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Nanotechnology is considered as an emerging effective means to augment plant photosynthesis. However, there is still a lot of work to be done in this field. Here, we applied the upconversion nanoparticles (UCNPs) on lettuce leaves and found that the UCNPs were able to transport into the lettuce body and colocalize with the chloroplasts. It was proved that UCNPs could harvest the near-infrared light of sunlight and increase the electron transfer rate in the photosynthesis process, thus increasing the photosynthesis rate. The gene expression analysis showed that more than 90% of gene expression in photosynthesis was upregulated. After spraying the UCNP solution on the leaves of lettuce and placing the lettuce under sunlight for 1 week, the wet/dry weight of the leaves increased by 53.33% and 45.71%, respectively. This nanoengineering of light-harvesting UCNPs may have great potential for applications in agriculture.

The structure of the host lattice has a substantial influence on the optical properties of lanthanide-doped luminescent materials. Hexagonal-phase (β-phase) NaREF4 (RE = rare earth) is the most commonly used crystal structure for lanthanide-doped upconversion nanoparticles (UCNPs) owing to its high upconversion (UC) efficiency. In this work, we report, for the first time, that more efficient cooperative sensitization upconversion (CSU) can be achieved in cubic-phase (α-phase) NaREF4 UCNPs instead of their β-phase counterparts. With the passivation of an inert shell, the UC emission intensity of α-NaYbF4:Tb40%@CaF2 is 10.5 times higher than that of β-NaYbF4:Tb40%@NaYF4. We propose that the high-symmetry crystal structure of the α phase facilitates the formations of [Yb–Yb] dimers and [Yb–Yb–Tb] clusters, which are particularly beneficial for CSU. Moreover, we prove that such Tb3+-based UCNPs are almost impervious to water quenching because of the large energy gap (∼15,000 cm−1) that existed in Tb3+ between its lowest emit-ting level (5D4) and next low-lying level (7F0). Finally, their potential application for single-nanoparticle imaging has also been demonstrated. As expected, the α-core-shell UCNPs measured at the single-nanoparticle level are estimated to be 9-fold brighter than their β-core-shell counterparts. Importantly, the α-NaYbF4:Tb40%@CaF2 UCNPs offer exciting opportunities for realizing single-nanoparticle imaging at ultralow irradiance (30 W/cm2).

One-dimensional (1D) metal halide perovskite nanowire (NW) arrays with high absorption efficiency, emission yield and dielectric constants, as well as anisotropic optoelectronic properties have found applications in energy harvesting, flexible electronics, and biomedical imaging devices. Here, a modified two-step solvothermal method is developed for the synthesis of self-assembled cubic CsPbBr3 NW arrays. This method provides facile access to continuous and uniform ultrafine perovskite NWs and well-aligned pure perovskite NW arrayed architectures. Under excitation at 365 nm, the CsPbBr3 NWs give a strong blue emission observable to the naked eyes. The CsPbBr3 NWs also exhibit strong two-photon excited luminescence under the irradiation with an 800 nm pulse laser. By rotating the polarization angle of the 800 nm laser, strong polarization dependence with a polarization degree up to ∼0.49 is demonstrated in the self-assembled CsPbBr3 NW array, although the CsPbBr3 NWs have an isotropic cubic structure. Based on density functional theory (DFT) calculations, this polarization-dependent emission is correlated with the anisotropic charge density distribution of the perovskite NWs. These findings suggest that the ultrafine CsPbBr3 NWs with a well-defined self-assembled architecture could be applied as next-generation polarization-sensitive photoelectronic detection materials.

Plant cell imaging is critical for agricultural production and plant pathology study. Advanced upconversion nanoparticles (UCNPs) are being developed as fluorescent probes for imaging cells and tissues in vivo and in vitro. Unfortunately, the thick cellulosic walls as barriers together with hemicelluloses and pectin hinder the entrance of macromolecules into the epidermal plant cell. Hence, realizing satisfactory temporal and spatial resolution with UCNPs remains an arduous task. Here, bipyramidal LiErF4:1%Tm3+@LiYF4 core–shell UCNPs with a super-bright red emission upon 980 nm laser excitation are explored, where the introduction of Tm3+ ions permits alleviation of the energy loss at defective sites and a significant improvement of the upconversion output. The as-obtained bipyramidal UCNPs could readily puncture plant cell walls and further penetrate into cell membranes, facilitating improved tissue imaging of cellular internalization, as demonstrated with the luminescence images obtained by multiphoton laser-scanning microscopy. Hence our work opens up a new avenue for exploring effective upconversion nanoparticles for achieving high resolution imaging of plant tissues.

Stimulated emission depletion (STED) microscopy is a powerful diffraction-unlimited technique for fluorescence imaging. Despite its rapid evolution, STED fundamentally suffers from high-intensity light illumination, sophisticated probe-defined laser schemes, and limited photon budget of the probes. Here, we demonstrate a versatile strategy, stimulated-emission induced excitation depletion (STExD), to deplete the emission of multi-chromatic probes using a single pair of low-power, near-infrared (NIR), continuous-wave (CW) lasers with fixed wavelengths. With the effect of cascade amplified depletion in lanthanide upconversion systems, we achieve emission inhibition for a wide range of emitters (e.g., Nd3+, Yb3+, Er3+, Ho3+, Pr3+, Eu3+, Tm3+, Gd3+, and Tb3+) by manipulating their common sensitizer, i.e., Nd3+ ions, using a 1064-nm laser. With NaYF4:Nd nanoparticles, we demonstrate an ultrahigh depletion efficiency of 99.3 ± 0.3% for the 450 nm emission with a low saturation intensity of 23.8 ± 0.4 kW cm−2. We further demonstrate nanoscopic imaging with a series of multi-chromatic nanoprobes with a lateral resolution down to 34 nm, two-color STExD imaging, and subcellular imaging of the immunolabelled actin filaments. The strategy expounded here promotes single wavelength-pair nanoscopy for multi-chromatic probes and for multi-color imaging under low-intensity-level NIR-II CW laser depletion.

Nonlinear depletion of fluorescence states by stimulated emission constitutes the basis of far-field stimulated emission depletion (STED) microscopy1,2. Despite significant efforts over the past decade, achieving resolution below the diffraction limit at low saturation intensities by STED remains a major technical challenge3,4. By taking advantage of the surface quenching effect in NaGdF4:Yb/Tm nanocrystals, we report here high-efficiency emission depletion through nanocrystal surface migration. Under a dual-beam, continuous-wave, laser manipulation (975-nm excitation and 730-nm de-excitation), we achieved an emission depletion efficiency of over 95% and a depletion saturation intensity of 18.3 kW cm-2. Emission depletion by surface migration through Gd sublattices enables super-resolution microscopic imaging with an average lateral resolution of 20 nm and a Fourier ring correlation (FRC) resolution of 24-32 nm (depletion beam intensity, 1.09 MW cm-2). Our approach circumvents the fundamental limitation of high-intensity STED microscopy, providing autofluorescence-free, re-excitation-background-free imaging with a depletion saturation intensity over three orders of magnitude lower than conventional fluorophores. We also demonstrated super-resolution imaging of actin filaments of fixed Hela cells labelled with 8-nm Tm3+-activated nanoparticles. Combined with the outstanding photostability of lanthanide luminescence, surface migration emission depletion could provide a powerful mechanism for low-power, super-resolution imaging or tracking of biological dynamics without photobleaching.

In recent years, the application of nanomaterials in promoting plant growth and augmenting photosynthesis has aroused great interest. Herein, carbon dots (CDs) are combined with NaYF4:Yb,Er to achi...

The use of bioorthogonal fluorogenic probes is superior to labelling and imaging of biomolecules in live cells and organisms, although overcoming the limitation of autofluorescence is still a challenge for current probes to achieve high illumination resolution of the target of interest. We herein demonstrate a functionalized terbium complex Tb-1 that is stable and biocompatible to enable bioorthogonal ligation with engineered cell-surface glycans for providing responsive luminescence. A luminescence resonance energy transfer (LRET) quencher with bioorthogonal properties is strategically incorporated into a tripodal terbium complex with low toxicity, which can undergo a click-cycloaddition reaction with a cyclooctene to completely change the electronic structure of the quencher, resulting in a much less efficient LRET but a 5-fold enhancement in the long-lived terbium emission intensity. This work therefore establishes a time-resolved platform that enables labelling and imaging of the biomolecules of interest.

Acquired brain injury (ABI), which is the umbrella term for all brain injuries, is one of the most dangerous diseases resulting in high morbidity and mortality, making it extremely significant to early diagnosis of ABI. Current methods, which are mainly composed of X-ray computed tomography and magnetic resonance angiography, remain limited in diagnosis of ABI with respect to limited spatial resolution and long scanning times. Here, we reported through-skull fluorescence imaging of mouse cerebral vasculature without craniotomy, utilizing the fluorescence of down-conversion nanoparticles (DCNPs) in the 1.3 - 1.7 μm near-infrared window (NIR-II window). Due to its high spatial resolution of 22.79 μm, the NIR-II fluorescence imaging method could quickly distinguish the brain injury region of mice after performing the stab wound injury (traumatic brain injury) and ischemic stroke (non-traumatic brain injury), enabling it a powerful tool in the noninvasive and early diagnosis of ABI.

In this study, flavonoid myricetin-mediated gold nanoparticles (Myr-AuNPs) were synthesized and their molecular interactions were evaluated through a combined experimental and theoretical study. The physicochemical properties of the synthesized Myr-AuNPs were characterized using TEM, FT-IR, and XRD analysis. The average particle size of the Myr-AuNPs was found to be 6 nm with spherical in shape. FT-IR results indicated that the hydroxyl groups of myricetin interacts with Au 3+ ions during the nanoparticles formation. Consequently, density functional theory (DFT) was used to evaluate the possible molecular interactions of myricetin hydroxyl groups with Au 3+ ions. Interestingly, the DFT results confirmed that the 5′-hydroxyl group of ring B in myricetin was more suitable and highly stable to interact with Au 3+ ions during the nanoparticles formation in aqueous medium. Further, this study emphasized that the synthesized Myr-AuNPs exhibits excellent pH, temperature, and storage stability. In addition to this, biocompatibility study recommended that Myr-AuNPs is safe for therapeutic applications. This is the first detailed report on the molecular interaction between the hydroxyl groups of myricetin and Au 3+ ions during the nanoparticle formation.

Improvement of the facile synthesis strategy is an effective way to tune the optical properties of lanthanide-doped upconversion nanoparticles. However, it is necessary to directly study the growth...

The lead sulfide (PbS) thin films with Zn doping concentration from 0 at.% to 5 at.% were synthesized utilizing chemical bath deposition technique. X-ray diffraction (XRD) revealed that the calculated crystallite size decreased from 20.6 nm to 16.7 nm with the increasing zinc doping concentration. FESEM images showed PbS nanocrystals on the surface of the films exhibited pyramidal shape, and the grain size became smaller with the increasing doping concentration. The AFM results showed that the root mean square roughness of the PbS film has been reduced due to Zn doping. The optical properties of films were explored by UV–vis–NIR spectrophotometer in the range from 400 to 2400 nm, the optical bandgap value of PbS films increased from 1.14 eV to 1.74 eV. All as-deposited films were p-type semiconducting. Among them, the 3 at.% Zn-PbS thin films possessed the lowest resistivity (10.8 Ω -cm), the highest carrier concentration (2.82 × 1017 cm−3) and carrier mobility (11.2 cm−2V−1s−1). A new ideal bandgap (1.39 eV) absorber composition (1 at.% Zn-doped PbS film) was rationally designed and facilely developed. Our work presents a promising potential for ideal bandgap absorber layer of solar cells.

Layered molybdenum disulphide (MoS2) can efficiently emit photoluminescence (PL) excited by visible light. However, one-photon PL of MoS2 for bioimaging purposes suffers from strong autofluorescenc ...

Multi-photon upconversion super-resolution microscopy is a recently proposed imaging modality, based on lanthanide-doped nanocrystals, which can emit visible emission upon low-intensity near-infrared excitation. This imaging modality exhibits many advantages, including increased imaging depth, high signal-to-noise ratio, low phototoxicity, and high photostability. However, two factors seriously restrict its scanning speed, sometimes even to an intolerable degree; the long lanthanide emission lifetime and the low brightness. For proper imaging, pixel dwell times of several milliseconds are often required. In this work, a facile strategy is proposed to overcome these two obstacles. By adopting a high sensitizer (Yb3+) doping strategy for upconversion nanocrystals, their emission intensity is greatly increased and their emission transients are significantly accelerated, without losing the emission depletion efficiency induced by the depletion laser. This enables the implementation of a very fast upconversion stimulated emission depletion super-resolution microscopy with a scanning speed of 10 μs per pixel. This work opens the possibility for upconversion super-resolution microscopy to capture vital biological activities in real time.

Stimulated emission depletion (STED) microscopy achieved with lanthanide-doped upconversion nanoparticles (UCNPs) exhibits many outstanding advantages such as low-power illumination, near-infrared (NIR) excitation, and high photostability. However, the available types of UCNP-STED probes are very limited and rely greatly on the specific depletion mechanism. Here, by combining the STED and the energy migration upconversion processes, emissions of Tb3+, Eu3+, Dy3+, and Sm3+ distributed in the shell can all be depleted by interrupting the injected energy flux from the Tm3+-doped core nanoparticles. With the merit of the proposed strategy, new types of UCNP-STED probes are demonstrated to perform emission-varying STED imaging with one single, fixed pair of low-power NIR continuous wave lasers.

Lanthanide-doped upconversion nanoparticles (UCNPs) are promising bioimaging nanoprobes due to their excellent photostability. As one of the most commonly used lanthanide activators, Tm3+ ions have perfect ladder-type electron configuration and can be directly excited by bio-friendly near-infrared-II (NIR-II) wavelengths. Here, the emission characteristics of Tm3+-doped nanoparticles under laser excitations of different near-infrared-II wavelengths were systematically investigated. The 1064 nm, 1150 nm, and 1208 nm lasers are proposed to be three excitation strategies with different response spectra of Tm3+ ions. In particular, we found that 1150 nm laser excitation enables intense three-photon 475 nm emission, which is nearly 100 times stronger than that excited by 1064 nm excitation. We further optimized the luminescence brightness after investigating the luminescence quenching mechanism of bare NaYF4: Tm (1.75%) core. After growing an inert shell, a ten-fold increase of emission intensity was achieved. Combining the advantages of NIR-II wavelength and the higher-order nonlinear excitation, a promising facile excitation strategy was developed for the application of thulium-doped upconversion nanoparticles in nanoparticles imaging and cancer cell microscopic imaging.

Photodynamic therapy (PDT), a clinically approved cancer treatment strategy, features non-invasiveness, few side-effects, high spatial resolution, etc. The advancement of PDT has been significantly restricted by the penetration depth of the excitation light. Herein, an effective fluorogen, TBD, with aggregation-induced emission characteristics (AIEgen) and high reactive-oxygen-species (ROS) generation efficiency was reported and integrated with a near infrared (NIR) light excitable upconversion nanoparticle (UCNP) to construct NIR light excitable UCNP@TBD nanocomposites. The formed nanocomposite has excellent photostability, good biocompatibility, and efficient ROS generation under NIR light excitation via Forster resonance energy transfer (FRET), enabling NIR light excited PDT. Moreover, the proposed NIR light excited PDT can break the impasse between the penetration depth and excitation volume in conventional PDT, effectively improving the anticancer therapeutic outcome. In vitro cancer cell ablation and in vivo tumor growth inhibition validated that the proposed UCNP@TBD nanocomposite is a promising NIR light excitable PDT agent with great potential for future translational research.

Overtone Vibrational Transition-Induced Lanthanide Excited-State Quenching in Yb3+/Er3+-Doped Upconversion Nanocrystals

Fluorescent carbon dots (FCDs) have received considerable attention because of the great potential for a wide range of applications, from bioimaging to optoelectronic devices. In this work, we reported the synthesis of nitrogen-doped FCDs with an average size of 2 nm in a subcritical water apparatus by using biomass waste (i.e., expired milk) as the precursor. The obtained FCDs were highly dispersed in aqueous solution because of the presence of O-containing functional groups on their surfaces. Under the excitation of ultraviolet and blue light, the FCDs exhibited excitation wavelength-dependent fluorescence in the emission range of 400–550 nm. The FCDs could be easily taken up by HeLa cells without additional surface functionalization, serving as fluorescent nanoprobes for bioimaging. The applications of FCDs as sensing agents for the detection of Fe3+, solid-state fluorescent patterning, and transparent hybrid films were also performed, demonstrating their potential for solid-state fluorescent sensing, security labeling, and wearable optoelectronics.

Two novel tetranuclear compounds with general formula of [Ln4L4(µ3-OH)4(DMF)x(MeOH)y] (compound 1, Ln = Yb, x = 3, y = 1; compound 2, Ln = Tb, x = 4, y = 0) were synthesized via simple hydrothermal reaction by using lanthanide nitrate and H2L as reactants. The crystal structure of compounds 1 and 2 were in triclinic P − 1 monoclinic P2/c space group, respectively, as evidenced by single crystal X-ray diffraction. Both of them show the coordination features, namely, a distorted tetranuclear lanthanide Ln4(OH)4 cubane core consisting of four µ3-OH− bridges, while four H2L ligands and four solvent molecules occupy the peripheral part of the cluster. Interestingly, compound 1 exhibits near infrared luminescence upon excitation at 530 nm because of Yb3+ ion. Furthermore, Compound 1 shows efficient two-photon upconversion property. Magnetic susceptibility measurements indicate that compounds 1 and 2 show an antiferromagnetic interaction between the adjacent Ln3+ ions.

Nanomedicine utilizes biocompatible nanomaterials for therapeutic purposes to treat various diseases. Flavonoids present in the plant materials act as both reducing and electrostatic stabilizing agents for the ‘Green’ synthesis of metal nanomaterials. Further, these nanomaterials are effectively used to treat various cancer cells and pathogenic microbes. The experimental approach for flavonoids-mediated nanomaterial (FMN) synthesis is simple, rapid, cost-effective and reproducible. However, the detailed reports on synthesis, mechanism, and in vivo application of FMN are very limited in literatures. Thus, this focused review will definitely help researchers who are working on biocompatible nanomaterial synthesis and application in biomedical sector. Further, this is the first review to discuss the significance, mechanisms, and future trends of FMN. The FMN and their dual function as both nano-carrier and nano-drug in various biomedical sectors might be a hot research topic in upcoming days.

We experimentally realized one-scan fluorescence emission difference nanoscopy (FED) by simultaneously imaging two different color emissions of NaYF4:Er3+@NaYF4@NaYF4:Yb3+/Tm3+ upconversion nanoparticles. Under the irradiation of two synchronized laser beams, a solid 940 nm beam and a hollow 808 nm beam, green emission of Er3+ and blue emission of Tm3+ can be orthogonally generated and collected. After simple subtraction, a resulting super-resolution image featuring 54 nm resolution was obtained. This strategy of excitation orthogonality would greatly improve the imaging speed and the applicability of FED nanoscopy.

Stimulated emission depletion microscopy provides a powerful sub-diffraction imaging modality for life science studies. Conventionally, stimulated emission depletion requires a relatively high light intensity to obtain an adequate depletion efficiency through only light–matter interaction. Here we show efficient emission depletion for a class of lanthanide-doped upconversion nanoparticles with the assistance of interionic cross relaxation, which significantly lowers the laser intensity requirements of optical depletion. We demonstrate two-color super-resolution imaging using upconversion nanoparticles (resolution ~ 66 nm) with a single pair of excitation/depletion beams. In addition, we show super-resolution imaging of immunostained cytoskeleton structures of fixed cells (resolution ~ 82 nm) using upconversion nanoparticles. These achievements provide a new perspective for the development of photoswitchable luminescent probes and will broaden the applications of lanthanide-doped nanoparticles for sub-diffraction microscopic imaging., Upconversion nanoparticles, which do not suffer from the photophysical artifacts that limit fluorescent molecules, offer an exciting opportunity for biological super-resolution imaging. Here, Zhan et al. develop an efficient STED mechanism using optimized lanthanide upconversion nanoparticles, enabling cytoskeleton nanoscopic imaging.

We successfully synthesized AuAg-alloyed nanoprisms (AuAgNPrisms) through the seed mediated and galvanic replacement approaches. By introducing the synthesized AuAgNPrisms at the buffer/active interface with an optimal concentration, we increased the power conversion efficiency of PTB7:PC70BM-based organic photovoltaic cells from 6.58% to 7.11%, the current density from 13.36 to 15.01 mA/cm2, corresponding to enhancement factors of 8.1% and 12.4%, respectively. According to our systematical study, we concluded that the incorporation of AuAgNPrisms not only increases light absorption in the active layer over a broad wavelength range but improves the exciton dissociation rate at the interface between PTB7 and PC70BM. With the incorporation of AuAgNPrisms, although the increase in the leakage current is observed, the carrier mobility is also improved apparently, yielding that the reduction in the fill factor is negligible. This work could contribute to the development of high efficiency and low cost organic solar cells.

The synthesis of fluorescent nanomaterials has received considerable attention due to the great potential of these materials for a wide range of applications, from chemical sensing through bioimaging to optoelectronics. Herein, we report a facile and scalable approach to prepare fluorescent carbon dots (FCDs) via a one-pot reaction of citric acid with ethylenediamine at 150 °C under ambient air pressure. The resultant FCDs possess an optical bandgap of 3.4 eV and exhibit strong excitation-wavelength-independent blue emission (λEm = 450 nm) under either one- or two-photon excitation. Owing to their low cytotoxicity and long fluorescence lifetime, these FCDs were successfully used as internalized fluorescent probes in human cancer cell lines (HeLa cells) for two-photon excited imaging of cells by fluorescence lifetime imaging microscopy with a high-contrast resolution. They were also homogenously mixed with commercial inks and used to draw fluorescent patterns on normal papers and on many other substrates (e.g., certain flexible plastic films, textiles, and clothes). Thus, these nanomaterials are promising for use in solid-state fluorescent sensing, security labeling, and wearable optoelectronics.

Nanohybrids can in most cases kill cancer cells more efficiently as compared with free photosensitizers. In this work, we constructed nanohybrid Ru1@CDs composed of carbon nanodots (CDs) and a phosphorescent Ru(ii) complex (Ru1) for one- and two-photon photodynamic therapy of cancer. The photosensitizer and imaging agent Ru1 is decorated onto the nanocarrier CDs covalently. Ru1 and Ru1@CDs can penetrate into cancer cells through an energy-dependent mechanism and endocytosis, respectively. Both Ru1 and Ru1@CDs are capable of lysosome-targeted phosphorescence imaging and photodamage under either 450 nm (one-photon) or 810 nm (two-photon) excitation. Conjugation with CDs can increase the cellular uptake efficacy of Ru1. Mechanism investigations show that both Ru1 and Ru1@CDs can induce apoptosis through generation of reactive oxygen species and cathepsin-initiated apoptotic signaling pathways. Upon two-photon excitation, Ru1@CDs show better penetrability, as well as higher inhibitory effects on cancer cell growth in both 2D cell and 3D multicellular tumor spheroid models. Our work provides an effective strategy for the construction of multifunctional imaging and phototherapeutic nanohybrids for the treatment of cancer.

Red-emitting carbon dots (C-dots) were synthesized from p-phenylenediamine (p-PD) aqueous solution with nitric acid (HNO3) assistance by hydrothermal reaction at 200 °C for 2 h. p-PD aqueous solution can be transferred to C-dots (or poly(p-PD)) with (or without) the addition of acid. Different acid systems, such as HNO3, H3PO4 and HF, can directly synthesize red-emitting C-dots, and the fluorescence can be enhanced by increasing the strength of acids. N-CDs, 3.46 nm-average-sized C-dots, prepared in dilute HNO3, have a quantum yield of 15.8% with unique, excitation-wavelength independent emission in the red region (600 and 680 nm) and a broad visible excitation band. Carboxyl, ester and hydroxyl groups on the C-dots surface directly lead to red emission. N-CDs have a certain selective specificity for Fe3+ detection and the linear range is 10–300 nmol L−1 with a limit of determination of 1.9 nmol L−1.

Precise knowledge about optical and structural performance of individual rare earth (RE)-doped particles is extremely important for the optimization of luminescent particles and for fully exploiting their capability as multifunctional probes for interdisciplinary applications. In this work, optical and structural anisotropy of individual particles through RE-doped single fluoride microcrystals with controllable morphology is reported. Unique luminescent phenomena, for example, white light-emission from Pr

In this study, we systematically investigate the decay characteristics of upconversion luminescence (UCL) under anti-Stokes excitation through numerical simulations based on rate-equation models. We find that a UCL decay profile generally involves contributions from the sensitizer's excited-state lifetime, energy transfer and cross-relaxation processes. It should thus be regarded as the overall temporal response of the whole upconversion system to the excitation function rather than the intrinsic lifetime of the luminescence emitting state. Only under certain conditions, such as when the effective lifetime of the sensitizer's excited state is significantly shorter than that of the UCL emitting state and of the absence of cross-relaxation processes involving the emitting energy level, the UCL decay time approaches the intrinsic lifetime of the emitting state. Subsequently, Stokes excitation is generally preferred in order to accurately quantify the intrinsic lifetime of the emitting state. However, possible cross-relaxation between doped ions at high doping levels can complicate the decay characteristics of the luminescence and even make the Stokes-excitation approach fail. A strong cross-relaxation process can also account for the power dependence of the decay characteristics of UCL. QC 20190318

Two alkaline-earth metal coordination polymers, [Ca(TAPIP)2(H2O)3]·2H2O (1) and [Ca(TAPIP)2(H2O)3]·5H2O (2), have been synthesized under hydrothermal reactions with the imidazo[4,5-f][1, 10]phenanthroline derivate D-π-A type ligand, 2-(4-(1H-1,2,4-triazol-1-yl)phenyl)-1H-imidazo[4,5-f][1, 10]phenanthroline (TAPIP). Complexes 1 and 2 crystallize in different lattice groups and are discrete coordinate structures in which the two planes of TAPIP ligands are nearly coplanar and perpendicular, respectively. Moreover, in 2 an interesting infinite water chain is captured. In exploring their one/two-photon excited fluorescence, the results show that the original ligand and 1 exhibit similar fluorescent properties while 2 gives off orange light and shows much stronger two-photon excited fluorescent properties which might result from the different torsion angles and/or stacking modes of the organic ligands.

Photonic nanostructures with resonant modes that can generate large electric field (EF) enhancements are applied to enhance light-matter interactions in nanoscale, bringing about great advances in both fundamental and applied science. However, a small hot spot (i.e., the regions with strong EF enhancements) and highly inhomogeneous EF distribution of the resonant modes usually hinder the enhancements of light-matter interactions in a large spatial scale. Additionally, it is a severe challenge to simultaneously generate multiple resonant modes with strong EF enhancements in a broadband spectral range, which greatly limits the capacity of a photonic nanostructure in boosting optical responses including nonlinear conversion, photoluminescence, etc. In order to overcome these challenges, we presented an arrayed hyperbolic metamaterial (AHMM). This AHMM structure is applied to simultaneously enhance the three-photon and four-photon luminescence of upconversion nanoparticles. Excitingly, the enhancement of the three-photon process is 1 order of magnitude larger than previous records, and for the enhancing four-photon process, we achieve an enhancement of 3350 times, greatly beneficial for overcoming the crucial problem of low efficiency in near infrared light upconversion. Our results demonstrated a promising platform for realizing giant enhancements of light-matter interactions, holding potential in constructing various photonics applications such as the nonlinear light sources.

Engineering a facile and controllable approach to modulate the spectral properties of lanthanide-doped upconversion nanoparticles (UCNPs) is always an ongoing challenge. Herein, long-range ordered, distinct two-dimensional (2D) binary nanoparticle superlattices (BNSLs) composed of NaREF4 :Yb/Er (RE = Y and Gd) UCNPs and plasmonic metallic nanoparticles (Au NPs), including AB, AB3 , and AB13 lattices, are fabricated via a slow evaporation-driven self-assembly to achieve plasmonic modulation of upconversion luminescence (UCL). Optical measurements reveal that typical red-green UCL from UCNPs can be effectively modulated into reddish output in BNSLs, with a drastically shortened lifetime. Notably, for AB3 - and AB13 -type BNSLs with more proximal Au NPs around each UCNP, modified UCL with fine-structured spectral lineshape is observed. These differences could be interpreted by the interplay of collective plasmon resonance introduced by 2D periodic Au arrays and spectrally selective energy transfer between UCNPs and Au. Thus, fabricating UCNP-Au BNSLs with desired lattice parameters and NP configurations could be a promising way to tailor the UCL through controlled plasmonic modulation.

We report on a rapid method to synthesize gold nanobipyramids that utilizes a hexagonal liquid crystal as a frame, suggesting a liquid crystal accelerated growth process. The method represents an improvement in processing time as compared to previously reported methods. Furthermore, as the bulk of the total processing time is required by a purification step, the method presented in this paper holds the promise of an order of magnitude improvement of processing time by further optimization of the growth process that would eventually eliminate the need for purification.

The perfect energy level overlap of 2H11/2, 4S3/2, and 4F9/2 in Er3+ ions with those of 5F3, 5F4/5S2, and 5F5 in adjacently codoped Ho3+ ions allows efficient interenergy transfer. Therefore, in addition to routine activators, Er3+ or Ho3+ can further act as sensitizers to transfer the upconverted energy to nearby Ho3+ or Er3+, resulting in enhanced upconversion luminescence due to the emission overlap. Proper codoping of Er3+/Ho3+ or Ho3+/Er3+ obviously elevates the maximum doping concentration (thus producing additional upconverted photons) to a level higher than that causing luminescence quenching and significantly enhances upconversion emissions compared with those of singly Er3+ or Ho3+-doped host materials. Indeed, the so-far strongest red upconversion emission under 1532 nm excitation was obtained in LiYF4:Er/Ho@LiYF4 nanoparticles and Ho3+-sensitized Er3+ upconversion emissions excited by 1150 nm laser was simultaneously discovered. With great enhancement compared with that of singly Ho3+ doped co...

Red-emitting carbonized polymer dots (CPDs) was prepared from p-phenylenediamine (p-PD) aqueous solution with the assistance of sulfuric acid (H2SO4), and the optical properties and bio-imaging application were studied in this paper. Compared with other strong acids-assisted systems, SA-CPDs (prepared from H2SO4-assisted system, average diameter is ~ 5 nm) is the brightest. The photoluminescence Quantum Yields (QYs) is 21.4% (in water), and the product yield is 16.5%. SA-CPDs aqueous solution emits at 600 nm when excited by the light from 300 to 580 nm. The emission wavelength is independent on the excitation wavelength. Formation energies of CPDs in two ways were calculated to show that longitudinal growth (forming polymers) is difficult, and the transverse growth (forming CPDs) is easy. In addition, the two-photon photoluminescence properties (emitting at 602 nm when excited by 850 nm femtosecond pulse laser) of SA-CPDs were also utilized in the experiments for HeLa cells staining and shown to have potential applications in bio-imaging.

Figure S1. Photos of CPDs samples under UV light (365 nm). Figure S2. The optimization process for HA-CPDs preparation with HCl-assisted p-PD system. Figure S3. (a) The suitable c (p-PD) range for the preparation of red CPDs at the optimized c (acid):c (p-PD) ratio. (b) QYs data and the intensity plots as a function of absorbance for the as-prepared CPDs excited at 365 nm. Samples in (a) were excited at 365 nm. (c) Photographs of all as-prepared and diluted C-dots samples under daylight and 365 nm UV light. (d) SA-CPDs powders and (e) the re-dissolved solution. (DOC 1178 kb)

Upconversion nanoparticles, which do not suffer from the photophysical artifacts limiting fluorescent molecules, offer an exciting opportunity for biological super-resolution imaging. We develop an efficient STED mechanism using lanthanide upconversion nanoparticles, enabling cytoskeleton nanoscopic imaging.

Upconversion nanoparticles exhibit ordinary emission brightness for the existence of non-radiative transition induced by the surface defects, which fundamentally limits their promising applications. Here, a reconstruction process to rule out the amorphous layer and defects related to the surface of the as-synthesized particles is achieved with the use of 980-nm continuous laser irradiation. More importantly, the uniform morphology and monodispersibility of these nanoparticles are well preserved. Local heat induced via photothermal conversion of laser irradiation with the association with non-harmonic phonon coupling contributes to a tremendous improvement on the integral upconversion luminescence intensity. The upconversion intensity of Er3+ ions in sub–10-nm Ba2LaF7 nanoparticles enhances by more than 313-fold in the red emission, and subsequently, a bright luminescence originated from an individual particle could be observed under a multiphoton laser scanning luminescence microscopy. Our results suggest that this strategy could be extended to GdF3, KLu2F7, and BaGdF5 systems, which exhibit drastic enhancement of emission intensity unambiguously. The laser-induced surface reconstruction in this work is demonstrated to provide a direct and facile approach to enhance the upconversion intensity, which could offer the possibility for achieving high-resolution imaging.

Nd3+-sensitized upconversion nanoparticles (UCNPs) can be excited by both 980 and 808 nm light, which is regarded as a particularly advantageous property of these particles. In this work, we demonstrate that the nanoparticles can exhibit significantly different response when excited at these two excitation wavelengths, showing dependence on the intensity of the excitation light and the way it is distributed in time. Specifically, with 808 nm excitation saturation in the emitted luminescence is more readily reached with increasing excitation intensities than upon 980 nm excitation. This is accompanied by delayed upconversion luminescence (UCL) kinetics and weaker UCL intensities. The different luminescence response at 808 and 980 nm excitation reported in this work is relevant in a manifold of applications using UCNPs as labels and sensors. This could also open new possibilities for multi-wavelength excitable UCNPs for upconversion color display and in laser-scanning microscopy providing selective readouts and sub-sectioning of samples.