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The experimental determination of the velocity of a colloidal nanoparticle (vNP) has recently became a hot topic. The thermal dependence of vNP 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 vNP although they have only been capable of determining it at room temperature. In this work, we demonstrate that it is possible to determine the temperature dependence of the diffusive velocity of a single colloidal nanoparticle by analyzing the temperature dependence of optical forces. The comparison between experimental results and theoretical predictions allowed us to discover the impact that the anomalous temperature dependence of water properties has on the dynamics of colloidal nanoparticles in this temperature range.

Colloidal, oil-core polymer-shell nanocapsules (NCs), loaded with both upconversion NaYF4:Yb,Er nanoparticles (NPs) and CdSe quantum dots (QDs), were prepared via nanoemulsification/solvent-evaporation methods. Transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) techniques were used to comprehensively determine the structure, phase composition, and morphology of the NCs. Furthermore, we demonstrated that by simultaneously loading the hybrid fluorophores into the multimodal NCs, it is possible to combine their mechanistically distinct one- and two-photon luminescence properties. The two-photon absorption cross-section obtained at 850 nm for a single capsule was equal to 2.5 × 104 GM (Goeppert-Mayer units). Importantly, cytotoxicity studies indicated the potential of the co-encapsulated NPs and QDs for fluorescence imaging in biological specimens. We conclude that such non-toxic water-dispersible multifunctional nanohybrids represent a promising platform for advanced one- and two-photon induced fluorescence bioimaging and photonic sensing technologies.

The laser controlled transistor effect at the dielectric/vacuum interface characterized by tunable current–voltage characteristics was studied in this work. An Yb3Al5O12 nanoceramic was used as the...

The designed interaction between up-converting nanoparticles and photosensitizers allows for near infrared triggered photodynamic therapy. Depending on their optical properties and spatial arrangement the light energy harvested by the nanoparticles can be transferred to the neighbor photosensitizer molecules via static- or dynamic-type interactions. To study the possibility of photodynamic effect enhancement in such a hybrid system we have engineered polymeric nanocapsules with a structured double compartment core feasible for constraining hydrophobic up-converting NaYF4:Er3+,Yb3+ nanoparticles and hydrophilic Rose Bengal molecules. Due to the chosen encapsulation method there was no necessity for surface functionalization of nanoparticles nor any chemical modification of photosensitizers, thus both of the chromophores exhibited unchanged optical properties. We have obtained a series of nanocarrier samples having a constant amount of up-converting nanoparticles and an increasing amount of Rose Bengal molecules for detailed spectroscopic (up-conversion emission spectra and kinetics) and theoretical (density functional theory based calculations) studies on their mutual interaction. The obtained results show the possibility of both up-conversion emission enhancement in the presence of Rose Bengal molecules, and static-type energy transfer from nanoparticles to photosensitizers. The applicability of the obtained nanocapsules in photodynamic based cancer treatments was further evaluated based on the reactive oxygen species, including singlet oxygen, generation upon near infrared excitation. Additionally, the other surface of the nanocontainers was functionalized with PEG-ylated hyaluronic acid to assure the “stealth” effect and selective accumulation in cancer cells.

Katarzyna Celina Nawrot,1 Jan Kazimierz Zareba,1 Monika Toporkiewicz,2 Grzegorz Chodaczek,2 Dominika Wawrzynczyk,1 Julita Kulbacka,3 Urszula Bazylinska,4 Marcin Nyk1 1Advanced Materials Engineering and Modelling Group, Faculty of Chemistry, Wroclaw University of Science and Technology, Wroclaw, 50-370, Poland; 2Łukasiewicz Research Network - PORT Polish Center for Technology Development, Wroclaw, 54-066, Poland; 3Department of Molecular and Cellular Biology, Faculty of Pharmacy, Wroclaw Medical University, Wroclaw, 50-556, Poland; 4Department of Physical and Quantum Chemistry, Faculty of Chemistry, Wroclaw University of Science and Technology, Wroclaw, 50-370, PolandCorrespondence: Urszula BazylinskaDepartment of Physical and Quantum Chemistry, Faculty of Chemistry, Wroclaw University of Science and Technology, Wybrzeze Wyspianskiego 27, Wroclaw, 50-370, PolandTel +48 713202183Email urszula.bazylinska@pwr.edu.plMarcin NykAdvanced Materials Engineering and Modelling Group, Faculty of Chemistry, Wroclaw University of Science and Technology, Wroclaw, 50-370, PolandTel +48 713202316Email marcin.nyk@pwr.edu.plIntroduction: 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. The biocompatibility and usefulness of the NPLs-loaded polymeric NCs in two-photon induced bioimaging was demonstrated invitroby cytotoxicity and two-photon microscopic studies using eukaryotic (normal fibroblasts and cancer ovarian) cells.Results: The encapsulated NPLs maintain their intensive and spectrally narrow photoluminescence, as well as preserve good TPA properties, while the surrounding polymer shell imparts hydrophilic character and non-toxicity towards eukaryotic cells. Specifically, TPA cross-sections of the colloidal NCs loaded with NPLs show large values reaching up to 2.0 × 108 GM, with simultaneously two-photon brightness reaching 2.2 × 107 GM at 870 nm. MTT proliferation assay performed on cell lines treated with encapsulated NPLs revealed at least 70% viability of normal human gingival fibroblast (HGF) and cancer ovarian (MDAH-2774) cells, while the results of multiphoton imaging of murine (L-929) fibroblasts suggest that the encapsulated NPLs are capable of labelling the target cells enabling their visualization.Conclusion: As a result, we obtained water dispersible and temporally stable hydrophilic NPLs-loaded NCs that offer excellent, both one- and two-photon excited fluorescence preserving optical properties of the raw hydrophobic and colloidal NPLs. The biological responses upon eukaryotic cells indicate that the encapsulation process protects cells from the toxic influence of cadmium simultaneously preserving the unique multiphoton properties of the active cargo which opens a promising perspective for its application in multiphoton cancer bioimaging excited at the “optical transmission window” of biological tissues in near-infrared range.Keywords: semiconductor biomaterials, two-photon luminescence, nanodiagnostic agents, nonlinear optical properties, fibroblasts, cancer ovarian cells, laser diagnostics

The CsPbX3 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. The two-photon absorption cross-section &sigma, 2 values calculated from femtosecond Z-scan measurements were compared with those obtained based on the two-photon excited emission technique. These two techniques were shown to be equivalent with the cross-section values calculated per molar mass of CsPbX3 perovskite being in the range of 10&ndash, 200 GM depending on the halide anions X&minus, The &sigma, 2 values recalculated for the mole of the NCs were in the range of 104&ndash, 105 GM, which is in good agreement with values previously reported elsewhere and the &sigma, 2/M parameter was in the range of 0.01 to 0.33. This study shows the perovskite NCs to be a good nonlinear material with the third-order nonlinear optical susceptibility &chi, (3) of the NCs on the order of 10&minus, 11 esu.

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. For photocatalysis studies, we performed methylene blue (MB) absorption measurements under irradiation in the presence of CdS-Au NPs. After 1 h of light exposure, we observed the absorbance decrease to about 35% and 10% of the initial value for the CdS-5Au and CdS-7.5Au (the hybrid NPs obtained in a presence of 5.0 and 7.5 mM Au), respectively, which indicates MB reduction caused by electrons effectively separated from holes on metal surface. In further similar photocatalysis experiments, we measured bovine serum albumin (BSA) integrated photoluminescence intensity quenching in the presence of CdS-Au NPs, with a 50% decrease being obtained for CdS-2.5Au NPs and CdS-5Au NPs, with a faster response rate detected for the system prepared with a higher Au concentration. The results suggest hole-driven reactive oxygen species (ROS) production, causing BSA degeneration. Finally, we performed two-photon excited emission (TPEE) measurements for CdS-5Au NPs, obtaining their two-photon absorption (TPA) cross-section values up to 15.8 &times, 103 GM (Goeppert-Mayer units). We conclude that the obtained water-soluble CdS-Au NPs exhibit potential triple functionalities as photocatalysts for reduction and oxidation reactions as well as materials for two-photon absorption applications, so that they may be considered as future theranostics.

Quantitative comparison of emission intensity between lanthanide doped upconverting (UC) nanoparticles is critical to evaluate the impact of host matrix and nanocrystal size, active- and passive- dopants, core-shell chemical architecture, surface biofunctionalization and others, which are typically a subjects to optimization. While relative luminescence intensity has been commonly used for that purpose, quantum yield (QY) is another accurate measure, because here, number of UC emission photons is normalized to the number of photons being absorbed. However, this type of measurements have been hindered by limited availibility of commercial instrumentation. Here we show a novel, simple and affordable UCQY setup design and versatilely characterize its performance using Yb3+ and Ho3+ co-doped colloidal NaYF4 nanoparticles dispersed in chloroform. The UCQY showed a liner dependence on excitation intensity, and reached up to 0.41% and 0.25% for the 2% Ho3+, 20% Yb3+ and 0.1% Ho3+, 20% Yb3+ materials, respectively. Interestingly, the UCQY values depend on the selection of reference material and concentration of NPs. In particular, the un-doped reference NPs of the same diameter as the sample NPs show higher UCQY values than the ones obtained for the pure solvent. Moreover, UCQY depend on the concentration of the NPs. These two effects were related to the scattering of photoexcitation beam in the sample and reference materials. Additionally, no saturation of power dependent UC was seen up to ~270 W/cm2 excitation intensities, which we relate to the photoexcitation methodology. In opposite to the Continuous Wave photoexcitation, we used Pulse Width Modulation of photoexcitation intensity, and confirm such behavior with a simple, time – resolved differential rate equations based model. These findings and reliable UCQY instruments are important to quantitatively compare and further optimize the performance of UCNPs.

Spectrally resolved femtosecond nonlinear optical study in the range of 950–1350 nm has been conducted for three colloidal NaYF4:Yb,Er/CdSe hybrid nanostructures, which differ in the size of the surface decorating CdSe quantum dots (6.6, 6.8 and 7.0 nm). The two-photon absorption cross sections σ2 of the hybrid nanoconstructs are as large as 2.55 × 105 GM in the near-infrared region (∼1150 nm); their very good nonlinear absorption properties being imparted by the CdSe nanoparticles. Further, we demonstrate that by merging NaYF4:Yb,Er and the CdSe nanoparticles into hybrid materials, it is possible to combine their mechanistically distinct two-photon-induced luminescence properties. Indeed, we report the switching of multi-modal luminescence of the colloidal NaYF4:Yb,Er/CdSe hybrid nanomaterials, in which both constituents can be excited separately or simultaneously, depending on the selection of the excitation source. The emissive modes include visible up-conversion and near-infrared emission of erbium(III) ions doping the NaYF4 core, as well as one- or two-photon induced band-gap luminescence of the outer layer, comprising the CdSe quantum dots. Toggling between the emission modes is achieved by single or dual beam excitation of the respective components, using a continuous wave 980 nm laser diode for NaYF4:Yb,Er nanoparticle emission, and femtosecond laser near-infrared pumping for CdSe quantum dot band-gap emission. The Forster resonance energy transfer between both optically active components of the synthesized hybrid nanostructures, i.e. up-converting nanoparticles (donor) → quantum dots (acceptor), has been determined to have 2.5% to 6% efficiency, depending on the size of the participating CdSe nanoparticles. Finally, we show that the multimodal luminescence properties of these hybrid nanomaterials can be potentially employed for 2D anti-counterfeiting applications.

The emulsification process leading to up-converting NaYF4:Er3+,Yb3+ NPs encapsulation, was performed using a modified water/oil/water double emulsion evaporation method, where poly(lactic-co-glycolic acid) was used as biocompatible polymer. Span 80 and Cremophor A25 were applied as non-ionic surfactants and dichloromethane as oily phase. The use of trioctylphosphine oxide ligands for the synthesis of up-converting NaYF4:Er3+,Yb3+ NPs allowed to obtain spherical particles with sizes below 10 nm, what further facilitated the efficient encapsulation process. Those newly designed nanosystems were subjected to analysis of their morphology, colloidal stability and optical properties by: dynamic light scattering, ζ-potential, atomic force microscopy, transmission electron microscopy and measuring the up-conversion emission spectra of free and loaded NaYF4:Er3+,Yb3+ NPs. The encapsulated NaYF4:Er3+,Yb3+ NPs showed increased colloidal stability for a long period of 60 days of storage in different conditions. Simultaneously, the encapsulation process did not significantly influenced their optical properties and strong visible emission could be observed upon nearinfrared excitation.

The ligand induced chirality in semiconducting nanoparticles has recently gained special attention, due to possible application of chiral nanoparticles as optically active probes in enantioselective bio-sensing. However, the exact mechanisms of chiral organic ligands interaction with quantum dots surfaces are still not fully described. We have performed ligand exchange procedure in order to obtain water soluble CdSe QDs functionalized with left- and right-handed enantiomers of penicillamine molecules and the influence of such post-synthetic surface treatment on the optical properties of CdSe QDs with respect to their size has been investigated. In particular, picosecond and nanosecond time scale kinetics revealed strong hole trapping at the thiol molecules near to the quantum dots surfaces. Additionally, possible applications of chiral drug discrimination are shown for L- and D-penicillamine functionalized CdSe quantum dots.

The concentration dependent up-conversion luminescence of 0.1; 0.2; 0.5; 1; 1.5; 2; 3; 4 and 5% Ho3+ and 20% Yb3+ co-doped β-NaYF4 colloidal nanocrystals have been studied. The obtained nanocrystals were homogenous in size and shape, as well as the crystallographic structure was pure. The absorption spectra, upconversion lifetimes, up-conversion emission and Quantum Yield power dependence have been measured to estimate the optimum doping concentration of Ho3+ ions. The experimental results were supported by the calculations based on Judd-Ofelt theory, in order to quantify the oscillator strengths in absorption and luminescence, excited-state radiative lifetimes, energy-transfer probabilities, and to estimate the quantum efficiencies of this interesting material. We have observed evident trend in rise- and luminescence decay profiles with rising Ho3+ activator concentration, and the 1–2% Ho3+ ions doping was found to be the most efficient nanophosphors.

Comprehensive studies on the electronic properties and spectral dependencies of the third-order nonlinear optical properties of quantum-confined tetragonal chalcopyrite AgInS2 and its non-stoichiometric cubic spinel AgIn5S8 with reference to their corresponding Zn2+ alloyed compounds i.e. AgInS2/ZnS and AgIn5S8/ZnS are presented in this work. Nonlinear refraction and nonlinear absorption in the quantum-confined nanocrystals were measured in a wide range of wavelengths (550–1200 nm) using the Z-scan technique. The results revealed the presence of strong two-photon absorption bands in the near-infrared range for both compounds. The impact of Zn2+ ion alloying was also investigated for both compounds revealing a significant increase of the cubic nonlinearity for the chalcopyrite quantum dots and a negligible change for the spinel-like quantum dots which was discussed as a consequence of different surface reconstruction mechanisms of the tetragonal and cubic nanocrystals. The cubic nonlinearity of the quantum dots is discussed in terms of electronic properties and linear dielectric function dispersions of both systems obtained within the density functional theory. Kinetics of the two-photon excited state recombination was investigated with the femtosecond time-resolved photoluminescence spectroscopy revealing the complex character of electronic relaxation in both systems. The results indicate that the optical properties of the tetragonal AgInS2 and cubic AgIn5S8 quantum dots are much better suited for the steady-state as well as time-resolved multiphoton fluorescence techniques utilized commonly for bio-sensing applications than their CuInxSy homologues.

The two-photon absorption of water soluble CdS tetrapods, stabilized with a racemic mixture of chiral ligands, was measured using two techniques: open-aperture Z-scan and two-photon excited emission. The investigated CdS tetrapods showed two-photon absorption in the wavelength range 575–875 nm, with the maximum value of 7900 GM at 625 nm. Thanks to the high luminescence quantum yield, and relatively strong two-photon absorption, the CdS tetrapods showed intense two-photon excited emission upon near-infrared excitation with two-photon excitation action cross-section equal to 3200 GM and 420 GM at 650 nm and 700 nm, respectively. An evident blue shift of the two-photon absorption maxima with respect to the one-photon spectra at the wavelengths multiplied by two was observed, and discussed based on the reported theoretical calculation for CdS quantum dots with tetrahedral symmetry. Since CdS tetrapod arms show low electron and hole densities, they do not contribute significantly to the values of the two-photon absorption cross-section. The performed investigation of the optical properties of these water soluble colloidal nanoparticles indicates their potential applications in nonlinear bioimaging.

In response to the growing number of life-threatening infections caused by opportunistic Candida albicans fungi we have examined and discussed the effect of glucose and human serum on the efficiency of photosensitization of C. albicans cells with 5-aminolevulinic acid (5-ALA) used as a precursor of protoporphyrin IX (PpIX). We used 630 nm laser diode as an excitation source to enhance the penetration depth and diminish unwanted light scattering, additionally the experiments were performed in planktonic and biofilm cultures to differentiate the results obtained for cells showing various phenotypic characteristics. Based on performed experiments it became obvious that the incubation of C. albicans fungal cells with 5-ALA in the presence of glucose caused a significant increase in concentration of intracellular PpIX, resulting in a higher efficacy of photo-toxic effect. The observed results were rationalized by the role of glucose as an energy source, which supported the active transport of 5-ALA into cells. In contrary to glucose, the presence of human serum caused a significant reduction in PpIX concentration in C. albicans cells with exogenous delivery of 5-ALA, resulting in a less efficient photo-fungicidal effect. In general, the obtained results contributed to the current search for efficient, light activated anti-fungal treatments of high efficiency.

The optical properties of small band gap, colloidal quantum dots are presented, with the special emphasis put on the measurements of their nonlinear optical properties in the infrared region of spectra. In particular, two types of colloidal quantum dots (PbS and PbSe), with the first exciton absorption band maxima in the near-infrared region of spectra, were investigated using a tunable femtosecond laser system and the Z-scan technique. The measurements of closed- and open-aperture Z-scan traces allowed for the calculation of real and imaginary parts of cubic nonlinearity, which were presented as appropriate cross sections used to characterize the nonlinear refractive and absorptive properties of the studied quantum dots. The maximum two-photon absorption cross section values taken for a single quantum dot were found to be ∼2400 GM (Goeppert-Mayer units) at 1300 nm and ∼15 500 GM at 1700 nm, for PbS and PbSe QDs, respectively. PbS quantum dots showed two-photon induced emission upon infrared excitation. T...

I report surface modification of up-converting, Er3+ and Yb3+ co-doped β-NaYF4 nanoparticles with four types of chiral molecules with proven molecular chiral recognition abilities: L-cysteine, L-penicillamine, L-arginine and L-glutathione. The presence of chiral ligands near to the nanoparticle surfaces was confirmed based on Fourier transform infrared spectroscopy and circular dichroism measurements. The performed post synthetic treatment of nanoparticle surfaces led to stable water solutions, and the best results regarding the long term colloidal stability were found for nanoparticles functionalized with L-penicillamine. The selected chiral molecules were also found to strongly influence the spectroscopic properties of NaYF4:Er3+,Yb3+ nanoparticles, including the change in power dependence slopes for blue, green and red emission and luminescence lifetimes. Nevertheless, the high up-conversion emission intensity was preserved after functionalization. The obtained results open up new perspectives for possible applications of up-converting β-NaYF4 NPs as optical markers in chiral recognition and sensing of chiral drugs.

We investigated new development in photodynamic therapy (PDT), aiming at enhanced tumor selectivity and biocompatibility, which included application of a third-generation photosensitizing agent, i.e. xanthene-origin Rose Bengal (RB) co-encapsulated with up-converting NaYF4 nanoparticles (NPs) co-doped with lanthanide ions: Er3+ (2%) and Yb3+ (20%). The hybrid fluorophores were applied as components of double core nanocarriers (NCs) obtained by double (multiple) emulsion solvent evaporation process. Next, to improve the biocompatibility and photodynamic activity, biodegradable polymer: poly(lactide-co-glycolide) - PLGA and non-ionic surfactants with different hydrophobicity: Span 80 and Cremophor A25, were used. After the engineering process, controlled by dynamic light scattering (DLS) measurements, ζ-potential evaluation, transmission electron and atomic force microscopy (TEM and AFM) imaging, as well as optical analysis provided by measurements of the up-conversion emission spectra and luminescence kinetics for encapsulated only NaYF4:Er3+,Yb3+ NPs and co-encapsulated RB + NaYF4:Er3+,Yb3+ molecules, spherical polyester NCs with average size

Multilayer nanocarriers loaded with optically activated payloads are gaining increasing attention due to their anticipated crucial role for providing new mechanisms of energy transfers in the health-oriented applications, as well as for energy storage and environmental protection. The combination of careful selection of optical components for efficient Forster resonance energy transfer, and surface engineering of the nanocarriers, allowed us to synthesize and characterize novel theranostic nanosystems for diagnosis and therapy of deep-seated tumors. The cargo, constrained within the oil core of the nanocapsules, composed of NaYF4 :Tm+3 , Yb+3 up-converting nanoparticles together with a second-generation porphyrin-based photosensitizing agent-Verteporfin, assured requisite diagnostic and therapeutic functions under near-IR laser excitation. The outer polyaminoacid shell of the nanocapsules was functionalized with a ligand-poly(l-glutamic acid) functionalized by PEG-ylated folic acid-to ensure both a "stealth" effect and active targeting towards human breast cancer cells. The preparation criteria of all nanocarrier building blocks meet the requirements for sustainable and green chemistry practices. The multifunctionality of the proposed nanocarriers is a consequence of both the surface-functionalized organic exterior part, which was accessible for selective accumulation in cancer cells, and the hydrophobic optically active interior, which shows phototoxicity upon irradiation within the first biological window.

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. Both the experimental measurements and numerical calculations, performed in the frame of density functional theory, showed that the surface adhered OH− and SH− groups play a dominant role in the formation of the reactive oxygen species in the presence of ZnO nanoparticles in solution upon ultraviolet and blue light excitation. It was also observed that the efficiency of the reactive oxygen species generation process may also be enhanced by the adhesion of the SH− groups onto the surface of the ZnO clusters.

Concomitant amplified spontaneous emission (ASE) and F\"orster resonance energy transfer (FRET) are investigated in electrospun light-emitting fibers. Upon dye-doping with a proper FRET couple system, free-standing fibrous mats exhibit tunable FRET efficiency and, more importantly, tailorable threshold conditions for stimulated emission. In addition, effective scattering of light is found in the fibrous material by measuring the transport mean free path of photons by coherent backscattering experiments. The interplay of ASE and FRET leads to high control in designing optical properties from electrospun fibers, including the occurrence of simultaneous stimulated emission from both donor and acceptor components. All tunable-optical properties are highly interesting in view of applying electrospun light-emitting materials in lightening, display, and sensing technologies., Comment: 32 pages, 13 figures

Bichromatic stimulated emission is achieved from electrospun hierarchical heterostructures with physically prevented donor quenching., We present stacked organic lasing heterostructures made by different species of light-emitting electrospun fibers, each able to provide optical gain in a specific spectral region. A hierarchical architecture is obtained by conformable layers of fibers with disordered two-dimensional organization and three-dimensional compositional heterogeneity. Lasing polymer fibers are superimposed in layers, showing asymmetric optical behavior from the two sides of the organic heterostructure, and tailored and bichromatic stimulated emission depending on the excitation direction. A marginal role of energy acceptor molecules in determining quenching of high-energy donor species is evidenced by luminescence decay time measurements. These findings show that non-woven stacks of light-emitting electrospun fibers doped with different dyes exhibit critically-suppressed Förster resonance energy transfer, limited at joints between different fiber species. This leads to the obtaining of hybrid materials with mostly physically-separated acceptors and donors, thus largely preventing donor quenching and making it much easier to achieve simultaneous lasing from multiple spectral bands. Coherent backscattering experiments are also performed on the system, suggesting the onset of random lasing features. These new organic lasing systems might find application in microfluidic devices where flexible and bidirectional excitation sources are needed, optical sensors, and nanophotonics.

Hydrophobic CdSe x Te 1− x quantum dots with near infrared emission in the 700–750 nm range were synthesized by a wet chemistry technique. Their nonlinear optical properties were studied using Z-scan technique with a tunable femtosecond laser system. The peak value of the two-photon absorption cross section was found to be ∼2400 GM at 1400 nm. To demonstrate a possible way of utilizing the CdSe x Te 1− x quantum dots in aqueous environment we describe here a convenient method of preparation of Brij 58® micellar systems loaded with the quantum dots. The obtained nanoconstructs were characterized using optical spectroscopy, TEM and DLS. The micelles colloidal stability, and the influence of the encapsulation process on the spectroscopic properties of the quantum dots are discussed. In particular, we have observed a 60 nm blue-shift of the emission maxima upon loading quantum dots inside the micelles.

We demonstrate the use of thermal decomposition reaction to obtain Ga 2 O 3 nanoparticles with average size around 5 nm. The obtained nanoparticles presented a good colloidal stability and high optical transparency. We were also able to incorporate Eu 3+ and Tb 3+ ions inside the crystal host. The synthesized nanomaterials exhibited dual mode emission upon UV excitation, consisting of a broad band in the blue region and a characteristic series of sharp lines. The former resulted from donor–acceptor pairs recombination in Ga 2 O 3 host, while the latter from 4f–4f electronic transitions in lanthanide ions. For fuller optical characterization of the obtained nanoparticles, we have performed wide wavelength range Z-scan studies, and calculated the values of nonlinear absorption cross-sections. Gallium (III) oxide nanoparticles showed two-photon absorption in the range between 500 nm and 700 nm, with molecular weight scaled nonlinear optical parameters exceeding the values for other lanthanide-doped nanoparticles of similar size.

We report a comprehensive study on the influence of solvent and organic ligands on the up-converted emission characteristics of NaYF4 nanowires. We have modified the hydrothermal reaction procedure, and used a “microwave flash heating method” to obtain 1.5 μm long and 100 nm wide up-converting NaYF4 nanowires. As-synthesized particles were dispersed in cyclohexane, and a ligand removal procedure has been performed leading to nanowires soluble in water and heavy water. The infrared emission of Er3+ ions was quenched through coupling to the vibrational modes of water molecules and the values of slopes of double logarithmic plots of power dependencies were changed. Besides the spectroscopic characterization of colloidal solutions of NaYF4 up-converting nanowires, we have also performed single particle studies of steady-state emission and luminescence kinetics. In the case of solvent-free separated particles, the ligand molecules provided the main nonradiative depopulation channels, and efficiently shortened the luminescence lifetimes. The output luminescence color also varied for colloidal solutions and single particle studies, which can be of importance for imaging and single particle tracking applications.

The influence of mono-positive alkali ions (Li+, Na+ and K+) on the growth processes, crystal structure and spectroscopic properties of Gd2O3 colloidal nanoparticles doped with Eu3+ ions was investigated. The size of an alkali dopant ionic radius, with respect to that of Gd3+ ions, and the relative concentrations of the alkali ions against that of Gd3+ were found to have a significant impact on the morphology of the obtained Gd2O3 nanoparticles which could be tuned from ~10 nm nanospheres, through ~40 nm nanotripods and nanotriangles, leading to over 50 nm sized, square-like shaped nanoparticles. The observed evolution of the Gd2O3 crystal structure upon alkali ion doping allowed finding of the maxima of the impurity ion concentration inside the Gd2O3 crystal lattice. The distortion of the crystal structure of Gd2O3 introduced by Li+, Na+ or K+ doping was also related to the ratio of electric to magnetic dipole transitions in Eu3+ ions, the shape of the 5D0 → 7F0 transition, and the 5D0 energy level luminescence lifetime values. The obtained results show the possibility of using intentional impurities to tune the morphology of colloidal Gd2O3 NPs, and simultaneously of using the luminescence of Eu3+ ions for sensing the changes in local surroundings.

The spectral tuning range of dye lasers is closely associated with the gain profile provided by the utilized luminescent compound. Here, we present the results of studies aimed at broadening the wavelength tuning range in distributed feedback (DFB) lasers, made up of polymeric layers doped with a mixture of two complementary dyes. We have used the 3-(2,2-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DCNP) luminescent dye, showing stimulated emission in its crystalline form, and the Rhodamine 700 (Rh700) laser dye, which is red-shifted in luminescence relative to DCNP, both doped into a poly(methyl methacrylate) (PMMA) host matrix. We have investigated the relationships between the additives' relative weight to weight ratios and their ability to exhibit a nonradiative energy transfer process that is inherent with a luminescence quenching of the shorter wavelength emitter, the so-called donor. This in turn directly reflects the efficiency of simultaneous utilization of both dyes’ emission bands for lasing. By the proper engineering of the gain material composition, it was possible to broaden the DFB lasing tuning spectral range up to 125 nm, which is twice as much compared to the DCNP/PMMA material, i.e. without addition of Rh700. Finally, the presented results have shown that additional random feedback, which is detrimental to the DFB lasing, originating from the presence of DCNP crystals within the polymeric bulk, can be effectively suppressed by the superposition of a temporary DFB resonator.

Nonlinear optical properties of semiconducting CdSe quantum rods (QRs), with three various aspect ratios, were examined in a wide wavelength range using femtosecond Z-scan technique. The two-photon absorption cross section σ2 was found to be as large as 164 000 GM at the wavelength of 750 nm: about 4 times larger than that expected for CdSe quantum dots of the same mass. On the basis of the obtained dispersion of the two-photon absorption cross section, we have selected wavelength ranges for optimal excitation of two-photon-induced emission. We have also studied the luminescence kinetics using degenerate pump–probe and time-correlated single-photon counting techniques. A strong influence of semiconducting CdSe rods morphology on their steady-state and time-resolved optical properties was found.

Synthesis, crystal structure, morphology and optical properties of three various NaYF 4 nanoparticle systems co-doped with Tm 3+ and Yb 3+ ions have been investigated. Characterization of ultrasmall (size ∼8 nm), small (∼25 nm) NaYF 4 :2%Tm 3+ , 20%Yb 3+ nanoparticles and core–shell structures (NaYF 4 :20%Yb 3+ –NaGdF 4 :2%Tm 3+ ) synthesized according to two different protocols is presented. We have found that the up-conversion luminescence is strongly influenced by the nanoparticle size, internal structure and spatial distribution of active Tm 3+ ions. Further spectroscopic studies revealed significant fluorescence rise and decay time lengthening of the 1 G 4 energy level of Tm 3+ ions in NaYF 4 :20%Yb 3+ –NaGdF 4 :2%Tm 3+ core–shell nanoparticles. The formation of the core–shell structures was proven indirectly through the average crystalline size increase between the bare core and core–shell nanoparticles, the observed changes in EDX composition as well as variation of Tm 3+ ions luminescence properties.

The optical properties of lanthanide (Ln3+) ions were recognized many years ago in several important elds of science and technology. Lanthanide-doped crystal, glasses, and bers have been used as optically active materials for compact solid-state laser crystals (Geusic et al. 1964; Moncorge et al. 1999; Quarles et al. 1990), ber lasers (Digonnet 2001), TV tubes or lamp phosphors (Lakshmanan 2008), as well as IR quantum cutters (Esterowitz et al. 1968). The unique optical features of lanthanide-doped nanomaterials arise from the electronic conguration of optically active ions doped into the crystal matrix. The 4f-4f intra-congurational transitions are Laporte forbidden, and simultaneously the electrons at 4f energy levels are shielded by the lled higher orbitals. The consequences of forbidden character of electronic transitions observed in lanthanides are among others: low transition probability, and further long luminescence lifetimes, which vary between micro to milliseconds. These long decays facilitate ultrahigh sensitivity detection, since in time-resolved mode, the background free detection becomes possible. In addition, due to the weak interaction of electrons at 4f orbitals with the crystal eld of the host matrix, the absorption and emission lines are very narrow and occur in strictly dened spectral ranges, which on the other hand, enable the engineered design of multicolor emission and further multiplex detection.

An innovative approach for up-converting nanoparticles adaptation for bio-related and theranostic applications is presented. We have successfully encapsulated multiple, ~8 nm in size NaYF4 nanoparticles inside the polymeric nanocarriers with average size of ~150 nm. The initial coating of nanoparticles surfaces was preserved due to the hydrophobic environment inside the nanocapsules, and thus no single nanoparticle surface functionalization was necessary. The selection of biodegradable and sugar-based polyelectrolyte shells ensured biocompatibility of the nanostructures, while the choice of Tm3+ and Yb3+ NaYF4 nanoparticles co-doping allowed for near-infrared to near-infrared bioimaging of healthy and cancerous cell lines. The protective role of organic shell resulted in not only preserved high up-converted emission intensity and long luminescence lifetimes, without quenching from water environment, but also ensured low cytotoxicity and high cellular uptake of the engineered nanocapsules. The multifunctionality of the proposed nanocarriers is a consequence of both the organic exterior part that is accessible for conjugation with biologically important molecules, and the hydrophobic interior, which in future application may be used as a container for co-encapsulation of inorganic nanoparticles and anticancer drug cargo.

An approach to unequivocally determine the three-dimensional orientation of optically manipulated NaYF4:Er3+,Yb3+ 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. In single-beam traps, polarized single particle spectroscopy has concluded that UCNRs orientate parallel to the propagation axis of the trapping beam. On the other hand, when multiple-beam optical tweezers are used, single particle polarization spectroscopy demonstrated how full spatial control over UCNR orientation can be achieved by changing the trap-to-trap distance as well as the relative orientation between optical traps. All these results show the possibility of real time three-dimensional manipulation and tracking of anisotropic nanoparticles with wide potential application in modern nanobiophotonics, This work was supported by the Spanish Ministerio de Educación y Ciencia (MAT2013-47395-C4-1-R) and by Banco Santander for “proyectos de cooperación interuniversitaria” (2015/ ASIA/06). Patricia Haro-González thanks the Spanish Ministerio de Economía y Competitividad (MINECO) for the Juan de la Cierva program. Paloma Rodríguez-Sevilla thanks the Spanish Ministerio de Economía y Competitividad (MINECO) for the “Promoción del talento y su Empleabilidad en I+D+i” statal program. Dominika Wawrzyńczyk, Marcin Nyk and Marek Samoć acknowledge the support from the National Science Centre under grant DEC-2012/04/M/ST5/00340, by a statutory activity subsidy from the Polish Ministry of Science and Higher Education for the Faculty of Chemistry of Wroclaw University of Technology, as well as from the Foundation for Polish Science under START 2014 programme. This work has received funding from The Royal Society (IE130466). Mark D. Mackenzie acknowledges funding from EPSRC (grant no EP/J500227/1

We have investigated the influence of gold nanorods (Au NRs) proximity on the up-conversion luminescence of lanthanide-doped NaYF 4 nanoparticles (NPs). The measurements were performed on two different systems. We used solvent evaporation method to assemble NaYF 4 :2%Tm 3+ , 20%Yb 3+ NPs/Au NRs thin films, and colloidal water blend suspensions of mixed NaYF 4 :2%Tm 3+ , 20%Yb 3+ or NaYF 4 :2%Er 3+ , 20%Yb 3+ NPs with Au NRs. The coupling of the NaYF 4 :2%Tm 3+ , 20%Yb 3+ and NaYF 4 :2%Er 3+ , 20%Yb 3+ NPs emission with the surface plasmon of Au NRs was found to lead to effective modulation of Tm 3+ and Er 3+ ions luminescence. As the result of NPs and Au NRs being in close contact the rate of excitation could be increased, but also quenching by energy transfer and nonradiative relaxation has been observed.

The possibility of tuning between red, green and broadband white color of up-conversion was demonstrated in thermally 450 °C treated Yb/Er co-doped nano NaYF 4 phosphor. The color variability was studied by means of power dependence of luminescence, which exhibited unusual behavior. Large hysteresis, as well as discrepancy from a power law indicated the important role the increased heating played during the up-conversion in nano-sized materials.

Fluoride (NaYF4) nanocrystals (ca. 30 nm size) codoped with the rare earth ions Yb3+ and Er3+/Tm3+ were synthesized with a wet chemical technique and characterized by TEM and XRD. The materials wer...

Transparent, chloroform dispersed α -NaYF 4 nanocrystals doped with neodymium ions were synthesized and characterized. XRD and TEM measurement confirmed cubic structure of α -NaYF 4 of the nanoparticles (NPs). The absorption and emission spectra as well as 4 F 3/2 level fluorescence decay curves were measured in order to estimate the influence of Nd 3+ concentration in the matrix on the optical properties of the NPs. With the increase of Nd 3+ doping level, the Judd–Ofelt Ω 4 parameter as well as the spectroscopic Nd 3+ parameter X Nd = Ω 4 / Ω 6 was growing. In the same time the Ω 2 and Ω 6 were decreasing. Theoretical luminescence lifetimes of the 4 F 3/2 level equal to ∼300 μs were also calculated and compared with the experimental values to quantify the concentration quenching. Based on this comparison, quantum efficiency was found to vary systematically between ∼100% and 4% for Nd 3+ content increasing from 2 up to 25%.

At the core of luminescence color and lifetime Tuning of rare earth doped upconverting nanoparticles (UCNPs), is the understanding of the Impact of the particle architecture for commonly used sensitizer (S) and activator (A) Ions. In this respect, a series of core@Shell NaYF4 UCNPs doped with Yb3+ and Ho3+ ions are presented here, where the same dopant concentrations are distributed in different particle architectures following the scheme: YbHo core and YbHo@..., ...@YbHo, Yb@Ho, Ho@Yb, YbHo@Yb, and Yb@YbHo core-Shell NPs. As refealed by quantitative steady-state and time-resolved luminescence studies, the relative spatial Distribution of the A and S ions in the UCNPs and their protection from surface quenching has a critical Impact on ther luminescence characteristics. Although the increased amount of Yb3+ Ions boosts UCNP Performance by amplifying the Absorption, the Yb3+ ions can also efficiently dissipate the energy stored in the material through energy Migration to the surface, thereby reducing the Overall energy Transfer Efficiency to the activator ions. The results provide yet another proof that UC Phosphor chemistry combined with materials Engineering through intentional core@shell structures may help to fine-tune the luminescence Features of UCNPs for their specific future applications in biosensing, bioimaging, photovoltaics, and Display technologies.

We have been studying a number of nanosystems that either have potential applications in bioimaging and/or light-activated therapies, or are bioderived. The standard Z-scan technique was routinely used for most of the measurements which were carried out in a wide wavelength range, typically from ∼550 nm to 1.6 μm. The range of nanoparticles studied has included colloidal semiconductor nanoparticles (e.g. CdS, CdSe), plasmonic nanoparticles, metal clusters, lanthanide-doped fluoride and oxide nanocrystals as well as core-shell systems. Among the bioderived systems studied especially interesting one is that of protein amyloid fibers.Many of these materials exhibit nonlinear absorption features due not only to the typical two-photon absorption processes, but also due to multiple-photon absorption taking place, especially at longer wavelengths (e.g. three- four- and five-photon processes). On the other hand, absorption saturation processes may prevail or compete with multi-photon absorption in certain wavelength ranges in some of these materials, especially those characterized by broadband absorption due to surface plasmon excitation.

Wide wavelength range (550-1600 nm) measurements of nonlinear optical properties of ca. 5 nm CdS quantum dots (QDs) colloidal solution were performed using the Z-scan technique with femtosecond laser pulses at 1 kHz. Parameters characterizing nonlinear absorption and nonlinear refraction were determined. Nonlinear absorption has the character of a two-, three- and four-photon process depending on the wavelength range, with the values of the relevant coefficients peaking at 750 nm, 1200 nm and 1500 nm, respectively. The order of the nonlinear processes was confirmed by measurements of the integral luminescence intensity vs. input excitation intensity. Maxima of the multi-photon absorption bands correspond to the second absorption band of the QDs. The maximum value of the two-photon absorption cross-section σ2 was estimated to be 7.2 × 10(-47) cm(4) s per QD at 750 nm.

New complexes with six ferrocenyl (Fc) groups connected to ZnII or CdII tris(2,2′-bipyridyl) cores are described. A thorough characterisation of their BPh4− salts includes two single-crystal X-ray structures, highly unusual for such species with multiple, extended substituents. Intense, visible d(FeII)-π* metal-to-ligand charge-transfer (MLCT) bands accompany the π-π* intraligand charge-transfer absorptions in the near UV region. Each complex shows a single, fully reversible FeIII/II wave when probed electrochemically. Molecular quadratic nonlinear optical (NLO) responses are determined by using hyper-Rayleigh scattering and Stark spectroscopy. The latter gives static first hyperpolarisabilities β0 reaching as high as approximately 10−27 esu and generally increasing with π-conjugation extension. Z-scan cubic NLO measurements reveal high two-photon absorption cross-sections σ2 of up to 5400 GM in one case. DFT calculations reproduce the π-conjugation dependence of β0, and TD-DFT predicts three transitions close in energy contributing to the MLCT bands. The lowest energy transition has octupolar character, whereas the other two are degenerate and dipolar in nature, We thank the EPSRC for support (grants EP/D070732 and EP/G02099) and also the Fund for Scientific Research-Flanders (FWO-V, G.0312.08), the University of Leuven (GOA/2011/03), The Foundation for Polish Science (Welcome grant to M.S.), MCyT-FEDER (CTQ2005–01368, CTQ2008–02942) and Gobierno de Aragon-Fondo Social Europeo (E39). B.S.B. acknowledges the Beckman Institute of the California Institute of Technology for support.

NaYF4: 2%Er3+, 20%Yb3+ nanoparticles were synthesized through a wet chemical route. In order to transfer the nanoparticles from chloroform to aqueous solution an oleic acid to 3-mercaptopropionic acid ligand exchange process has been performed and optimized. The influence of temperature and atmosphere onto the NaYF4:2%Er3+, 20%Yb3+ nanoparticles water suspensions dispersibility and stability after replacing oleic acid with 3-mercaptopropionic acid ligands has been investigated. The results revealed an improvement of nanoparticles water suspension transparency and luminescence yield after ligand exchange process performed under inert atmosphere and at elevated temperature.

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.

Comprehensive studies on the spectral dependencies of third-order nonlinear optical properties and one/two-photon excited time-resolved luminescence of quantum-confined ternary CuInS2/ZnS core/shell heterostructures with reference to their corresponding uncoated CuInS2 cores are presented in this work. Nonlinear refraction and nonlinear absorption in the quantum confined type-I core/shell CuInS2/ZnS and their corresponding CuInS2 cores were measured over a wide range of wavelengths (550–1500 nm) using the Z-scan technique. The results revealed the presence of size-dependent two-photon absorption bands in the red and near-infrared spectral range. The cubic nonlinearity of core/shell CuInS2/ZnS quantum heterostructures is discussed in terms of both the CuInS2 core's optical transitions and the impact of the wide-gap ZnS shell layer. Kinetics of recombination of the single/two-photon excited states was investigated with femtosecond time-resolved photoluminescence spectroscopy revealing the complex character of electronic relaxation. A general statistical model involving normalized discrete distribution of decay rates was used for the analysis of luminescence decay curves. Different relaxation paths including the excitonic relaxation, donor–acceptor pair recombination and free-to-bound state recombination are discussed. The results indicate that optical properties of the CuInS2/ZnS and CuInS2 quantum dots are well suited for the steady-state as well as time-resolved single/multiphoton fluorescent techniques utilized commonly for the bio-sensing issues.

Nonlinear refraction and nonlinear absorption in stoichiometric colloidal CuInS2 quantum dots, with absorption edge tuned up to the visible spectral region, were investigated. The nonlinear optical response of the quantum dots was measured in a wide range of wavelengths (700–1600 nm) using the Z-scan technique. The measurements revealed the presence of two-photon absorption in the near-infrared range and the negative nonlinear refraction in almost whole spectral range for all the investigated nanoparticles. The cubic nonlinearity of CuInS2 quantum dots is discussed in terms of defect-related optical properties of the material. The results indicate that CuInS2 quantum dots may be an interesting material for the single and multiphoton luminescence bio-detection techniques.

We report the synthesis and physicochemical characterization of YVO4 nanocrystals doped with Eu3+ ions. The adopted solvothermal synthesis procedure rendered YVO4 nanoparticles with tetragonal crystal structure and rod-like morphology. The absorption and excitation spectra of the studied nanoparticles showed UV bands which were attributed to the 1A1 → 1T2 and 1A1 → 1T1 electronic transitions in the vanadate group, respectively. The nonlinear optical properties of both undoped YVO4 nanocrystals and those doped with Eu3+ ions were studied by wide wavelength range (600–1600 nm) femtosecond Z-scan measurements. The experiments revealed strong multiphoton absorption in the wavelengths around 650 and 1300 nm, within the first and second biological window. This nonlinear absorption results in multiphoton excitation of red europium emission from the nanoparticles, making them potential candidates for application as markers in nonlinear microscopy imaging techniques.