Multi-functional ratiometric detection based on dual-emitting N-doped carbon dots.

Ratiometric fluorescence probes based on multi-emission carbon dots improve accuracy and sensitivity on detecting various environment issues. Herein, a novel dual-emitting N-doped carbon dots (N-CDs) was synthesized from citric acid and urea via a solvothermal method in N,N-dimethylformamide (DMF). The blue and orange emissions of N-CDs in water were modulated, and pure white light-emitting with Commission Internationale de L'Eclairage (CIE) coordinates of (0.33, 0.33) was achieved. The two PL centers behaved differently for Fe3+, Cu2+ and Ag+ ions, with the limit of detection (LOD) of ppm as fluorescence probes. Additionally, N-CDs displayed unique solvatochromism phenomenon. A new green emission appeared in organic solvents and gradually quenched with the increase of solvent polarity. The ratiometric PL displayed an excellent linear response for detecting water, and the LOD was between 0.003 % and 0.3 % in DMF, ethanol, isopropanol and N-methylpyrrolidone. Furthermore, N-CDs exhibited pH-sensitive response in the range of 4.0-7.0 and temperature-dependent response during heating-cooling cycles between 15 and 70 °C. A simple, efficient and reliable multi-functional ratiometric probe for detecting metal ions, water content, pH and temperature simultaneously was realized. However, there is a need for future application research to overcome the limitation imposed by the excitation wavelength of 330 nm.

Heating-free synthesis of red emissive carbon dots through separated processes of polymerization and carbonization.

Polymerization and carbonization are believed as two basic processes for the bottom-up synthesis of carbon dots (CDs). Since these two processes usually occur simultaneously due to the high reaction temperature and fast reaction rate, it is still a challenge to separate and control these two processes. In the present work, we reported a new room temperature method, which achieved the separated and controlled polymerization and carbonization processes. The polymerization process is realized by dissolving o-phenylenediamine (OPD) in ethanol at room temperature, and finally obtained polymer dots (PDs) without any lattice with a sphere size of 29.6 nm. The carbonization process begins in a manual way by adding concentrated sulfuric acid. After carbonization, CDs (noted as CPDs in this work) with a size of 3.6 nm and a clear lattice can be obtained. Importantly, the separated polymerization and carbonization make us possible to adjust the composition or interactions of intermediate products during the synthesis process. As a prototype, we added acetic acid (AA) additives into OPD precursors during the polymerization stage. Due to the crosslink enhanced emission (CEE) effect via hydrogen bonds which are produced by the amide groups from AA reaction products with H in the -NH3+ or aromatic ring, the resulted CPDs show improved PLQY from an initial 6.87% (without AA) to 16.47%. The current work realized the separated and controllable polymerization and carbonization processes, opening up the door for tuning the composition and interactions of intermediate products before carbonization.

Lead-Free Copper-Based Perovskite Nanonets for Deep Ultraviolet Photodetectors with High Stability and Better Performance.

Considering practical application and commercialization, the research of non-toxic and stable halide perovskite and its application in the field of photoelectric detection have received great attention. However, there are relatively few studies on deep ultraviolet photodetectors, and the perovskite films prepared by traditional spin-coating method have disadvantages such as uneven grain size and irregular agglomeration, which limit their device performance. Herein, uniform and ordered Cs3Cu2I5 nanonet arrays are fabricated based on monolayer colloidal crystal (MCC) templates prepared with 1 µm polystyrene (PS) spheres, which enhance light-harvesting ability. Furthermore, the performance of the lateral photodetector (PD) is significantly enhanced when using Cs3Cu2I5 nanonet compared to the pure Cs3Cu2I5 film. Under deep ultraviolet light, the Cs3Cu2I5 nanonet PD exhibits a high light responsivity of 1.66 AW-1 and a high detection up to 2.48 × 1012 Jones. Meanwhile, the unencapsulated PD has almost no response to light above 330 nm and shows remarkable stability. The above results prove that Cs3Cu2I5 nanonet can be a great potential light-absorbing layer for solar-blind deep ultraviolet PD, which can be used as light absorption layer of UV solar cell.

Sandwich-type CoSe2-CNWs@rGO/S composites with efficient trapping and catalytic conversion of polysulfides in lithium-sulfur batteries.

Although lithium-sulfur batteries (LSBs) are very promising in energy storage devices, their low conductivity, shuttle effect, and volume expansion unfavorably lead to sluggish kinetics and worsening electrochemical performance. To address these problems, we firstly prepared conductive carbon nanowires embedded with lithiophilic CoSe2 nanoparticles (CoSe2-CNWs), and utilized CoSe2-CNWs to construct reduced graphene oxide (rGO) sheets; thereby, sandwich-type CoSe2-CNWs@rGO composites were assembled. CoSe2-CNWs@rGO composites were taken as the sulfur host. Due to the alternating rGO sheets and active sulfur, the special sandwich structure can maximize the use of sulfur, confine polysulfides physically, favor electron transport, and cushion the volume change during cycling. The interlayer CoSe2-CNWs network also can entrap polysulfides chemically, promote the electron transfer, and improve the reaction kinetics, owing to the synergetic merits of high polarity and conductivity. Compared with CoSe2-CNWs/S and Co-CNWs/S, the CoSe2-CNWs@rGO/S cathode shows a significant improvement in cell performance. Its specific capacity decreases from 1137.9 mA h g-1 at 0.1 C to 649.7 mA h g-1 at 2 C, demonstrating the optimal rate performance. The cycling capacity also slowly reduces from 975.4 mA h g-1 to 839.7 mA h g-1 after 150 cycles at 0.5 C, showing a high retention of 86.1% with a tiny average fading rate (0.093%).

Employing synergetic effect of ZnSe quantum dots and layered Ni(OH)2to boost the performance of lithium-sulfur cathodes.

The low sulfur utilization, cycling instability, and sluggish kinetics are the critical obstructions to practical applications of lithium-sulfur batteries (LSBs). Constructing sulfur hosts with high conductivity, suppressed shuttle effect, and rapid kinetics is essential for their practical application in LSBs. Here, we synthetically utilized the merits of ZnSe quantum dots (QDs) and layered Ni(OH)2to boost the performance of LSBs. A novel core-shell ZnSe-CNTs/S@Ni(OH)2was constructed using the ZnSe-CNTs network as framework to load sulfur and following with Ni(OH)2encapsulation. The CNT network decorated with ZnSe QDs not only serves as a conductive framework providing fast electron/ion transfer channels, but also limits polysulfide diffusion physically and chemically. Layered Ni(OH)2, the wrinkled encapsulation, not only permits fast electron/ion transfer, but also buffers the expansion, confines active materials, and limits the polysulfide dissolution chemically. When used as a cathode, ZnSe-CNTs/S@Ni(OH)2presents enhanced electrochemistry performance compared with ZnSe-CNTs/S and CNTs/S. The average specific capacity decreases from 1021.9 mAh g-1at 0.2 C to 665.0 mAh g-1at 2 C, showing rate capacity much higher than ZnSe-CNTs/S and CNTs/S. After 150 cycles, the capacity at 0.5 C slowly reduces from 926.7 to 789.0 mAh g-1, showing high retention of 85.1%. Therefore, our investigation provides a new strategy to construct a promising sulfur cathode for LSBs.

Bi and Sb Codoped Cs2Ag0.1Na0.9InCl6 Double Perovskite with Excitation-Wavelength-Dependent Dual-Emission for Anti-Counterfeiting Application.

The growing demands for optical anti-counterfeiting technology require the development of new environmentally friendly materials with single component, multimodal fluorescence and high stability. Herein, the Bi/Sb codoped Cs2Ag0.1Na0.9InCl6 lead-free double perovskite material is reported as an efficient multimodal luminescence material with excitation-wavelength-dependent emission. When excited by 360 nm UV light, dual-emission is observed at 455 and 560 nm, which comes from the 3P1-1S0 transition of Sb3+ ions and self-trapped excitons (STEs), respectively. Under the 320 nm UV lamp, the microcrystals show only a blue emission centered at 455 nm. Therefore, the Bi/Sb codoped Cs2Ag0.1Na0.9InCl6 double perovskite emits blue and yellow lights under the 320 and 360 nm UV lamp, respectively. Moreover, the obtained double perovskite shows a high PLQY up to 41% and excellent stability against both air and high temperature, which make it a promising anti-counterfeiting material.

A special core-shell ZnS-CNTs/S@NH cathode constructed to elevate electrochemical performances of lithium-sulfur batteries.

Lithium-sulfur batteries (LSBs) are regarded as promising candidates for next-generation electrochemical energy storage systems due to their low cost and high energy density. However, the insulative sulfur, the volume expansion and high soluble polysulfides are three roots impeding their practical applications, and consequently bring challenges of low sulfur utilization, poor cyclic stability and sluggish redox kinetics. Herein, a special core-shell ZnS-CNTs/S@Ni(OH)2 (labeled as ZnS-CNTs/S@NH) cathode has been designed to overcome above obstacles and elevate the electrochemical performance. The ZnS-CNTs/S@NH cathode is synthesized via a facile step-by-step strategy, in which ZnS-decorated CNTs was used as a framework to load sulfur and followed with a ultrathin Ni(OH)2 (NH) layer encapsulation. The ZnS-CNT core combines merits of CNT network and polar ZnS quantum dots (QDs), accommodating the volume change, offering efficient pathways for fast electron/ion transport, and anchoring polysulfides through polar interactions. The outer Ni(OH)2 shell physically confines the active material and meanwhile provides plenty of catalytic sites for effective polysulfide chemisorption. Benefiting from these merits, the ZnS-CNTs/S@NH cathode exhibits excellent cell performances in comparison with ZnS-CNTs/S and CNTs/S. Its discharge capacity at different C-rates is optimal in the three cathodes, which decreases from 1037.0 mAh g-1 at 0.1 C to 646.1 mAh g-1 at 2.0 C. Its cyclic capacity also manifests the slowest reduction from 861.1 to 760.1 mAh g-1 after 150 cycles at 0.5 C, showing a high retention (88.3%) and a tiny average fading rate (0.078%). The strategy in this work provides a feasible approach to design and construct core-shell cathode materials for realizing practically usable Li-S batteries.

Precise control of the ratiometric fluorescence of dual-emissive B/N-doped carbon dots using pH-dependent bonds.

Precise control of the structure and bonds of doped carbon dots (CDs) is important, so that their fluorescence can be tuned as desired. Up until now, there has been a lack of effective ways to control the bonds of doped CDs. In this article, we show that the fluorescence of B/N-doped carbon dots (B/N-CDs) can be precisely tuned just by controlling their precursors' pH values. The prepared B/N-CDs exhibit two emission bands, including one emission peak at around 450 nm due to the defect state caused by low sp2 hybridization of carbon atoms, as well as another emission peak at around 360 nm caused by the B-N bond. The results for the ratio of the maximum intensity of the two emission peaks above show a linear relationship. Meanwhile, the role of the pH value of the precursors on the luminescence of B/N-CDs is deeply studied. On the one hand, the pH value affects the bonding process of CDs. N-H bonds tend to form at a low pH value, while more competitive B-N bonds exist at much higher pH value, leading to the pH-dependent intensity of the 360 nm emission band. On the other hand, a high pH value causes higher crystallinity, thus suppressing defect-state fluorescence at 450 nm. The dual effects of pH lead to precisely controlled dual-emission intensities as well as ratiometric fluorescence.

Incorporation ZnS quantum dots into carbon nanotubes for high-performance lithium-sulfur batteries.

Constructing sulfur hosts with high electronic conductivity, large void space, strong chemisorption, and rapid redox kinetics is critically important for their practical applications in lithium-sulfur batteries (LSBs). Herein, by coupling ZnS quantum dots (QDs) with carbon nanotubes (CNTs), one multifunctional sulfur host CNT/ZnS-QDs is designed via a facile one-step hydrothermal method. SEM and TEM analyses reveal that small ZnS-QDs (<5 nm) are uniformly anchored on the CNT surface as well as encapsulated into CNT channels. This special architecture ensures sulfur direct contacting with highly conductive CNTs; meanwhile, the catalytic effect of anchored ZnS-QDs improves the chemisorption and confinement to polysulfides. Benefiting from these merits, when used as sulfur hosts, this special architecture manifests a high specific capacity, superior rate capability, and long-term cycling stability. The ZnS-QDs dependent electrochemical performance is also evaluated by adjusting the mass ratio of ZnS-QDs, and the host of CNT/ZnS-QDs 27% owns the optimal cell performance. The specific capacity decreases from 1051 mAh g-1 at 0.2 C to 544 mAh g-1 at 2.0 C, showing rate capability much higher than CNT/S and other CNT/ZnS-QDs/S samples. After 150 cycles, the cyclic capacity at 0.5 C exhibits a slow reduction from 1051 mAh g-1 to 771 mAh g-1, showing a high retention of 73.4% with a coulombic efficiency of over 99%. The electrochemical impedance spectroscopy analyses demonstrate that this special architecture juggles high conductivity and excellent confinement of polysulfides, which can significantly suppress the notorious shuttle effect and accelerate the redox kinetics. The strategy in this study provides a feasible approach to design efficient sulfur hosts for realizing practically usable LSBs.

Improving power conversion efficiency in luminescent solar concentrators using nanoparticle fluorescence and scattering.

Large-size luminescent solar concentrators (LSCs), which act as a complement to silicon-based photovoltaic (Si-PV) systems, still suffer from low power conversion efficiency (PCE). How to improve the performance of LSCs, especially large ones, is currently a hot research topic. Traditional LSCs have only a single transmission mode of fluorescence from the luminescent materials to the Si-PV, but here we introduce a new idea to improve the absorption of Si-PV by employing dual transmission modes of both fluorescence and scattering light. To prepare LSCs with dual mode transmission, Si-PV systems are coupled around the edges of a light-harvesting slice, which is prepared by ultraviolet light-induced polymerization of methyl methacrylate (MMA) solution containing both luminescent CsPbBr3 and TiO2 nanocrystals (NCs). When the sun light or incident light is coupled into the light-harvesting slice, CsPbBr3 NCs can convert the incident light into fluorescence, and then partly transmit to Si-PV at the edges, where the light is finally converted into electrical energy. Besides the traditional fluorescence transmission mode, the addition of TiO2 brings another transmission mode, namely the scattering of incident light to Si-PV, leading to an increase in PCE. In comparison to that of pure CsPbBr3-based LSCs without the addition of TiO2 (0.97%), the PCE of TiO2-doped LSCs with a large size of 20 cm × 20 cm is improved to 1.82%. The maximal PCE appears for LSCs with a size of 5 cm × 5 cm, reaching 2.62%. The reported method of dual transmission modes is a new alternative way to improve the performance of LSC devices, which does not need to change the optical properties of luminescent materials. Moreover, the production process is simple, low-cost and suitable for preparing large area LSCs, further promoting the application of LSCs.

Self-Assembled Vanadium Oxide Nanoflakes for p-Type Ammonia Sensors at Room Temperature.

VO2(B), VO2(M), and V2O5 are the most famous compounds in the vanadium oxide family. Here, their gas-sensing properties were investigated and compared. VO2(B) nanoflakes were first self-assembled via a hydrothermal method, and then VO2(M) and V2O5 nanoflakes were obtained after a heat-phase transformation in nitrogen and air, respectively. Their microstructures were evaluated using X-ray diffraction and scanning and transmission electron microscopies, respectively. Gas sensing measurements indicated that VO2(M) nanoflakes were gas-insensitive, while both VO2(B) and V2O5 nanoflakes were highly selective to ammonia at room temperature. As ammonia sensors, both VO2(B) and V2O5 nanoflakes showed abnormal p-type sensing characteristics, although vanadium oxides are generally considered as n-type semiconductors. Moreover, V2O5 nanoflakes exhibited superior ammonia sensing performance compared to VO2(B) nanoflakes, with one order of magnitude higher sensitivity, a shorter response time of 14⁻22 s, and a shorter recovery time of 14⁻20 s. These characteristics showed the excellent potential of V2O5 nanostructures as ammonia sensors.

Dendrimer ligands-capped CH3NH3PbBr3 perovskite nanocrystals with delayed halide exchange and record stability against both moisture and water.

CH3NH3PbBr3 perovskite nanocrystals (NCs) suffer from poor stability because of their high sensitivity to environmental moisture and water. To solve this problem, previous works mainly focus on embedding perovskite NCs into water-resistant matrix to form large composites (size of microns or larger). As an alternative solution without serious changing of NC size, enhancing the stability of perovskite NCs themselves by ligand engineering is rarely reported. In this work, we used hyperbranched polyamidoamine (PAMAM) dendrimers with two different generations (G0 and G4) to synthesize CH3NH3PbBr3 perovskite NCs with high photoluminescence (PL) quantum yields (QY) above 70% and a new record stability. A novel dendrimers generation-dependent stability of perovskite NCs was observed. The water-resistance time is 18 h (27 h) for perovskite NCs capped by G0 (G4) generation of PAMAM, which is 7 times (11 times) longer than that of traditional oleic acid-capped NCs. Similar PAMAM generation-related stability is also observed in moisture-resistance tests. The stability time against moisture is 500 h (800 h) for G0 (G4) generation of PAMAM-capped perovskite NCs, which is a new record stability time against moisture for CH3NH3PbBr3 perovskite NCs. In addition, our results also indicate that PAMAM ligands outside perovskite NCs can dramatically slow down the speed of halide exchange. Even for the mixture of perovskite NCs with two different halide composition, the original luminescence properties of PAMAM-capped perovskite NCs can retain after mixing. In view of slow halide exchange speed, excellent water and moisture stability, PAMAM dendrimers-capped perovskite NCs and their mixture are available as color conversion single layer in fabrication of light-emitting diodes (LED).

Single component Mn-doped perovskite-related CsPb2ClxBr5-x nanoplatelets with a record white light quantum yield of 49%: a new single layer color conversion material for light-emitting diodes.

Single component nanocrystals (NCs) with white fluorescence are promising single layer color conversion media for white light-emitting diodes (LED) because the undesirable changes of chromaticity coordinates for the mixture of blue, green and red emitting NCs can be avoided. However, their practical applications have been hindered by the relative low photoluminescence (PL) quantum yield (QY) for traditional semiconductor NCs. Though Mn-doped perovskite nanocube is a potential candidate, it has been unable to realize a white-light emission to date. In this work, the synthesis of Mn-doped 2D perovskite-related CsPb2ClxBr5-x nanoplatelets with a pure white emission from a single component is reported. Unlike Mn-doped perovskite nanocubes with insufficient energy transfer efficiency, the current reported Mn-doped 2D perovskite-related CsPb2ClxBr5-x nanoplatelets show a 10 times higher energy transfer efficiency from perovskite to Mn impurities at the required emission wavelengths (about 450 nm for perovskite emission and 580 nm for Mn emission). As a result, the Mn/perovskite dual emission intensity ratio surprisingly elevates from less than 0.25 in case of Mn-doped nanocubes to 0.99 in the current Mn-doped CsPb2ClxBr5-x nanoplatelets, giving rise to a pure white light emission with Commission Internationale de l'Eclairage (CIE) color coordinates of (0.35, 0.32). More importantly, the highest PL QY for Mn-doped perovskite-related CsPb2ClxBr5-x nanoplatelets is up to 49%, which is a new record for white-emitting nanocrystals with single component. These highly luminescent nanoplatelets can be blended with polystyrene (PS) without changing the white light emission but dramatically improving perovskite stability. The perovskite-PS composites are available not only as a good solution processable coating material for assembling LED, but also as a superior conversion material for achieving white light LED with a single conversion layer.

Fast doping of Cu into ZnSe NCs by hydrazine promoted cation exchange in aqueous solution at room temperature.

Controllable doping is an effective way of tuning the properties of semiconductor nanocrystals (NCs). In this work, a simple strategy of fast doping Cu ions into ZnSe NCs under ambient conditions was proposed. The principle of doping is based on hydrazine (N2H4) promoted cation exchange reaction. By direct addition of Cu ion stock solution into the preformed ZnSe NCs, Cu doped ZnSe NCs can be obtained. Furthermore, the emission of doped NCs can be tuned by changing the amount of impurity ion addition. The cation exchange reaction is facilitated by three factors: 1) N2H4 addition, 2) fast impurity ions, and 3) partial stabilizer removal. The proposed cation exchange reaction in aqueous solution could be an alternate route for NC doping as well as synthesis of ionic NCs.

Hydrazine-promoted sequential cation exchange: a novel synthesis method for doped ternary semiconductor nanocrystals with tunable emission.

Using ZnSe nanocrystals (NCs) as starting material, Ag-doped or Cu-doped ZnCdSe ternary NCs were prepared by hydrazine-promoted sequential cation exchange in aqueous media. The composition of the NCs can be flexibly controlled by varying the amount of intermediate Ag or Cu cation addition, thus changing the emission of the ternary NCs while preserving the NC size. According to Vegard's law, the as-prepared ternary NCs possess an alloyed structure. In addition, the ternary NCs obtained have a high quantum yield, strong stability and a broad optical tuning range.

One-pot synthesis of multicolor MnSe:ZnSe nanocrystals for optical coding.

Though the investigation on controlling the fluorescence properties of nanocrystals (NCs) with single emission has been widely reported, few efforts were spent on adjusting the fluorescence properties of NCs with multiple emission peaks. In this work, we successfully synthesized multicolor MnSe:ZnSe NCs with multiple emission peaks and developed a simple and accurate method to realize photoluminescence (PL) spectra (or color) adjustment. The PL of MnSe:ZnSe NCs has two distinct emission peaks, the trap emission of ZnSe at 475nm and Mn(2+)-induced emission at 585nm. By adjusting the nucleation temperature, the emission color of the NCs can be encoded according to the ratio of the emission intensities at 475 and 585nm. With the nucleation temperature rising from 0 to 70°C, the PL ratio between trap emission and Mn(2+)-induced emission can be consecutively changed from (1, 3) to (1, 0.5). In addition, the trap state is deeply inside the NCs rather than on NCs surface so that the trap emission is stable during environment change. Thus, these MnSe:ZnSe NCs hold great promise as novel single-particle coding labels for biomedical imaging.

Automatically purification of aqueous CdTe nanocrystals in water-ethanol co-environment.

Purification is a separated post-treatment step after the synthesis of nanocrystals (NCs) in order to exclude excess ligands and monomers in NC solution. The common purification process involves many manipulations, such as concentrating, addition of anti-solvents and centrifugation, which are troublesome and time consuming. In this work, we originally integrate NC synthesis and NC purification in one-pot via selecting water-ethanol co-environment for NC synthesis and NC purification. Our research shows that NCs can grow in water-ethanol mixture. When growing into critical size, NCs will automatically precipitate from the solution. Element analysis demonstrates that precipitates fraction fits well with stoichiometric of ligand-capped NCs. Excess monomers are left in supernatant, and thus achieving automatically purification of NCs in the water-ethanol co-environment. By adjusting the volume ratios of water and ethanol in bi-solvent system, different-sized purified NCs can be controlled. Besides, this water-ethanol co-environment can be used in both thermal-promoted and hydrazine-promoted growth.

A facile method for gold decoration of Te@CdTe nanorods in aqueous solution.

Colloidal synthesis of metal-semiconductor hybrid nanostructures is mainly achieved in organic solution. In some applications of hybrid nanoparticles relevant in aqueous media, phase transfer of hydrophobic metal-semiconductor hybrid nanostructures is essential. In this work, we present a simple method for direct synthesis of water-soluble gold (Au) decorated Te@CdTe hybrid nanorods (NRs) at room temperature by using aqueous Te@CdTe NRs as templates, which were preformed by using CdTe nanocrystals (NCs) as precursor in the presence of hydrazine hydrate (N(2)H(4)). Our results showed that NRs were decorated with Au islands both on tips and along the surface of the NRs. The size and density of Au islands can be controlled by varying the amount of Au precursor (mixture of HAuCl(4) and thioglycolic acid (TGA)) and TGA/HAuCl(4) ratio. A possible growth mechanism for the Au decoration of Te@CdTe NRs is concluded as three steps: (1) the formation of AuTe(1.7) via the substitution reaction of Cd(2+) by Au(3+), (2) adsorption of Au-TGA complex onto the preformed AuTe(1.7) anchors and following reduction by CdTe and N(2)H(4), leading to the formation of small Au NCs, (3) Au NCs grow to bigger ones, followed by reduction of more Au precursor by N(2)H(4).

Microwave-assisted synthesis of fluorescent Ag nanoclusters in aqueous solution.

Fluorescent Ag nanoclusters are of significant interest because they provide the bridge between atomic and nanoparticle behavior in noble metals. Herein, microwave irradiation was originally used for the synthesis of water-soluble fluorescent Ag nanoclusters. As-prepared Ag nanoclusters present red fluorescence emission around 608 nm and a characteristic absorption peak at about 508 nm. Transmission electron microscopy (TEM) shows an average size of 1.6 nm for Ag nanoclusters. The effect of solution pH on the synthesis process and optical properties of Ag nanoclusters was investigated. The pH-dependent present form and adsorption capacity of poly(methacrylic acid, sodium salt) (PMAA) ligands are believed to be the reason for the pH effect.

Aqueous synthesis of internally doped Cu:ZnSe/ZnS core-shell nanocrystals with good stability.

To prepare biologically available Zn-based NCs in aqueous solution, we herein reported the synthesis of aqueous Cu:ZnSe/ZnS NCs with internally doped aqueous Cu:ZnSe NCs as the core template. Due to the dual protection of Cu impurities by the ZnSe core and ZnS shells, the as-prepared Cu:ZnSe/ZnS NCs show excellent stability in the open air, which overcomes the intrinsic instability of traditional aqueous Cu:ZnSe NCs. The as-prepared Cu:ZnSe/ZnS NCs possess extremely good stability, good biocompatibility and lower cytotoxicity, and thus can be used as a promising candidate for fluorescent NC-based biological applications.