High-intensity first near-infrared emission through energy migration in multilayered upconversion nanoparticles.

The development of Tm3+ 807 nm first near-infrared (NIR-I, 700-1000 nm) emission with second near-infrared (NIR-II, 1000-1700 nm) excitation is urgently needed, due to its potential application in biomedicine. In this work, a range of NaErF4:Yb@NaYF4:Yb@NaYF4:Yb,Tm@NaYF4 multilayer core-shell structure upconversion nanoparticles (UCNPs) were successfully prepared by a co-precipitation method. The strongest UC emissions can be obtained by changing the concentration of Yb3+ in the core and the first shell, and the proposed UC process was discussed in detail. The analysis shows that high-intensity NIR-I emission (807 nm) from Tm3+ and visible light from Er3+ were achieved through the energy migration among Yb3+ and the energy back transfer from Yb3+ to Er3+ under 1532 nm excitation. Besides, compared to bilayer UCNPs, multilayer core-shell UCNPs display superior optical performance. The high-intensity NIR-I emission at 807 nm (Tm3+:3H4 → 3H6) under 1532 nm NIR-II excitation demonstrates huge advantages in bioimaging.

Enhanced internal field of Bi4NbO8Cl ferroelectric photocatalyst to promote charge separation via constructing crystal plane-dependent BiOI dielectric layer.

Spontaneous polarization induced by the unique crystal structure of ferroelectric semiconductor photocatalyst facilitates charge separation and injects new vitality into the improvement of the photocatalytic activity. However, due to the complexity of multi-electric field coupling, the actual efficiency of charge separation driven by the depolarization field is restricted by the shielding field, which is lower than theoretical expectations. Here, we take Bi4NbO8Cl as a model system and selectively construct a BiOI dielectric layer on its positive polarized surface through the adsorption-self-assembly method, aiming to reduce the attenuation of the shielding field to the depolarization field. The enhanced residual depolarization field (RDF) is quantitatively characterized by ferroelectric performance test. Moreover, the charge transfer path and final position are elaborated by photo-deposition experiments, while high-quality interface and calculated difference of the potential between Bi4NbO8Cl and BiOI is responsible for the formation of charge transfer channel. The enhanced RDF promotes the separation of charges, which causes that Bi4NbO8Cl/BiOI photo-degradation of bisphenol A (BPA) gives 7.35-fold greater efficiency than Bi4NbO8Cl. This scheme of weakening the shielding field by surface reconstruction engineering is promising to be extended to more ferroelectric photocatalyst systems.

Diverse Functionalization of Tetrahydro-ß-carbolines or Tetrahydro-γ-carbolines via Oxidative Coupling Rearrangement.

We report herein diverse functionalization of tetrahydro-ß-carbolines (THßCs) or tetrahydro-γ-carbolines (THγCs) via oxidative coupling rearrangement. The treatment of THßCs or THγCs with t-BuOOH (TBHP) afforded 3-peroxyindolenines, followed by HCl catalyzed indolation to form unexpected 2-indolyl-3-peroxyindolenines. Further rearrangement of these peroxides allows for rapid access to a skeletally diverse chemical library in good to excellent yields.

Mechanistic insights on the reaction behaviors of the acrylonitrile selective catalytic combustion over Cu-based UZM-9.

In this paper, a series of Cu-based UZM-9 catalysts were prepared via modified aqueous ion exchange and the performance of acrylonitrile (AN) selective catalytic combustion (SCC) over these catalysts were investigated, and further characterized by Ar adsorption-desorption, ICP, XRD, H2-TPR and XPS. Among which, Cu-11.5 catalyst exhibited a complete AN conversion at 270 °C together with N2 selectivity higher than 98% during the whole temperature range when water was present. Meantime, the isolated Cu2+ was the main active sites, which could be reduced to Cu+ during -CN oxidation, then reoxidized to Cu2+ by O2. Besides, the mechanism of AN SCC over Cu-11.5 was systematically investigated by in situ DRIFTS, which revealed that both the temperature and H2O contents could influence the main N-containing intermediate and the reaction mechanism. In low and high temperature region, the reaction followed hydrolysis mechanism. Within medium temperature range, the reaction mechanism of AN oxidation was strongly associated with the water content. Oxidation was dominant at water-free condition, while oxidation and hydrolysis coexisted at relatively low water content (0.3%). When water content reached up to 0.9% or more, hydrolysis was the principal reaction. Finally, the hydrothermal stability of Cu-based UZM-9 catalysts were illustrated.

Synthesis and potent cytotoxic activity of a novel diosgenin derivative and its phytosomes against lung cancer cells.

Diosgenin (Di), a steroidal sapogenin derived from plants, has been shown to exert anticancer effects in preclinical studies. Using Di as a starting material, various Di derivatives were designed and synthesized, aiming to discover new steroid-based antitumor agents. In this work, we synthesized several Di derivatives and screened FZU-0021-194-P2 (P2), which showed more potent cytotoxic activities against human non-small-cell lung cancer A549 and PC9 cells. Considering that Di has a unique sterol structure similarly to cholesterol, P2 phytosomes (P2Ps) were prepared to further improve the water solubility of P2. The P2Ps exhibited a particle size of 53.6 ± 0.3 nm with oval shape and a zeta potential of -4.0 ± 0.7 mV. P2Ps could inhibit the proliferation of lung cancer cells more efficiently than Di phytosomes after 72 h of incubation time by inducing cell cycle arrest and apoptosis. The results indicated that P2Ps could be a promising anticancer formulation for non-small-cell lung cancer.

Manipulation of Water for Diversified Functionalization of Tetrahydro-ß-carbolines (THßCs) with Indoles.

Water plays a crucial role in organic synthesis. However, diversified functionalization manipulated by water is still rare and remains unexplored. Herein, we report the first water-manipulated protocol to achieve the diversified functionalization of tetrahydro-ß-carbolines (THßCs) in an open flask at room temperature that exhibit a broad functional-group tolerance. More water leads to monoarylation, while less water leads to diarylation. Further one-step transformation afforded oxidized bis(indolyl)methanes, eudistomin U, and the related derivatives in satisfactory yields.

Enhanced Red Emission in Er3+-Sensitized NaLuF4 Upconversion Crystals via Energy Trapping.

Luminescence efficiency of trivalent lanthanide-doped upconversion (UC) materials is significantly limited by luminescence concentration quenching. In this work, red UC emission is dramatically enhanced in Er3+-sensitized NaLuF4 UC crystals through energy trapping under multiple excitation wavelengths. Cross-relaxation quenching and the energy migration to internal lattice defects are simultaneously suppressed by confining the excitation energy in the Er3+ activator after introducing the Tm3+ or Ho3+ energy trapping center. The enhanced red UC emission (Er3+: 660 nm) mainly comes from the effective excitation energy confinement by Tm3+ and Ho3+ trapping centers through an easy energy transfer between Er3+ and Tm3+/Ho3+: 4I11/2 (Er3+) → 3H5 (Tm3+) → 4I13/2 (Er3+) and 4I11/2 (Er3+) → 5I6 (Ho3+) → 4I13/2 (Er3+). It is found that the confining efficiency of excitation energy in Er3+-sensitized NaLuF4 crystals is higher than that in Yb3+/Er3+ cosensitized NaLuF4 crystals, and the luminescence efficiency of Er3+-sensitized NaLuF4 crystals is much higher than that of Er3+-based host sensitization UC crystals (NaErF4). Moreover, Er3+-sensitized UC particles can be efficiently excited by three different wavelengths (808, 980, and 1532 nm), indicating huge advantages for applications in bioimaging, anticounterfeiting, and solar cells.

Biomimetic Oxidative Coupling Cyclization Enabling Rapid Construction of Isochromanoindolenines.

Herein, we report a biomimetic oxidative coupling cyclization strategy for the highly efficient functionalization of tetrahydrocarbolines (THCs). This process enables rapid access to complex isochromanoindolenine scaffolds in moderate to excellent yields. The reaction proceeds smoothly and rapidly (complete within minutes) in an open flask. This operationally simple protocol is scalable and compatible with a wide range of functional groups. Late-stage functionalization of a pharmacologically relevant molecule is also demonstrated.

Facile synthesis and emission enhancement in NaLuF4 upconversion nano/micro-crystals via Y3+ doping.

A series of Y3+-absent/doped NaLuF4:Yb3+, Tm3+ nano/micro-crystals were prepared via a hydrothermal process with the assistance of citric acid. Cubic nanospheres, hexagonal microdisks, and hexagonal microprisms can be achieved by simply adjusting the reaction temperature. The effect of Y3+ doping on the morphology and upconversion (UC) emission of the as-prepared samples were systematically investigated. Compared to their Y3+-free counterpart, the integrated spectral intensities in the range of 445-495 nm from α-, ß-, and α/ß-mixed NaLuF4:Yb3+, Tm3+ crystals with 40 mol% Y3+ doping are increased by 9.7, 4.4, and 24.3 times, respectively; red UC luminescence intensities in the range of 630-725 nm are enhanced by 4.6, 2.4, and 24.9 times, respectively. It is proposed that the increased UC emission intensity is mainly ascribed to the deformation of crystal lattice, due to the electron cloud distortion in host lattice after Y3+ doping. This paper provides a facile route to achieve nano/micro-structures with intense UC luminescence, which may have potential applications in optoelectronic devices.

A novel anion doping strategy to enhance upconversion luminescence in NaGd(MoO4)2:Yb3+/Er3+ nanophosphors.

We propose a novel and efficient F- anion doping strategy for enhancing upconversion luminescence in upconversion nanophosphors. NaGd(MoO4)2:Yb3+/Er3+ nanophosphors doped with different F- contents are synthesized hydrothermally. Rietveld refinement results obtained from X-ray diffraction data indicate that the Gd-O bond length decreases and the O-Gd-O bond angle varies with increasing F- content, resulting in augmented local crystal field strength and distorted local site symmetry of the dopant lanthanide sites. Judd-Ofelt analysis suggests that the calculated radiative quantum efficiency of the 4S3/2 level and the radiative branching ratio of 4S3/2 → 4I15/2 transition in F--doped NaGd(MoO4)2:Yb3+/Er3+ nanophosphors are much greater than those in F- anion-free samples. It is inferred that F- anion doping helps to reduce the nonradiative transition probabilities based on the luminescence dynamics. Rietveld refinement results and Judd-Ofelt analysis confirm jointly that doping of interstitial F- anions could enhance local crystal field strength with odd parity and modify site symmetry of the lanthanide activator ions, leading to enhanced radiative transitions and inhibited nonradiative transitions. A maximum of 17-fold enhancement of total emission intensity is found in NaGd(MoO4)2:Yb3+/Er3+/F- nanophosphors compared with F- anion-free counterparts. The proposed F- anion doping strategy provides an alternative approach for enhancing upconversion luminescence efficiency and could be extended to other inorganic upconversion nanomaterials.

Lanthanide-Doped KLu2F7 Nanoparticles with High Upconversion Luminescence Performance: A Comparative Study by Judd-Ofelt Analysis and Energy Transfer Mechanistic Investigation.

The development, design and the performance evaluation of rare-earth doped host materials is important for further optical investigation and industrial applications. Herein, we successfully fabricate KLu2F7 upconversion nanoparticles (UCNPs) through hydrothermal synthesis by controlling the fluorine-to-lanthanide-ion molar ratio. The structural and morphological results show that the samples are orthorhombic-phase hexagonal-prisms UCNPs, with average side length of 80 nm and average thickness of 110 nm. The reaction time dependent crystal growth experiment suggests that the phase transformation is a thermo-dynamical process and the increasing F-/Ln3+ ratio favors the formation of the thermo-dynamical stable phase - orthorhombic KLu2F7 structure. The upconversion luminescence (UCL) spectra display that the orthorhombic KLu2F7:Yb/Er UCNPs present stronger UCL as much as 280-fold than their cubic counterparts. The UCNPS also display better UCL performance compared with the popular hexagonal-phase NaREF4 (RE = Y, Gd). Our mechanistic investigation, including Judd-Ofelt analysis and time decay behaviors, suggests that the lanthanide tetrad clusters structure at sublattice level accounts for the saturated luminescence and highly efficient UCL in KLu2F7:Yb/Er UCNPs. Our research demonstrates that the orthorhombic KLu2F7 is a promising host material for UCL and can find potential applications in lasing, photovoltaics and biolabeling techniques.

Single Upconversion Nanoparticle-Bacterium Cotrapping for Single-Bacterium Labeling and Analysis.

Detecting and analyzing pathogenic bacteria in an effective and reliable manner is crucial for the diagnosis of acute bacterial infection and initial antibiotic therapy. However, the precise labeling and analysis of bacteria at the single-bacterium level are a technical challenge but very important to reveal important details about the heterogeneity of cells and responds to environment. This study demonstrates an optical strategy for single-bacterium labeling and analysis by the cotrapping of single upconversion nanoparticles (UCNPs) and bacteria together. A single UCNP with an average size of ≈120 nm is first optically trapped. Both ends of a single bacterium are then trapped and labeled with single UCNPs emitting green light. The labeled bacterium can be flexibly moved to designated locations for further analysis. Signals from bacteria of different sizes are detected in real time for single-bacterium analysis. This cotrapping method provides a new approach for single-pathogenic-bacterium labeling, detection, and real-time analysis at the single-particle and single-bacterium level.

NaGd(MoO4)2 nanocrystals with diverse morphologies: controlled synthesis, growth mechanism, photoluminescence and thermometric properties.

Pure tetragonal phase, uniform and well-crystallized sodium gadolinium molybdate (NaGd(MoO4)2) nanocrystals with diverse morphologies, e.g. nanocylinders, nanocubes and square nanoplates have been selectively synthesized via oleic acid-mediated hydrothermal method. The phase, structure, morphology and composition of the as-synthesized products are studied. Contents of both sodium molybdate and oleic acid of the precursor solutions are found to affect the morphologies of the products significantly, and oleic acid plays a key role in the morphology-controlled synthesis of NaGd(MoO4)2 nanocrystals with diverse morphologies. Growth mechanism of NaGd(MoO4)2 nanocrystals is proposed based on time-dependent morphology evolution and X-ray diffraction analysis. Morphology-dependent down-shifting photoluminescence properties of NaGd(MoO4)2: Eu(3+) nanocrystals, and upconversion photoluminescence properties of NaGd(MoO4)2: Yb(3+)/Er(3+) and Yb(3+)/Tm(3+) nanoplates are investigated in detail. Charge transfer band in the down-shifting excitation spectra shows a slight blue-shift, and the luminescence intensities and lifetimes of Eu(3+) are decreased gradually with the morphology of the nanocrystals varying from nanocubes to thin square nanoplates. Upconversion energy transfer mechanisms of NaGd(MoO4)2: Yb(3+)/Er(3+), Yb(3+)/Tm(3+) nanoplates are proposed based on the energy level scheme and power dependence of upconversion emissions. Thermometric properties of NaGd(MoO4)2: Yb(3+)/Er(3+) nanoplates are investigated, and the maximum sensitivity is determined to be 0.01333 K(-1) at 285 K.

Morphology evolution and pure red upconversion mechanism of ß-NaLuF4 crystals.

A series of ß-NaLuF4 crystals were synthesized via a hydrothermal method. Hexagonal phase microdisks, microprisms, and microtubes were achieved by simply changing the amount of citric acid in the initial reaction solution. Pure red upconversion (UC) luminescence can be observed in ß-NaLuF4:Yb(3+), Tm(3+), Er(3+) and Li(+) doped ß-NaLuF4:20% Yb(3+), 1% Tm(3+), 20% Er(3+). Based on the rate equations, we report the theoretical model about the pure red UC mechanism in Yb(3+)/Tm(3+)/Er(3+) doped system. It is proposed that the pure red UC luminescence is mainly ascribed to the energy transfer UC from Tm(3+):(3)F4 → (3)H6 to Er(3+):(4)I11/2 → (4)F9/2 and the cross-relaxation (CR) effect [Er(3+):(4)S3/2 + (4)I15/2 → (4)I9/2 + (4)I13/2] rather than the long-accepted mechanism [CR process among Er(3+):(4)F7/2 + (4)I11/2 → (4)F9/2 + (4)F9/2]. In addition, compared to the Li(+)-free counterpart, the pure red UC luminescence in ß-NaLuF4:20% Yb(3+), 1% Tm(3+), 20% Er(3+) with 15 mol% Li(+) doping is enhanced by 13.7 times. This study provides a general and effective approach to obtain intense pure red UC luminescence, which can be applied to other synthetic strategies.

Tuning of structure and enhancement of upconversion luminescence in NaLuF4:Yb(3+),Ho(3+) crystals.

A series of NaLuF4:Yb(3+),Ho(3+) nano/micro-crystals with different crystal structures were synthesized via a hydrothermal method using citric acid as a chelating agent. The influences of NaF content, Li(+) doping, reaction temperature and reaction time on the crystal structure and shape of the as-synthesized NaLuF4 crystals were systematically investigated. To the best of our knowledge, it is the first time to report Li(+) doped α-NaLuF4:Yb(3+),Ho(3+) nanocrystals and the phase transformation by introducing Li(+) in NaLuF4 crystals. As for Li(+) doped α-NaLuF4, UC luminescence intensities of green emission (538 nm) and red emission (644 nm) in α-NaLuF4:Yb(3+),Ho(3+) nanocrystals with 20 mol% Li(+) doping are enhanced by 20 and 3.5 times compared to their Li(+)-free counterpart. As for Li(+) doped α/ß-mixed NaLuF4, with the increase of Li(+) content, the phase transforms from the α/ß-mixed phase to hexagonal then to cubic. UC emissions of 538 nm and 644 nm in NaLuF4:Yb(3+),Ho(3+) crystals doped with 5 mol% Li(+) are enhanced by 26.5 and 23 times, respectively. Besides, it is found that with the higher temperature and prolonged time, the morphology of NaLuF4 changes from nanoparticles to microtubes, resulting in the dramatic increase of UC emission intensity. The effects of Li(+) doping, reaction temperature and reaction time on the enhancement of UC emission intensity are discussed in detail. This study provides an effective and facile approach to obtain nano/micro-crystals with controllable structures and excellent optical properties.

Tunable multicolor and white-light upconversion luminescence in Yb3+/Tm3+/Ho3+ tri-doped NaYF4 micro-crystals.

NaYF4 micro-crystals with various concentrations of Yb(3+) /Tm(3+) /Ho(3+) were prepared successfully via a simple and reproducible hydrothermal route using EDTA as the chelating agent. Their phase structure and surface morphology were studied using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD patterns revealed that all the samples were pure hexagonal phase NaYF4. SEM images showed that Yb(3+)/Tm(3+)/Ho(3+) tri-doped NaYF4 were hexagonal micro-prisms. Upconversion photoluminescence spectra of Yb(3+)/Tm(3+)/Ho(3+) tri-doped NaYF4 micro-crystals with various dopant concentrations under 980 nm excitation with a 665 mW pump power were studied. Tunable multicolor (purple, purplish blue, yellowish green, green) and white light were achieved by simply adjusting the Ho(3+) concentration in 20%Yb(3+)/1%Tm(3+)/xHo(3+) tri-doped NaYF4 micro-crystals. Furthermore, white-light emissions could be obtained using different pump powers in 20%Yb(3+)/1%Tm(3+)/1%Ho(3+) tri-doped NaYF4 micro-crystals at 980 nm excitation. The pump power-dependent intensity relationship was studied and relevant energy transfer processes were discussed in detail. The results suggest that Yb(3+)/Tm(3+) Ho(3+) tri-doped NaYF4 micro-crystals have potential applications in optoelectronic devices such as photovoltaic, plasma display panel and white-light-emitting diodes.

A general top-down approach to synthesize rare earth doped-Gd2O3 nanocrystals as dualmodal contrast agents.

Dualmodal contrast agents of rare earth doped gadolinium oxide (Gd2O3) nanoparticles with high spatial resolution for magnetic resonance imaging (MRI) and high sensitivity for fluorescence imaging have attracted intensive attention in biomedical imaging. However, the rare earth doped nanoparticles mentioned above have been so far synthesized by the hydrothermal method, which is a bottom-up method, requiring high purity chemical reagents and relying on the availability of the respective precursors and strict reaction conditions. Here, we propose a facile and environmentally friendly top-down technique to synthesize the rare earth doped-Gd2O3 nanocrystals at an ambient environment. Using this approach, we synthesize a series of Tm3+, Tb3+, and Eu3+ doped-Gd2O3 nanoparticle colloids and observe strong blue, green, and red visible fluorescence from the as-synthesized nanoparticle colloids. Cell confocal microscope images show that these synthesized nanoparticle colloids are good fluorescence imaging contrast agents. Taking Gd2O3:Eu3+ nanoparticles as an example, we evaluate their performance in MRI in vitro and in vivo. These results indicate that the synthesized rare earth doped-Gd2O3 nanocrystals can be used as MRI and fluorescence imaging dualmodal contrast agents. The developed technique is expected to be a general, facile and environmentally friendly strategy towards synthesizing rare earth doped nanoparticles for biomedical applications.