000-1350 nm) and UCL emission (excited at 447 nm and peaked at 275 nm) that can be employed for germicide action ( irradiation by light in the UVC range).

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.

Polymeric Nanocarriers with Luminescent Colloidal Nanoplatelets as Hydrophilic and Non-Toxic Two-Photon Bioimaging Agents.

Introduction: Semiconductor nanoplatelets (NPLs) are promising materials for nonlinear optical microscopy since they feature good two-photon absorption (TPA) properties, narrow photoluminescence spectra and high quantum yields of luminescence. Nevertheless, the use of semiconductor NPLs is inevitably connected with concerns about heavy metal ion toxicity and their intrinsically hydrophobic character.

Methods: Our contribution focuses on the design and engineering of coloidal bionanomaterial consisting of two-dimensional highly luminescent CdSe semiconductor NPLs loaded into spherical and homogeneous polymeric nanocarriers (NCs) based on poly(ethylene oxide) and poly(propylene oxide) block co-polymer.

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.

The role of l-cysteine and introduced surface defects in reactive oxygen species generation by ZnO nanoparticles.

The synthesis and surface functionalization of ZnO nanoparticles were performed, with attention being paid to the possible bio-related applications in light-triggered reactive oxygen species generation. l-Cysteine molecules possessing sulfur atoms with high affinity to the ZnO surface proved to be interesting ligands, providing the improvement of the colloidal stability of the nanoparticles in aqueous solutions, and enhancing the efficiency of reactive oxygen species generation for antibacterial and photodynamic-based cancer treatment applications. Depending on the amount of the sulfur-containing ligands available for bonding to the ZnO nanoparticles, the ion exchange process occurring at the ZnO surface was observed.

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.

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.

Uniting Ruthenium(II) and Platinum(II) Polypyridine Centers in Heteropolymetallic Complexes Giving Strong Two-Photon Absorption.

New trinuclear RuPt2 and heptanuclear RuPt6 complex salts are prepared by attaching Pt(II) 2,2':6',2"-terpyridine (tpy) moieties to Ru(II) 4,4':2',2":4",4"'-quaterpyridine (qpy) complexes. Characterization includes single crystal X-ray structures for both polymetallic species. The visible absorption bands are primarily due to Ru(II) → qpy metal-to-ligand charge-transfer (MLCT) transitions, according to time-dependent density functional theory (TD-DFT) calculations.

Beyond Single-Wavelength SHG Measurements: Spectrally-Resolved SHG Studies of Tetraphosphonate Ester Coordination Polymers.

Powder second-harmonic generation (SHG) efficiencies are usually measured at single wavelengths. In the present work, we provide a proof of concept of spectrally resolved powder SHG measured for a newly obtained series of three non-centrosymmetric coordination polymers (CPs). CPs are constructed from tetrahedral linker-tetraphenylmethane-based tetraphosphonate octaethyl ester and cobalt(II) ions of mixed, octahedral (Oh), and tetrahedral (Td), geometries and different sets of donors (CoO6 vs CoX3O).

The influence of stabilizers on the production of gold nanoparticles by direct current atmospheric pressure glow microdischarge generated in contact with liquid flowing cathode.

Gold nanoparticles (Au NPs) were prepared by direct current atmospheric pressure glow microdischarge (dc-μAPGD) generated between a miniature argon flow microjet and a flowing liquid cathode. The applied discharge system was operated in a continuous flow liquid mode. The influence of various stabilizers added to the solution of the liquid cathode, i.

Tip enhancement of upconversion photoluminescence from rare earth ion doped nanocrystals.

We present tip-enhanced upconversion photoluminescence (PL) images of Er(3+)- and Yb(3+)-doped NaYF4 nanocrystals on glass substrates with subdiffraction spatial resolution. Tip-sample distance dependent measurements clearly demonstrate the near-field origin of the image contrast. Time-resolved PL measurements show that the tip increases the spontaneous emission rate of the two emission channels of Er(3+) in the visible region.