Fabrication of an S-Scheme Heterojunction Photocatalyst MoS2/PANI with Greatly Enhanced Photocatalytic Performance.

As a promising catalyst, MoS2 has been widely studied owing to its high chemical reactivity, excellent electrical carrier mobility, good optical properties, and narrow band gap. However, the high recombination rate of photoinduced charge carriers limits its practical application in photocatalysis. In this study, MoS2 was coupled with PANI to fabricate an S-scheme heterojunction MoS2/PANI. The synthesized products were characterized systematically, and their photocatalytic properties were evaluated by photocatalytic degradation of norfloxacin (NOR) and rhodamine B (RhB). The obtained results indicated that the fabricated MoS2/PANI inorganic-organic heterojunction displayed tremendously enhanced photocatalytic activity. The degradation efficiencies for 60 mg L-1 of NOR and RhB are 86 and 100% under the simulated sunlight irradiation for 1 h with 10 mg of catalyst, which are 13 and 47 times higher than those of pure MoS2, respectively. Interestingly, it is superior to the previously reported related materials. The remarkably enhanced photocatalytic activity of MoS2 is assigned to the high charge conductivity feature of PANI and the formed S-scheme heterojunction that result in a steric separation of holes and electrons and conserve the initial powerful redox ability of the parent catalysts. This study provides a facile method to greatly improve the photocatalytic activity of MoS2 and facilitates its application for highly efficient removal of organic pollutants, such as antibiotic drugs and organic dyes, utilizing solar energy.

Fabrication of a Heterojunction by Coupling a Metal-Organic Framework and N-Doped Carbon for the Photocatalytic Removal of Antibiotic Drugs with High Efficiency.

Norfloxacin (NOR) and tetracycline (TC), two widely used antibiotic drugs released to the aquatic environment, induce harm to ecosystems. In this study, an effective method was developed successfully to remove NOR and TC by photocatalysis with a novel heterojunction NC/NH2-MIL-53(Fe), which was fabricated by combining a metal-organic framework (MOF) material (NH2-MIL-53(Fe)) and N-doped carbon (NC) nanoparticles via a facile solvent thermal method. The prepared product exhibits outstanding photocatalytic efficiencies toward degradation of NOR and TC that are 15 and 6 times higher than those of pure NH2-MIL-53(Fe), respectively. Moreover, it is higher than those of the related materials reported previously. The greatly enhanced photocatalytic performance is assigned to the fabricated heterojunction with well-matched energy band gaps, where the NC acts as an efficient electron transfer/reservoir material to effectively promote the migration and transfer and restrain the recombination of charge carriers. In addition, the formed heterojunction increases specific surface area and light absorbance. The photocatalytic activity enhanced mechanism, degradation products, and pathway were investigated. The present study offers a novel strategy to significantly improve the photocatalytic performances of MOFs for highly efficient photocatalytic removal of antibiotic drugs in wastewater.

Fabrication of a Covalent Organic Framework-Based Heterojunction via Coupling with ZnAgInS Nanosphere with High Photocatalytic Activity.

Covalent organic frameworks (COFs) exhibit visible-light activity for the degradation of organic pollutants. However, the recombination rates of their photoinduced electron-hole pairs are relatively high, limiting their practical application. In this work, we fabricated a 1,3,5-triformylphloroglucinol (Tp) and p-phenylenediamine (Pa-1) (TpPa-1) COF-based heterojunction through coupling the TpPa-1 COF with a ZnAgInS nanosphere via a facile oil bath heating method. The results show that the prepared heterojunction exhibits outstanding catalytic activity for the degradation of high concentrations the antibiotic tetracycline (TC) and the dye rhodamine B (RhB), which is driven by simulated sunlight. Its degradation rates for RhB and TC were 30× and 18× higher than that of the pure TpPa-1 COF, respectively. The greatly enhanced photocatalytic performances can be ascribed to the formed heterojunction with good band-gap match, which promotes the migration and separation of light-induced electrons and holes and increases both light absorbance and the specific surface area. This study introduces an effective and feasible strategy for improving the photocatalytic performances of COFs via subtly integrating TpPa-1 COFs with a ZnAgInS nanosphere into an organic-inorganic hybrid. The results of the photocatalytic experiments indicate that the fabricated hybrid has a potential application in the highly efficient removal of organic pollutants.

Construction of MOF/COF Hybrids for Boosting Sunlight-Induced Fenton-like Photocatalytic Removal of Organic Pollutants.

In this work, a metal-organic framework (MOF) material of NH2-MIL88B was hybridized with TpPa-1-COF through covalent bonding, and the hybrid was subsequently employed for the degradation of Rhodamine B (RhB) and tetracycline (TC) by simulated sunlight-induced Fenton-like exciting H2O2. The obtained results show that its photocatalytic activity is much better than those of its parent MOF and covalent organic framework (COF). Moreover, it is much higher than that of bare photocatalysis without Fenton-like excitation of H2O2. The high degradation efficiency is ascribed to two factors. One is the formation of hybrid, which promotes charge separation and light absorbance. Another is the Fenton-like excitation of H2O2, which produces more hydroxyl radicals (•OH). This report presents a facile approach to greatly improve the photocatalytic property of MOF materials by the formation of hybrid with COFs and Fenton-like excitation of H2O2.

Dehydration-Reaction-Based Low-Temperature Synthesis of Amorphous SnOx for High-Performance Perovskite Solar Cells.

The development of methodologies for synthesizing carrier-transporting materials is critical for optoelectronic device fabrication. Amorphous metal oxides have emerged as potential carrier transport materials for perovskite tandem solar cells and flexible electronics due to their ease of fabrication and excellent electronic properties. However, perovskite solar cells employing amorphous metal oxides as the electron-transporting layers (ETLs) remain inefficient. This research describes a moderate dehydration reaction for the low-temperature synthesis of amorphous SnOx. We investigated this amorphous SnOx as the ETL for perovskite solar cells and demonstrated a maximum power conversion efficiency (PCE) of 20.4%, the greatest efficiency ever attained with an amorphous metal oxide ETL produced below 100 °C. Remarkably, the device maintained 85% of its initial efficiency for more than 4800 h. Furthermore, flexible perovskite solar cells based on this amorphous SnOx have a maximum PCE of 11.7%. Finally, this amorphous SnOx was used to fabricate LEDs and exhibited a maximum external quantum efficiency of over 3%.

Fabrication of 2D-2D Heterojunction Catalyst with Covalent Organic Framework (COF) and MoS2 for Highly Efficient Photocatalytic Degradation of Organic Pollutants.

In this work, for the first time, we fabricated a novel covalent organic framework (COF)-based 2D-2D heterojunction composite MoS2/COF by a facile hydrothermal method. The results of photocatalytic degradation of TC and RhB under simulated solar light irradiation showed that the as-prepared composite exhibited outstanding catalytic efficiency compared with pristine COFs and MoS2. The significantly enhanced catalytic efficiency can be ascribed to the formation of 2D-2D heterojunction with a well-matched band position between COF and MoS2, which can effectively restrain the recombination of charge carriers and increase the light absorption as well as the specific surface area. Moreover, the fabricated 2D-2D layered structure can effectively increase the contact area with an intimate interface contact, which greatly facilitates the charge mobility and transfer in the interfaces. This study reveals that artful integration of organic (COFs) and inorganic materials into a single hybrid with a 2D-2D interface is an effective strategy to fabricate highly efficient photocatalysts.

Fabrication of Hierarchical Co9S8@ZnAgInS Heterostructured Cages for Highly Efficient Photocatalytic Hydrogen Generation and Pollutants Degradation.

In the present study, a hierarchical Co9S8@ZnAgInS heterostructural cage was developed for the first time which can photocatalytically produce hydrogen and degrade organic pollutants with high efficiency. First, the Co9S8 dodecahedron was synthesized using a metal-organic framework (MOFs) material, ZIF-67, as a precursor, then two kinds of metal sulfide semiconductors were elaborately integrated into a hierarchical hollow heterostructural cage with coupled heterogeneous shells and 2D nanosheet subunits. The artfully designed hollow heterostructural composite exhibited remarkable photocatalytic activity without using any cocatalysts, with a 9395.3 µmol g-1 h-1 H2 evolution rate and high degradation efficiency for RhB. The significantly enhanced photocatalytic activity can be attributed to the unique architecture and intimate-contact interface between Co9S8 and ZnAgInS, which promote the transfer and separation of the photogenerated charges, increase light absorption, and offer large surface area and active sites. This work presents a new strategy to design highly active semiconductor photocatalysts by using MOF materials as precursors and coupling of metal sulfide semiconductors to form hollow architecture dodecahedron cages with an intimate interface.

Highly Reversible Conversion Anodes Composed of Ultralarge Monolithic Grains with Seamless Intragranular Binder and Wiring Network.

Conversion anodes enable a high capacity for lithium-ion batteries due to more than one electron transfer. However, the collapse of the host structure during cycling would cause huge volume expansion and phase separation, leading to the degradation and disconnection of the mixed conductive network of the electrode. The initial nanostructuring and loose spatial distribution of active species are often resorted to in order to alleviate the evolution of the electrode morphology, but at the cost of the decrease of grain packing density. The utilization of ultralarge microsized grains of high density as the conversion anode is still highly challenging. Here, a proof-of-concept grain architecture characterized by endogenetic binder matrix and wiring network is proposed to guarantee the structural integrity of monolithic grains as large as 50-100 µm during deep conversion reaction. Such big grains were fabricated by self-assembly and pyrolysis of a Keggin-type polyoxometalate-based complex with protonated tris[2-(2-methoxyethoxy)-ethyl]amine (TDA-1-H+). The metal-organic precursor can guarantee the firm adherence of numerous Mo-O clusters and nuclei into a highly elastic monolithic structure without evident grain boundaries and intergranular voids. The pyrolyzed TDA-1-H+ not only serves as in situ binder and conductive wire to glue adjacent Mo-O moieties but also acts as a Li-ion pathway to promote sufficient lithiation on surrounding Mo-O. Such a monolithic electrode design leads to an unusual high-conversion-capacity performance (1000 mAh/g) with satisfactory reversibility (reaching at least 750 cycles at 1 A/g). These cycled grains are not disassembled even after undergoing long-term cycling. The conception of the intragranular binder is further confirmed by consolidating the MoO2 porous network after in situ stuffing of MoS2 nanobinders.

Stacking of Tailored Chalcogenide Nanosheets around MoO2-C Conductive Stakes Modulated by a Hybrid POM⊂MOF Precursor Template: Composite Conversion-Insertion Cathodes for Rechargeable Mg-Li Dual-Salt Batteries.

Mg anode has pronounced advantages in terms of high volumetric capacity, resource abundance, and dendrite-free electrochemical plating, which make rechargeable Mg-based batteries stand out as a representative next-generation energy storage system utilized in the field of large-scale stationary electric grid. However, sluggish Mg2+ diffusion in cathode lattices and facile passivation on the Mg anode hinder the commercialization of Mg batteries. Exploring a highly electroactive cathode prototype with hierarchical nanostructure and compatible electrolyte system with the capability of activating both an anode and a cathode is still a challenge. Here, we propose a POM⊂MOF (NENU-5) core-shell architecture as a hybrid precursor template to achieve the stacking of tailored chalcogenide nanosheets around MoO2-C conductive stakes, which can be employed as conversion-insertion cathodes (Cu1.96S-MoS2-MoO2 and Cu2Se-MoO2) for Mg-Li dual-salt batteries. Li-salt modulation further activates the capacity and rate performance at the cathode side by preferential Li-driven displacement reaction in Cu+ extrusible lattices. The heterogeneous conductive network and conformal dual-doped carbon coating enable a reversible capacity as high as 200 mAh/g with a coulombic efficiency close to 100%. The composite cathode can endure a long-term cycling up to 400 cycles and a high current density up to 2 A/g. The diversity of MOF-based materials infused by functional molecules or clusters would enrich the nanoengineering of electrodes to meet the performance demand for future multivalent batteries.

Improvement Photocatalytic Activity of P25 by Modification with a Rare Earth-Free Upconversion Nanocrystal.

It has been reported that coupling TiO2 with rare earth upconversion nanocrystals (UCNCs) is an efficient strategy to significantly improve photocatalytic activity of TiO2. However, the rare earth materials are scarcity and cost, and the synthesis process of UCNCs using the rare earth materials is complicated. In the present study, we have designed a new approach using a rare earth-free upconversion nanocrystal (REF-UCNCs) as upconversion luminescent material to replace the rare earth UCNCs. A novel nanocomposite photocatalyst of REF-UCNCs@P25: Mo/GN was developed for the first time. Based on the designed structure, the REF-UCNCs, Mo-doping, and GN (graphene) have a synergistic effect that can improve catalytic activity of P25 significantly. The results of photocatalytic experiments using RhB as a model pollutant under simulated solar light irradiation show that the photocatalytic efficiency of the as-prepared catalyst is 3-folds higher than that of benchmark substance P25. This work provides a new strategy for efficiently improving catalytic activity of semiconductor photocatalysts by coupling with REF-UCNCs. This approach is facile and low-cost which can be widely applied for modification of semiconductor photocatalysts and facilitates their applications in environmental protection issues using solar light.

Bioactivation of 1-chloro-2-hydroxy-3-butene, an in vitro metabolite of 1,3-butadiene, by rat liver microsomes.

1-Chloro-2-hydroxy-3-butene (CHB) is an in vitro metabolite of 1,3-butadiene, a rodent/human carcinogen. To search for an approach detecting CHB in vivo, it is vital to obtain a full understanding of CHB metabolism. Previously, we demonstrated that CHB was bioactivated to 1-chloro-3-buten-2-one (CBO) by alcohol dehydrogenase. However, CHB metabolism by cytochrome P450s has not been reported. Thus, in the present study, CHB metabolism by rat liver microsomes was investigated. The results showed that CHB was converted to 1-chloro-3,4-epoxy-2-butanol (CEB) and CBO. 4-Methylpyrazole, a cytochrome P450 2E1-specific inhibitor, inhibited the formation of both CEB and CBO, while 1-benzylimidazole, a generic cytochrome P450 inhibitor, completely abolished the formation of CEB and CBO, suggesting that CHB metabolism was mediated by cytochrome P450s. Because the molecules have two chiral centers, CEB was detected as two stereoisomers, which were designated D-CEB and M-CEB, and were characterized as (2S,3R)-/(2R,3S)-CEB and (2R,3R)-/(2S,3S)-CEB, respectively. The amounts of M-CEB were more than those of D-CEB by 50-80%. The amounts of CEB and CBO increased linearly over time from 10 (or 20 min for CBO) to 50 min. CHB metabolism followed Michaelis-Menten kinetics; the Km and Vmax values were determined to be 6.4 ±â€¯0.7 mM and 0.10 ±â€¯0.01 nmol/min/mg protein for D-CEB, 4.2 ±â€¯0.5 mM and 0.16 ±â€¯0.01 nmol/min/mg protein for M-CEB, and 4.0 ±â€¯0.5 mM and 4.6 ±â€¯0.5 nmol/min/mg protein for CBO, respectively. Thus, CBO was the dominant product of CHB metabolism. Moreover, CEB was genotoxic at ≥ 50 µM as evaluated by the comet assay. Collectively, the data showed that CHB could be bioactivated to CEB and CBO by cytochrome P450s with CBO being the predominant product. Thus, the formation of CEB and CBO can be used as evidence of CHB production. The products may also play a role in toxicity of CHB.

Large enhanced photocatalytic activity of g-C3N4 by fabrication of a nanocomposite with introducing upconversion nanocrystal and Ag nanoparticles.

A novel heterostructured nanocomposite UCNPs@SiO2@Ag/g-C3N4 was developed for the first time to substantially boost the solar-light driven photocatalytic activity of g-C3N4. Its photocatalytic properties and photocatalytic mechanism were investigated. The as-synthesized photocatalyst with excellent improvement in the solar absorption and separation efficiency of photoinduced electron-hole pairs exhibited optimum solar-induced photocatalytic activity in dye degradation and hydrogen production. The experimental results showed that the rates of degradation of Rhodamine B (RhB) and hydrogen evolution were about 10 and 12 times higher than that of pristine g-C3N4, respectively. The excellent photocatalytic activity was attributed to the synergetic effect of upconversion nanoparticles (UCNPs) and Ag nanoparticles (NPs) on the modification of the photocatalytic properties of g-C3N4, resulting in a broad light response range for g-C3N4 as well as the fast separation and slow recombination of photoinduced electron-hole pairs. This study provides new insight into the fabrication of g-C3N4-based nanocomposite photocatalysts with high catalytic efficiency through the artful assembly of UCNPs, Ag NPs and g-C3N4 into a hetero-composite nanostructure. The prominent improvement in photocatalytic activity enables the potential application of g-C3N4 in the photocatalytic degradation of organic pollutants and hydrogen production utilizing solar energy.

Huge enhancement of upconversion luminescence by dye/Nd3+ sensitization of quenching-shield sandwich structured upconversion nanocrystals under 808 nm excitation.

Lanthanide-doped upconversion nanoparticles (UCNPs) have shown potential applications in diverse fields. However, their upconversion luminescence (UCL) intensity and excitation wavelength range are limited by the weak and narrowband absorption of lanthanide ions. Herein, we introduce and validate a strategy to largely increase the absorptivity and upconversion luminescence intensity under 808 nm excitation by broadband dye-sensitized quenching-shield sandwich structured upconversion nanocrystals NaLuF4:Gd,Yb,Tm@NaLuF4:Gd,Yb@NaNdF4:Yb. The dye molecules anchored on the surface of the UCNPs serve as an antenna which can broadly and strongly harvest NIR light. The Nd3+ facilitates the energy transfer and photon upconversion of the lanthanide activator at a biocompatible excitation wavelength (around 800 nm) with a significant increase in penetration ability and minimizes the overheating problem associated with conventional 980 nm excitation. The quenching-shield sandwich structure can greatly eliminate the deleterious cross-relaxation pathway between the activator and sensitizer. This approach combines the merits of the use of Nd3+ as a sensitizer, a quenching-shield sandwich structure and the "antenna" effect, leading to a tremendous enhancement of UCL under excitation at 808 nm. These well-designed UCNPs excited at 808 nm with improved optical performances will outperform conventional UCNPs excited at 980 nm and play an important role in the development of luminescent probes for future biological and medical applications.

Improving Upconversion Luminescence by Coating Active Shell: A Case Study on NaYF4:Gd, Yb, Er@NaYF4:Yb, Pr.

Upconversion nanocrystals (UCNCs) have a lot of advantages over other fluorescent materials. However, their applications are still limited due to the relatively low upconversion luminescence (UCL). In the present study, a novel core/shell structural upconversion nanocrystal NaYF4:Gd, Yb, Er@NaYF4:Yb, Pr was prepared successfully with a facilely solvothermal method and the properties of the nanocrystal were investigated. It was interesting to find that the as-prepared nano-crystal showed excellent UCL. Its UCL intensity was 65, 44, and 20 times higher than those of core nanocrystal NaYF4:Gd, Yb, Er, core/inert-shell nanocrystal NaYF4:Gd, Yb, Er@NaYF4, and core/active-shell nanocrystal NaYF4:Gd, Yb, Er@NaYF4:Yb, respectively. Moreover, the measured UCL lifetime of the as-prepared nanocrystal was longer than those of the controls. The mechanism of the UCL enhancement of the product was discussed in detail. The high UCL of the as-prepared product could be ascribed to the function of the shell, energy transfer from the active shell to the core, and Pr³âº-doping in the shell. This study provided a new insight into the fabrication of core­ shell structural upconversion nanocrystals with high UCL. The high UCL potentially increases the overall upconversion nanocrystal detectability for highly sensitive biological, medical, and optical detections.

Facile synthesis of hierarchical Mn3O4 superstructures and efficient catalytic performance.

The development of novel materials with excellent performance depends not only on the constituents but also on their remarkable micro/nanostructures. In this work, manganese oxide (Mn3O4) hausmannite structures with a uniform three-dimensional (3D) flower-like hierarchical architecture have been successfully synthesized by a novel chemical route using surfactants as structure-directing agents. Microstructure analysis indicates that the obtained 3D flower-like Mn3O4 superstructure consists of a large number of two-dimensional (2D) Mn3O4 nanosheets, which is different from the reported 3D Mn3O4 hierarchical structures based on zero-dimensional nanoparticles or one-dimensional nanowires and nanorods. This 3D Mn3O4 hierarchical architecture provides us with another type of manganese oxide with different superstructural characteristics, which may have potential practical applications in the catalytic degradation of organic pollutants. The catalytic performance of this hierarchical Mn3O4 superstructure, which was prepared by three different types of structure-directing agents, including cetyltrimethylammonium bromide (CTAB), poly(vinylpyrrolidone) (PVP), and poly(ethylene oxide)-poly(propylene oxide) (P123), was evaluated for the catalytic degradation of organic pollutants, e.g. methylene blue. Interestingly, the hierarchical Mn3O4 superstructure prepared using CTAB as a template showed efficient catalytic degradation. The formation processes and possible growth mechanism of this novel 3D Mn3O4 hierarchical superstructure assembled by 2D Mn3O4 nanosheets are discussed in detail.

Huge enhancement of upconversion luminescence by broadband dye sensitization of core/shell nanocrystals.

Upconversion nanocrystals (UCNCs) hold promise for bioimaging, solar cells, photocatalysis and volumetric displays. However, their upconversion luminescence intensities are usually low due to the weak and narrowband near-infrared absorption of lanthanide ions. Herein, we introduce and validate a strategy to hugely enhance upconversion luminescence intensity by using an organic near-infrared dye as an antenna to sensitize core/shell UCNCs. The dye can increase absorptivity and broaden the absorption spectrum of the UCNCs. Such dye sensitization, in combination with a core/shell structure, can tremendously enhance the upconversion luminescence (UCL) intensity of the UCNCs. The UCL intensity of dye-sensitized UCNCs excited at 820 nm is 800-folds higher than that of pure UCNCs excited at 980 nm. Further enhancement can be obtained by optimization of the dye emission and UCNC absorption spectral overlap. Moreover, the proposed approach can be extended to cover any part of the solar spectrum by using a set of dyes. This work provides new insights into the efficient enhancement of upconversion luminescence of the UCNCs and facilitates their applications.

Preparation of a novel nanocomposite NaLuF4:Gd,Yb,Tm@SiO2@Ag@TiO2 with high photocatalytic activity driven by simulated solar light.

A novel nanocomposite photocatalyst NaLuF4:Gd,Yb,Tm@SiO2@Ag@TiO2 was developed for the first time. This composite material has a sandwich structure, including a NaLuF4:Gd,Yb,Tm upconversion nanocrystals (UCNCs) core, a media shell of amorphous SiO2 decorated with Ag nanoparticles, and an outer shell of anatase TiO2. The designed new structure takes advantage of the synergetic effect of UCNCs, Ag nanoparticles and TiO2. The UCNCs absorb near-infrared (NIR) light and transfer energy to TiO2, which extends the light responsive range of TiO2 to the NIR region. Ag nanoparticles not only enhance upconversion luminescence of the UCNCs but also enhance light harvesting and improve charge separation of TiO2. The results of photocatalytic applications show that the as-prepared catalyst has high photocatalytic activity. This study provides new insights into the fabrication of TiO2-based nanocomposite photocatalysts with high catalytic efficiency through effective integration of upconversion material, noble metal and TiO2 into a hetero-composite nanostructure.

Recent Advances of NaLuF4-Based Upconversion Nanocrystals.

In recent years, lanthanide-doped upconversion nanocrystals have been developed as a new class of fluorescent probe that have become promising alternatives to organic fluorophores and quantum dots for applications in biological and medical fields. This technique offers large anti-Stokes shifts, low autofluorescence background, sharp emission bandwidths, high photochemical stability, and deep penetration depth. According to the recently reports, NaLuF4 is a better host material for lanthanide upconversion compared to the classic NaYF4 host. Some reviews concerning the upconversion nanocrystals have been reported, but no one focuses on the NaLuF4-based nanocrystals. In this review, recent reports regarding the synthesis of NaLuF4-based nanocrystals and their upconversion luminescence properties, surface modification, and biological applications are summarized.

Preparation of Novel Europium Complex Doped Ag@SiO2 Nanoparticles with Intense Fluorescence.

In this study, a new europium complex of 4,4'-bis (1",1",1",2",2",3",3"-heptafluoro-4",6"- hexanedion-6"-yl)-o-terpheny-Eu(3+)-4,7-diphenyl-1,10-phenanthroline-2,9-dicarboxylic acid-(3-aminopropyl) trimethoxysilane (BHHT-Eu(3+)-DPPDA-APTMS) was prepared first. Then novel core-shell Ag@SiO2 nanoparticles with BHHT-Eu(3+)-DPPDA-APTMS doped in shell were synthesized by a facile water-in-oil microemulsion method. The properties of the prepared complex and nanoparticles, and the effect of metal enhanced fluorescence for the nanoparticles were investigated. The prepared nanopartilces exhibited intense fluorescence, uniform morphology and good water-solubility. The fluorescent intensities of silver core-present nanopartciles were significant higher than that of silver core-absent nanoparticles owing to the metal enhanced fluorescence of silver core. It is expectable that the as-prepared nanoparticles can serve as a potential fluorescent nanoprobe, applying in high sensitive biological and medical detections.

Synthesis of NaYF4 and NaLuF4 Based Upconversion Nanocrystals and Comparison of Their Properties.

In this study, four kinds of upconversion nanocrystals (UCNs) have been successfully synthesized by a facile solvothermal method. The morphology, crystalline phase, composition, grain size, upconversion luminescence and cell image of the UCNs were investigated. The properties of the NaLuF4-based UCNs were compared with the counterparts of NaYF4-based UCNs. It is found that the NaLuF4-based UCNs are apt to form hexagonal phase structures, while NaYF4-based UCNs of NaYF4:Yb, Er and NaYF4:Gd, Yb, Er are cubic and hexagonal phases respectively. The upconversion emission intensities of the NaLuF4-based UCNs are higher than that of NaYF4-based UCNs, and Gd3+ presented UCNs are higher than that of Gd3+ absented UCNs. The bioimaging application of NaLuF4:Gd, Yb, Er shows that bright upconversion luminescence can be observed when UCNs-labeled HeLa cells are excited with 980 nm light.