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A quasi-particle named plexciton emerges from the hybridization between plasmons and molecular excitons which exhibits characteristic spectral features, such as Fano resonance and Rabi splitting in extinction, scattering, and reflection spectroscopy. However, the understanding of the fluorescence properties in plexcitonic hybrids remains unclear, especially for nonlinear upconverted emissions. In this Letter, we prepared three-component plexcitonic hybrids with two cyanine dyes (Cy3 and Cy5) coupled to Ag nanostructured films and investigated their enhanced nonlinear radiation, including two-photon luminescence (TPL), second-harmonic generation (SHG), and surface-enhanced Raman scattering (SERS). The plexcitonic hybrids showed a splitting extinction spectrum with five peaks induced by the hybrid of the monomer and dimer excitons in the two cyanine dyes with surface plasmon resonance of the Ag films. Under the laser excitation at 1260 nm, the (Cy3–Cy5)/Ag hybrid had a 6.3-fold enhancement of TPL and a 5.1-fold enhancement of SHG compared to a two-component hybrid of Cy5/Ag. Our experimental results provide valuable insights for designing and manufacturing multicomponent plexcitonic devices with highly efficient nonlinear radiation. The plexcitonic hybrids, characterized by their featured extinction properties and largely enhanced upconverted emission, have great promise for applications in nonlinear optics, quantum information processing, biomedical sensing, and photochemistry. [ABSTRACT FROM AUTHOR]

Excitation of type IIb synthetic diamond by ultrashort laser pulses in the visible range causes broadband luminescence in the UV visible range; the observed luminescence band can be attributed to the A band characteristic of diamonds. The photoluminescence spectra were obtained at different laser pulse durations (0.3–6.2 ps) depending on the pulse energy. A nonlinear dependence of the luminescence yield on the intensity of ultrashort pulses is established. [ABSTRACT FROM AUTHOR]

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

We report the synthesis of plasmonic nanocapsules and the cellular responses they induce in 3D melanoma models for their perspective use as a photothermal therapeutic agent. The wall of the nanocapsules is composed of polyelectrolytes. The inner part is functionalized with discrete gold nanoislands. The cavity of the nanocapsules contains a fluorescent payload to show their ability for loading a cargo. The nanocapsules exhibit simultaneous two-photon luminescent, fluorescent properties and X-ray contrasting ability. The average fluorescence lifetime (τ) of the nanocapsules measured with FLIM (0.3 ns) is maintained regardless of the intracellular environment, thus proving their abilities for bioimaging of models such as 3D spheroids with a complex architecture. Their multimodal imaging properties are exploited for the first time to study tumorspheres cellular responses exposed to the nanocapsules. Specifically, we studied cellular uptake, toxicity, intracellular fate, generation of reactive oxygen species, and effect on the levels of hypoxia by using multi-photon and confocal laser scanning microscopy. Because of the high X-ray attenuation and atomic number of the gold nanostructure, we imaged the nanocapsule-cell interactions without processing the sample. We confirmed maintenance of the nanocapsules' geometry in the intracellular milieu with no impairment of the cellular ultrastructure. Furthermore, we observed the lack of cellular toxicity and no alteration in oxygen or reactive oxygen species levels. These results in 3D melanoma models contribute to the development of these nanocapsules for their exploitation in future applications as agents for imaging-guided photothermal therapy. The novelty of the work is that our plasmonic nanocapsules are multimodal. They are responsive to X-ray and to multiphoton and single-photon excitation. This allowed us to study their interaction with 2D and 3D cellular structures and specifically to obtain information on tumor cell parameters such as hypoxia, reactive oxygen species, and toxicity. These nanocapsules will be further validated as imaging-guided photothermal probes. [Display omitted] [ABSTRACT FROM AUTHOR]

Fabricating highly homogeneous plasmonic nanostructures over a large area and optically evaluating their structural quality are challenging. Here, we propose an elegant approach to achieve various dense nanoparticle arrays with tunable symmetries over centimeter-scale dimensions and optically evaluate the structural quality by spatially mapping nonlinear emissions from L-, U-, and O-shaped individual nanoparticles. In particular, the spectral overlapping of the second harmonic (SH) and two-photon luminescence (TPL) emissions is separated, and excitation polarization dependence and spatial fluctuations of the nonlinear signal across the nanostructures are investigated. Narrow Gaussian-distributed peaks in the intensity histogram of SH and TPL emissions confirm the high-level uniformity of the fabricated arrays. Distinct spatial distributions of SH and TPL emissions are observed, and their spatial correlation is very weak over large-area nanostructures. Furthermore, SH signals are demonstrated as a more sensitive indicator of the structural quality of nanoparticle arrays. Our findings not only offer an efficient way of constructing versatile large-scale nanostructures but also enable spatial nonlinear optics tailoring for applications of nano-optics and quantum information. [ABSTRACT FROM AUTHOR]

An endoplasmic reticulum (ER) targetable two-photon fluorescent probe termed ER-N3 is presented for the determination of hydrogen sulfide (H2S) in living cells and mice. The results demonstrate that ER-N3 was highly selective and sensitive to H2S. Confocal fluorescence imaging in living cells indicated that ER-N3 was accumulated in the endoplasmic reticulum and visualized exogenous and endogenous H2S production. Moreover, a burst of H2S upregulated by the nitric oxide donor sodium nitroprusside was monitored. Meanwhile, the increase of H2S ended following the addition of DL-propargylglycine, an inhibitor for cystathionine β-synthase and cystathionine γ-lyase that are the main sources of H2S. Importantly, the exogenous H2S was visualized in abdominal tissue of mice by utilizing two-photon fluorescence microscopy. The ER-N3 fluorescent probe may be an excellent tool to image H2S fluctuations in the endoplasmic reticulum and characterize the relationship between H2S and disease in vivo. [ABSTRACT FROM AUTHOR]

The dependencies of the average exciton luminescence power in ZnSe and ZnSe crystal samples doped with Fe 2+ on the average excitation radiation (ER) power during two-photon absorption of this radiation in the samples were investigated. The experimental dependence of the average luminescence power as a function of the average ER power at each point of this functional dependence was approximated by a power function. The index of power for the ZnSe:Fe 2 + sample was close to 4 over the entire range of ER power, while in the ZnSe crystal without doping this the index of power depended on the ER power and decreased from 4.5 to 2.2 with increasing ER power. The obtained results are explained by the fact that the value of the index of power depends on the density of energy levels in the band gap associated with impuritydefect centers (IDC) in the samples, and the difference in the behavior of the index of power with the different power of ER in them is explained by a higher concentration of IDC in sample doped with iron compared to undoped. The simulation to support this point of view are provided. The results point to the possibility of assessing the quality of semiconductor crystals in terms of IDC density by the dependence of exciton twophoton luminescence power on the power of the ER upon its two-photon absorption. • ZnSe and ZnSe:Fe single crystals were investigated. The initial undoped samples were made by free-growth method on a single-crystal ZnSe substrate. Iron doping was carried out by the diffusion method. • The dependence of exciton two-photon luminescence power on the excitation power (P l u m ∼ P e x n) in ZnSe and ZnSe:Fe was studied. The n (index of power) is between 4 and 5 in the whole range of excitation radiation powers in the ZnSe:Fe2+ sample, and is close to 2 at high excitation power in ZnSe. • The proposed technique can be a basis for a method to quantify the quality of semiconductor samples in terms of the density of all recombination-active impurity-defective centers. [ABSTRACT FROM AUTHOR]

The results of a study of multiphoton-excited luminescence and Stimulated Raman scattering (SRS) of POPOP in a form of crystalline powder and toluene solution are presented. Two-photon and three-photon-excited luminescence in POPOP crystalline powder and toluene solution was registered under excitation by pico- and nanosecond laser pulses. Samples cooling to the temperature of liquid nitrogen leads to the appearance of an additional line in the luminescence spectrum at a wavelength of 447 nm, SRS lines intensity increasing accompanying two-photon luminescence process and changing temporal dynamics, a decrease in the contribution of the fast component in the decay time curve. • The effect of multiphoton absorption on the POPOP luminescence properties. • More efficient multiphoton luminescence for inhomogeneous form. • An additional line in luminescence spectrum of crystalline POPOP at low temperature. • The fast time component decreasing at low temperature. • The threshold nature of the SRS energy dependence accompanying TPL. [ABSTRACT FROM AUTHOR]

Two-photon luminescence with near-infrared (NIR) excitation of upconversion nanoparticles (NPs) is of great importance in biological imaging due to deep penetration in high-scattering tissues, low auto-luminescence and good sectioning ability. Unfortunately, common two-photon luminescence is in visible band with an extremely high exciation power density, which limits its application. Here, we synthesized NaYF4:Yb/Tm@NaYF4 upconversion NPs with strong two-photon NIR emission and a low excitation power density. Furthermore, NaYF4:Yb/Tm@NaYF4@SiO2@OTMS@F127 NPs with high chemical stability were obtained by a modified multilayer coating method which was applied to upconversion NPs for the first time. In addition, it is shown that the as-prepared hydrophillic upconversion NPs have great biocompatibility and kept stable for 6 hours during in vivo whole-body imaging. The vessels with two-photon luminescence were clear even under an excitation power density as low as 25mW/cm2. Vivid visualizations of capillaries and vessels in a mouse brain were also obtained with low background and high contrast. Because of cheaper instruments and safer power density, the NIR two-photon luminescence of NaYF4:Yb/Tm@NaYF4 upconversion NPs could promote wider application of two-photon technology. The modified multilayer coating method could be widely used for upconversion NPs to increase the stable time of the in vivo circulation. Our work possesses a great potential for deep imaging and imaging-guided treatment in the future.

Two-photon luminescence with near-infrared (NIR) excitation of upconversion nanoparticles (NPs) is of great importance in biological imaging due to deep penetration in high-scattering tissues, low auto-luminescence and good sectioning ability. Unfortunately, common two-photon luminescence is in visible band with an extremely high exciation power density, which limits its application. Here, we synthesized NaYF4:Yb / Tm@NaYF4 upconversion NPs with strong two-photon NIR emission and a low excitation power density. Furthermore, NaYF4:Yb / Tm@NaYF4@SiO2@OTMS@F127 NPs with high chemical stability were obtained by a modified multilayer coating method which was applied to upconversion NPs for the first time. In addition, it is shown that the as-prepared hydrophillic upconversion NPs have great biocompatibility and kept stable for 6 hours during in vivo whole-body imaging. The vessels with two-photon luminescence were clear even under an excitation power density as low as 25 mW / cm2. Vivid visualizations of capillaries and vessels in a mouse brain were also obtained with low background and high contrast. Because of cheaper instruments and safer power density, the NIR two-photon luminescence of NaYF4:Yb / Tm@NaYF4 upconversion NPs could promote wider application of two-photon technology. The modified multilayer coating method could be widely used for upconversion NPs to increase the stable time of the in vivo circulation. Our work possesses a great potential for deep imaging and imaging-guided treatment in the future. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract By "seeing" the green two-photon luminescence, two separate focusing points are observed on the propagation axis of a converging femtosecond laser beam in a ZnO single crystal rod. It is found that the self-focusing effect makes a significant contribution to the formation of the first focusing point, while the second focusing point is caused by self-refocusing. The position of the first focusing point is in good agreement with the value predicted by a model developed by Chin and his co-workers. These experimental findings could be the unprecedented evidence for the self-focusing and refocusing effect of the femtosecond laser filament propagation in nonlinear media. [ABSTRACT FROM AUTHOR]

Abstract: A two‐photon pumped non‐linear optical (NLO) Fabry‐Pèrot (F‐P) type organic micro‐crystal resonator useful for a myriad of upconversion‐based light technologies is presented. The resonator is parallelepiped‐shaped and composed of a self‐assembled donor‐acceptor‐donor type molecule namely, 9,9,9”,9”‐tetramethyl‐9H,9’H,9”H‐[2, 2’:7,2”‐terfluoren]‐9’‐one (TTO). X‐ray crystal structure of an orange‐yellow TTO micro‐crystal reveals C−H⋅⋅⋅O type weak intermolecular hydrogen bond between the oxygen atom of the fluorenone unit and fluorine hydrogen atom. For one‐ and two‐photon excitation the micro‐crystals exhibit F‐P type modes in their photoluminescence signal. The fundamental frequency‐dependent NLO intensity shows a continuous increase as the fundamental wavelength is decreasing down to 770 nm. The two‐photon luminescence signals from these micro‐resonators are several orders of magnitude higher than the thin films of similar thickness. [ABSTRACT FROM AUTHOR]

Micron-sized gold plates were prepared by reducing chloroauric acid with lemongrass extract. Their two-photon luminescence (TPL) and second harmonic generation (SHG) were investigated. The results show that the TPL and SHG intensity of gold plates is dependent on the wavelength and polarization of excitation laser. The TPL intensity of gold plates decreases with the increase of the excitation wavelength except for a small peak around 820–840 nm, while SHG intensity increases with the excitation wavelength redshift. In addition, it is found that the TPL intensity of the gold plate’s edge is related with the angle between the edge orientation and the polarization direction of the excitation light. The TPL intensity increases with the angle increase from 0° to 90°.

Optical nanoantennas have shown their great potential for far-field to near-field coupling and for light confinement in subwavelength volumes. Here, we report on a multimodal configuration for bright and polarization-dependent bowtie antenna based on large and highly crystalline gold prisms. Each individual prism constituting an antenna arm sustains high order plasmon modes in the visible and near infrared range that allow for high field confinement and two-dimensional optical information propagation. We demonstrate by scanning two-photon luminescence (TPL) microscopy and numerical simulations based on the Green dyadic method that these bowtie antennas result in intense hot spots in different antenna locations as a function of the incident polarization. Finally, we quantify the local field enhancement above the antennas by computing the normalized total decay rate of a molecular system placed in the near field of the antenna gap as a function of the dipole orientation. We demonstrate the existence of a subtle relation between antenna geometry, polarization dependence and field enhancement. These new multimodal optical antennas are excellent far field to near field converter and they open the door for new strategies in the design of coplanar optical components for a wide range of applications including sensing, energy conversion or integrated information processing. [ABSTRACT FROM AUTHOR]

Typical lead-based halide perovskite has been extensively explored as a light-harvesting and emission material for solar cell and light-emitting diodes in the past ten years. But it remains challenging to improve the optoelectronic characteristics and clarify the photophysical mechanism with the interaction of laser. Herein, the nonlinear optical absorption and two-photon luminescent properties of FAPbBr 3 (FA=CH(NH 2) 2 +) nanocrystals (NCs) are investigated by means of open-aperture Z-scan, steady-state/time-resolved photoluminescence (PL), and transient absorption (TA) techniques. When the laser excitation wavelength varies from 475 to 532 nm in open-aperture Z-scan measurement, strong saturated absorption can be found and its saturation intensity increases. Compared with normal luminescence, the PL emission peak has a red shift of 6 nm and increased PL lifetime under 800 nm femtosecond laser excitation, and the linewidth changes smaller considerably from 114 to 94 meV. This difference is mainly attributed to the different relaxation pathways. The TA spectra show the PL peak positions and full width at half maximum different features under 400 or 800 nm femtosecond excitation on the time scale. Due to different selection rules, the 400 or 800 nm femtosecond excitations can induce electrons populated different states and then relax to the same lowest excited state. Hence, we can estimate that different states induce the difference in steady-state PL, TRPL, and TA decays. These results may contribute to the application of perovskite NCs for multifunctional photonic sources and nanolaser devices under strong laser field. [Display omitted] • The nonlinear optical properties of FAPbBr 3 NCs are investigated using the open-hole Z-scan technique. • Different relaxation pathways are found to explain the red shift of the PL emission peak. • The time-resolved PL and transient absorption spectra show the coexistence of excitonic and trapping states. [ABSTRACT FROM AUTHOR]

Gold nanostars (GNS) have been coated with four different polyethylene glycols (PEGs) equipped with a –SH function for grafting on the gold surface. These PEGs have different chain lengths with average MW = 2000, 3000, 5000 and average number of –O–CH 2 –CH 2 — units 44, 66, and 111, respectively. Two are neutral and two are terminated with –COOH and –NH 2 functions, thus bearing negative and positive charges at physiological pH, thanks to the formation of carboxylate and ammonium groups. The negative charge of the GNS coated with PEG carboxylate has also been exploited to further coat the GNS with the PAH (polyallylamine hydrochloride) cationic polymer. Vitality tests have been carried out on SH-SY5Y cells treated with the five differently coated GNS for 4, 24, and 48 h, at Au concentrations ranging from 1.25 to 100 μg/mL. The same tests have been repeated with the pure PEGs and PAH. Excellent biocompatibility was found for all PEGs, independently on charge and chain length, both for coated GNS and for the pure polymers. On the contrary, poor biocompatibility was found for PAH overcoated GNS and for pure PAH, although the latter only at high concentrations. Exploiting the two-photon luminescence of GNS, we have found by confocal laser scanning microscopy that when GNS are coated with PEGs they do not enter SH-SY5Y cells, while when overcoated with PAH they massively penetrate into the cytoplasm. This causes cell death by dramatically changing cell morphology, as demonstrated also by atomic force microscopy. [ABSTRACT FROM AUTHOR]

The design and development of functional hybrid nanomaterials is currently a topic of great interest in biomedicine. Herein we investigated the grafting of Ru(II) polypyridyl complexes onto gold nanospheres (Ru@AuNPs) to improve the particles' near infrared (NIR) absorption, and ultimately allow for application in photothermal cancer therapy. As demonstrated in this article, these ruthenium(II) complexes could indeed significantly enhance gold nanospheres' two-photon luminescence (PTL) intensity and photothermal therapy (PTT) efficiency. The best dual functional nanoparticles of this study were successfully used for real-time luminescent imaging-guided PTT in live cancer cells. Furthermore, in vivo tumor ablation was achieved with excellent treatment efficacy under a diode laser (808 nm) irradiation at the power density of 0.8 W/cm 2 for 5 min. This study demonstrates that the coupling of inert Ru(II) polypyridyl complexes to gold nanospheres allows for the enhancement of two-photon luminescence and for efficient photothermal effect. [ABSTRACT FROM AUTHOR]

Fluorescence detection is the most effective tool for tracking gene delivery in living cells. To reduce photodamage and autofluorescence and to increase deep penetration into cells, choosing appropriate fluorophores that are capable of two-photon activation under irradiation in the NIR or IR regions is an effective approach. In this work, we have developed six tetranuclear ruthenium(II) complexes, GV1-6, and have studied their one- and two-photon luminescence properties. DNA interaction studies have demonstrated that GV2-6, bearing hydrophobic alkyl ether chains, show more efficient DNA condensing ability but lower DNA binding constants than GV1. However, the hydrophobic alkyl ether chains also enhance the DNA delivery ability of GV2-6 compared with that of GV1. More importantly, we have applied GV1-6 as non-viral gene vectors for tracking DNA delivery in living cells by one- and two-photon fluorescence microscopies. In two-photon microscopy, a high signal-to-noise contrast was achieved by irradiation with an 830 nm laser. This is the first example of the use of transition-metal complexes for two-photon luminescent tracking of the cellular pathways of gene delivery and as DNA carriers. Our work provides new insights into improving real-time tracking during gene delivery and transfection as well as important information for the design of multifunctional non-viral vectors. [ABSTRACT FROM AUTHOR]

Near-infrared (NIR) light-mediated two-photon microscopy has become a promising tool for early cancer therapy. However, exploring novel two-photon probe with high biocompatibility and high photostability to resist photobleaching, remains a key challenge for performing in vivo bioimaging. Herein, a novel two-photon luminescence (TPL) probe named two-dimensional rhenium disulfide (ReS 2) nanosheets was firstly reported for performing intracellular bioimaging. Under the illumination of low power NIR femtosecond laser, the prepared ReS 2 nanosheets exhibited strong NIR photon absorption, generating a strong TPL band at 640 nm. In addition, in vitro TPL imaging showed that, ReS 2 nanosheets possessed excellent photostability, enabling to resist photobleaching. More importantly, ReS 2 nanosheets functionalized by polyethylene glycol (PEG) showed negligible cytotoxicity, suitable to perform intracellular TPL imaging. With prolonged 6-hour incubation time, the TPL intensity of PEG-ReS 2 nanosheets in three kinds of living cells such as esophageal cancer cells (KYSE150), pancreatic cancer cells (4T1) and HeLa cells, were significantly enhanced by almost 4, 11, and 17 times, respectively. In view of their photothermal effects, the PEG-ReS 2 nanosheets could work as an excellent TPL probe for monitoring photothermal therapy and evaluating therapeutic outcomes. This study highlights great potential of PEG-ReS 2 nanosheets as a TPL biosensor for intracellular optical imaging and cancer therapy. • A novel TPL nanoprobe named 2D rhenium disulfide (ReS 2) nanosheets was prepared. • The proposed probe showed excellent photostability, enabling to resist photobleaching. • The proposed probe exhibited negligible cytotoxicity, enabling to perform in vivo bioimaging. [ABSTRACT FROM AUTHOR]

Facile and accurate temperature measurement is crucial in daily life, industrial applications, and scientific research. Here, we present a new strategy for physiological temperature sensing based on dual-emission from second harmonic generation (SHG) signal and two-photon luminescence in a dye-loaded nonlinear metal-organic framework (MOF) composite FIR-8⊃DMASM (DMASM = 4-[p-(dimethylamino)styryl]-1-methylpyridinium). Powder X-ray diffraction (PXRD), thermal gravimetric analysis (TGA), infrared absorption spectrum, single-photon luminescence, and the quantum yield indicate that encapsulation not only provides a two-photon luminescence center, but also improves the stability and quantum efficiency of dyes. Temperature-dependent spectroscopy shows that FIR-8⊃DMASM has excellent sensory performance in the physiological temperature region (20–60 °C) with high relative sensitivity of 1.36–2.98% oC−1. With good water stability and excellent biocompatibility, FIR-8⊃DMASM can be potentially applied in biological temperature sensing. A dye-loaded metal-organic framework FIR-8⊃DMASM shows excellent self-calibrated physiological temperature sensing performance with high relative sensitivity of 1.36–2.98% oC−1, good water stability, and excellent biocompatibility. [Display omitted] • Physiological thermometer based on dual-emitting MOF⊃dye composite has been realized. • Two signals for sensing are SHG and two-photon luminescence in MOF⊃dye composite. • FIR-8⊃DMASM exhibits high relative sensitivity, good repeatability, water stability and biocompatibility. [ABSTRACT FROM AUTHOR]

Utilizing three-dimensional vectorial electromagnetic simulation, we propose a new refractive index sensing mechanism based on Fano resonance enhanced two-photon-absorption induced luminescence (TPL). The TPL from gold nanodisk heptamer (GNDH), which is affected by the refractive index of surrounding material, is used as an example to demonstrate the sensing mechanism facilitated by Fano resonance. The sensitivity of our method is about one order of magnitude better than the conventional refractive index sensing strategy employing plasmonic Fano resonance, while the size of the sensing probe can be further reduced at the same time. [ABSTRACT FROM AUTHOR]

We report that a nanoporous Au film capped with a dielectric surface layer enables the effective absorption of near-infrared light and intense emission of two-photon luminescence. In this approach, nanoscale pores in Au are incorporated by chemical dissolution and microscale surface patterns are added on the nanoporous Au by microcontact print lithography. Electromagnetic simulation shows that the strong local electric fields are concentrated in the vicinity of nanopores in the Au film and are further increased by the surface dielectric patterns, which leads to a 40-fold increase in the intensity of the two-photon luminescence, as verified by photoemission measurement. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Anapole states associated with the destructive interference between dipole and toroidal moments result in suppressed scattering accompanied by strongly enhanced near fields. In this work, we comprehensively examine the anapole state formation in metal-insulator-metal configurations supporting gap surface-plasmon (GSP) resonances that are widely used in plasmonics. Using multipole decomposition, we show that in contrast to the common case of dielectric particles with out-of-phase superposition of electric and toroidal dipoles anapole states in GSP resonators are formed due to the compensation of magnetic dipole moments. Unlike anapole states in dielectric particles, magnetic anapole states in GSP resonator does not provide a pronounced suppression of scattering, but it features huge electric field enhancement, which we verify by numerical simulations and two-photon luminescence measurements. This makes the GSP resonator configuration very promising for use in a wide range of applications, ranging from nonlinear harmonic generation to absorption enhancement and sensing.

Abstract: In this work we report on the ability of Er/Yb co-doped NaYF4 nano-crystals and CdTe Quantum Dots as two-photon excited fluorescent nano-thermometers. The basic physical phenomena causing the thermal sensitivity of the two-photon excited emission bands have been discussed and the maximum thermal resolution achievable in each case has been estimated. The practical application of both systems for thermal sensing at the micro-scale in biological systems is demonstrated. In particular, they have been used to evaluate the thermal loading induced by tightly focused laser beams in both living cells and fluids. [Copyright &y& Elsevier]

Using a spray-drying process, we developed a versatile, one step synthesis, of two-photon luminescent silicate nanoparticles. The formation of the nanoparticles is based on the controlled drying of sol-gel droplets in a heated laminar flux inside a tubular furnace. Two types of nanoparticles were prepared, hybrid core-shell nanoparticles and silicate nanoparticles doped with an europium(III) complex. In the first case of hybrid (organic-silicate) coreshell nanoparticles the last evaporation of THF solvent enhance the polycondensation of the silicate network in the droplets, particularly at their surface. This induces first the formation of a silicate crust followed, at the end of the solvent evaporation, by the nucleation and growth of the organic dye in the core of the resulting dried nanoparticles. We studied the different physical and chemical parameters that influence the perfect and reproducible control of the confined nucleation and growth of dye nanocrystals in the sol-gel droplets. In the second case, silicate nanoparticles were doped with a functionalized tris-dipicolinate europium complex, which presents an important two-photon absorption cross section but exhibits a weak stability in water due to the dissociation of the complex. Two different compositions of the starting sols were tested to adjust the hydrophilic character of the nanoparticles and to avoid the dissociation of the europium complexes in water by closing the porosity of the silicate shell. [ABSTRACT FROM AUTHOR]

Abstract: Two-photon-excited luminescence after femtosecond near-infrared (NIR) excitation was observed in chemically oxidized silicon nanocrystals (Si-nc) produced by laser-assisted pyrolysis of silane. The luminescence time decay and emission spectrum resulted in good agreement with those after blue excitation. The underlying two-photon absorption coefficient was also measured by the open-aperture z-scan technique, obtaining a value of 12.5cm/GW, which is intermediate between the values reported in the literature for bulk silicon and for very small Si-nc. [Copyright &y& Elsevier]

Recent years have seen tremendous progress in the design and study of nanomaterials geared towards biological and biomedical applications, most notable among these being the noble metal nanoparticles. In this review, we outline the surface-plasmon resonance-enhanced optical properties of colloidal gold nanoparticles directed towards recent biomedical applications with an emphasis on cancer diagnostics and therapeutics. Methods of molecular-specific diagnostics/detection of cancer, including strongly enhanced surface plasmon resonance light-scattering, surface-enhanced emission of gold nanorods and surface-enhanced Raman scattering, are described. We also discuss the plasmonic photothermal therapy of cancer achieved by using the strongly enhanced surface-plasmon resonance absorption of gold nanospheres and nanorods. [ABSTRACT FROM AUTHOR]

Abstract: Two-photon processes are used for studying photoinduced phase transition (PIPT) from diamagnetic low-temperature phase to paramagnetic high-temperature phase in strongly correlated organic radical 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA) crystals. We have measured the Raman and luminescence spectra in the low-temperature phase after two-photon excitation with various excitation photon densities. After correction of re-absorption of the luminescence, the shape of the two-photon luminescence spectrum is in good agreement with that of the one-photon luminescence spectrum, which strongly suggests that the initial states of the two-photon luminescence are the same as those of the one-photon luminescence and are self-trapped excitons (STEs). As increasing the excitation photon density, PIPT to the high-temperature phase takes place with a threshold behavior as a sudden decrease of the two-photon luminescence intensity. This result suggests that STEs are the precursors of the PIPT and the two-photon luminescence can be a useful probe of whole PIPT dynamics from the microscopic lattice distortion to the macroscopic phase transition. [Copyright &y& Elsevier]

Abstract: We report the two-photon luminescence (TPL) and second-harmonic generation (SHG) characteristics of zinc oxide (ZnO) in ceramic, thick film and nanorod. Sintering, physical vapour deposition (PVD), and hydrothermal methods were used in preparing the three forms of samples, respectively. Wide-band luminescence in the visible wavelength was observed with green/yellow emission in ceramic and nano-crystal, and blue emission in the film. We attributed interstitial zinc and interstitial oxygen for the luminescence at blue and green bands. Images acquired by TPL and SHG microscopy are presented, interpretation is provided for granular structure exhibiting strong SHG at granular boundaries. [Copyright &y& Elsevier]

Presenting a safe alternative to conventional compound quantum dots and other functional nanostructures, nanosilicon can offer a series of breakthrough hyperthermia‐based therapies under near‐infrared, radiofrequency, ultrasound, etc., excitation, but the size range to sensitize these therapies is typically too large (>10 nm) to enable efficient imaging functionality based on photoluminescence properties of quantum‐confined excitonic states. Here, it is shown that large Si nanoparticles (NPs) are capable of providing two‐photon excited luminescence (TPEL) and second harmonic generation (SHG) responses, much exceeding that of smaller Si NPs, which promises their use as probes for bi‐modal nonlinear optical bioimaging. It is finally demonstrated that the combination of TPEL and SHG channels makes possible efficient tracing of both separated Si NPs and their aggregations in different cell compartments, while the resolution of such an approach is enough to obtain 3D images. The obtained bi‐modal contrast provides lacking imaging functionality for large Si NPs and promises the development of novel cancer theranostic modalities on their basis. [ABSTRACT FROM AUTHOR]

Transition metal chalcogenides are investigated for catalyst, intermediary agency, and particular optical properties because of their distinguished electron-vacancy-transfer (EVT) process toward different applications. In this work, one convenient approach for making pure-phased FeSe nanocrystals (NCs) and doped CuFeSe nanosheets (NSs) through a wet chemistry method in mixed solvents is illustrated. The surface modification of each product is realized by using a peptide molecule glutathione (GSH), in which the thiol group (-SH) is ascribed to be the in situ reducer and bonding agency between the crystalline surface and surfactant in whole constructing processes. Due to the functional groups in biological GSH, highly aggregated NCs are rebuilt in the form of an FeSe hollow structure through amino and carboxyl cross-linking functions through a spontaneous assembly procedure. Owing to the coupling procedure of Cu and Fe in the growth process, it generates enhanced EVT. Additionally, it shows the emission spectra of λ EM-PL = 436 nm (FeSe) and 452 nm (CuFeSe) while λ EX-PL = 356 nm, it also conveys two-photon phenomenon while λ EX-PL = 720 nm. Moreover, it also shows strong off-resonant luminescence due to two-photon absorption, which should be valuable for biological applications., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The strong light-matter interaction in monolayer transition metal dichalcogenides (TMDs) is promising for nanoscale optoelectronics with their direct band gap nature and the ultrafast radiative decay of the strongly bound excitons these materials host. However, the impeded amount of light absorption imposed by the ultrathin nature of the monolayers impairs their viability in photonic applications. Using a layered heterostructure of a monolayer TMD stacked on top of strongly absorbing, nonluminescent, multilayer SnSe 2 , we show that both single-photon and two-photon luminescence from the TMD monolayer can be enhanced by a factor of 14 and 7.5, respectively. This is enabled through interlayer dipole-dipole coupling induced nonradiative Förster resonance energy transfer (FRET) from SnSe 2 underneath, which acts as a scavenger of the light unabsorbed by the monolayer TMD. The design strategy exploits the near-resonance between the direct energy gap of SnSe 2 and the excitonic gap of monolayer TMD, the smallest possible separation between donor and acceptor facilitated by van der Waals heterojunction, and the in-plane orientation of dipoles in these layered materials. The FRET-driven uniform single- and two-photon luminescence enhancement over the entire junction area is advantageous over the local enhancement in quantum dot or plasmonic structure integrated 2D layers and is promising for improving quantum efficiency in imaging, optoelectronic, and photonic applications.

Carbon dots (CDs) have gained intensive interests owing to their unique structure and excellent optoelectronic performances. However, to acquire CDs with a broadband emission spectrum still remains an issue. In this work, nitrogen-doped CDs (N-CDs) with near-ultraviolet (NUV), visible, and near-infrared (NIR) emission were synthesized via one-pot solvothermal strategy, and the excitation-independent NUV and NIR emission and excitation-dependent visible emission were observed in the photoluminescence (PL) spectra of N-CDs. Moreover, the as-synthesized N-CDs displayed two-photon fluorescence emission. It is important to note that N-CDs also exhibited piezochromic luminescence with reversibility, in which the red- and blue-shifted PL with increasing applied pressure (0.07-5.18 GPa) and the red- and blue-shifted PL with releasing applied pressure (5.18 GPa to 1 atm) were developed for the first time. Combined with good hydrophilicity, high photobleaching resistance, and low toxicity, the piezochromic luminescence would greatly boost the valuable applications of N-CDs.