Ternary alloyed Cu2–xSySe1–y nanocrystals (NCs) were synthesized by using a simple and phosphine-free colloidal approach, in which sulfur powder and 1-dodecanethiol (DDT) were used as sulfur sources. In both cases, the crystal phase transformed from cubic berzelianite to monoclinic djurleite structure together with the morphology evolution from quasi-triangular to spherical or discal with an increase of sulfur content. Accordingly, the near-infrared (NIR) localized surface plasmon resonance (LSPR) absorption of the as-obtained sulfur-rich NCs exhibited obvious red-shift of wavelength and widening of absorption width. When the sulfur powder was chosen as sulfur sources, the LSPR wavelength of the as-obtained alloyed Cu2–xSySe1–y NCs could be tuned from 975 to 1230 nm with a decrease of selenium content in the NCs. In contrast, the region of the red-shift could be up to 1250 nm for the alloyed NCs synthesized by incorporation of different DDT dosage into the reaction system. The different sulfur sources and the electron donating effects of the DDT as a ligand played an important role in the LSPR absorption tuning. This deduction could be testified by the post-treating the quasi-triangular Cu2–xSe NCs with DDT under different temperatures and over different reaction time, which exhibited a red-shift of LSPR wavelength up to 450 nm due to coordination of DDT to Cu atoms on the NC surface while incorporating some sulfur anions into the lattice. This study offers a convenient tool for tuning the LSPR absorption of copper chalcogenide NCs and makes them for application in biological and optoelectronic fields.

•White light-emitting diodes were fabricated based on cadmium-free Cu-In-Zn-S-based QDs and polymer via a simple solution-processed technique.•White electroluminescence was obtained under the annealing temperature of 95 °C.•The WLEDs exhibited a high CRI of 90 with a CIE coordinate of (0.33, 0.32).Bright white light-emitting diodes (WLEDs) were fabricated by using a simple solution-processed technique, in which the yellow cadmium-free Cu-In-Zn-S/ZnS core/shell quantum dots (QDs) blending with poly [(9, 9-dioctylfluorenyl-2, 7-diyl)-co-(4, 4′-(N-(p-butylphenyl)) diphenylamine)] (TFB) was used as emissive layers. The color of the electroluminescence (EL) from the device could be tuned from blue-green to white by varying the thermal annealing temperatures, and white EL emission could be obtained under the annealing temperature of 95 °C. A high color rendering index (CRI) of 90 and the Commission Internationale de l'Eclairage (CIE) color coordinates of (0.33, 0.32) were achieved in the WLEDs annealed at 95 °C, respectively. The WLEDs exhibited a low turn-on voltage of 2.5 V and a maximum luminance of 1500 cd/m2, which were maintained at 0.1 cd/A over a wide range of luminance from 100 to 1300 cd/m2. This work may open up a new way to realize white light in the planar WLEDs based on the cadmium-free QDs.Download high-res image (229KB)Download full-size image

As most heavy metals are highly toxic upon accumulation in the human body, it is urgent to develop accurate, low-cost, and on-site methods to detect multiple heavy metal ions in real water samples. Quantum dots (QDs) are an approved choice for use in sensors and exhibit favorable luminescence in aqueous solution, but they often become quenched when isolated from their suspensions due to agglomeration. Therefore, QDs must exist in a solid state in order to be successfully applied to luminescence detection. This work reports the fabrication of a novel luminescence composite based on glutathione-capped Mn-doped ZnS quantum dots (GSH-Mn-ZnS QDs) and layered double hydroxides (LDH). The composite is solid and exhibits enhanced luminescence intensity, as the structure of LDH prevents the aggregation of QDs. Most importantly, it exhibits a similar response when used as a sensor for detecting Pb2+, Cr3+ and Hg2+ with a linear range of 1 × 10−6 M to 1 × 10−3 M for each heavy metal, and a detection limit for the mixed metal ions of 9.3 × 10−7 M. In addition, the composite was successfully applied for detection in lake water with low interference. Therefore, a practical method is presented for the design and fabrication of a QD–LDH composite that can be used for qualitative and quantitative testing of mixed heavy metal ions simultaneously in real water samples.

•Cadmium-free QLEDs were fabricated via a simple solution-processed technique.•The Cu-In-Zn-S/ZnS nanocrystals exhibited bright solid-state emission.•The cadmium-free QLEDs had a very low turn-on voltage and an improved performance.High-efficiency green, yellow and red quantum-dot light emitting devices (QLEDs) have been fabricated via a simple solution-processed technique, in which different-colored Cu-In-Zn-S/ZnS core/shell colloidal semiconductor nanocrystals (NCs) are used as emissive layers sandwiched between an organic holes transport layer and an electron transport layer of ZnO nanoparticles. The yellow QLEDs exhibit a low turn-on voltage of 1.8 V and high luminance of 3061 cd/m2 as well as the peak external quantum efficiency (EQE) of 2.42%. In contrast, the green and red QLEDs show a low turn-on voltage of 2 V, and their electroluminescence (EL) peaks are located at 540 and 642 nm with the peak EQE of 0.25% and 0.91%, respectively. The solution-processed high-efficiency cadmium-free QLEDs with a low turn-on voltage and good reproducibility may become one of the most promising next generation of display.

•A simple surfactant-assisted colloidal approach was employed to prepare highly luminescent organometal halide perovskite QDs.•The CH3NH3PbBr3 QDs exhibited strong size-dependent optical properties due to quantum confinement effects.•The emission color of the halide perovskite QDs could be tuned by changing the halogen elements.Size-tunable organometal halide perovskite CH3NH3PbBr3 quantum dots (QDs) were successfully synthesized by a simple surfactant-assisted reprecipitation technique, in which the size-tunability was realized by varying the molar ratios of methylammonium bromide (CH3NH3Br) to PbBr2 while the total amount of octylamine (OTAm) and CH3NH3Br remained unchanged. The diameters of CH3NH3PbBr3 QDs could be effectively tuned from 1.6 to 3.9 nm, and these QDs exhibited an obviously size-dependent optical properties, whose photoluminescence (PL) covered the spectral region from 440 to 530 nm and the emission width was 20–32 nm. The maximum absolute PL quantum yield (PLQY) was measured to be as high as approximately 80% at room temperature. A plausible formation mechanism was proposed and the quantum confinement effect was discussed based on effective mass approximation. Moreover, this synthetic approach could also be extended to prepare different halide perovskite QDs including CH3NH3PbClxBr3−x and CH3NH3PbBr3−x Ix (x = 1–3), which realized the color-tunability over the entire visible spectral region of 390–750 nm. The size- and compositional-tunable emission colors of organometal perovskite QDs endows them wide potential applications in next-generation optoelectronic devices.

•Spin-coating a PEDOT:PSS layer on the ITO to improve the electric properties of EBDs for the first time.•The influence of annealing on the electric properties of EBDs is investigated.•The current transport mechanism of the different types of devices is discussed in detail.Hybrid organic/inorganic electrically bistable devices (EBDs) based on Cu2S/PVK nanocomposites have been fabricated by using a simple spin-coating method. An obvious electrical bistability is observed in the current-voltage (I-V) characteristics of the devices, and the presence of the buffer layer and the annealing process have an important effect on the enhancement of the ON/OFF current ratios. Different electrical conduction mechanisms are responsible for the charge switching of the devices in the presence and absence of the buffer layer.

Cu2−xS nanocrystals with different morphologies and crystal phases have been synthesized by using a simple one-pot and phosphine-free colloidal method, in which different alkanethiols (CnH2n+1SH, n = 8, 12, 18) have been selected as sulfur sources and capping ligands. The crystal phase can be transformed from monoclinic Cu1.94S to tetragonal Cu1.81S by varying the alkyl chain length of alkanethiols, and the morphology changes from nanospheres to nanodisks during the phase transformation. Strong localized surface plasmon resonance (LSPR) absorbance in the near-infrared (NIR) region has been observed in these Cu2−xS nanocrystals, which originates from excess holes in the valence band due to copper deficiencies. The alkyl chain length of alkanethiols plays an important role in the crystal phase, morphology and plasmonic properties of the as-obtained Cu2−xS nanocrystals.

Porous Y2O3:Er plates with enhanced upconversion luminescence properties have been synthesized through a hydrothermal method, followed by a post thermal treatment. The as-obtained products exhibit red (650–670 nm,4F9/2→4I15/2) and green emission bands (520–570 nm, 2H11/2, 4S3/2→4I15/2) under 980 nm pumping. The shape and size of the pores in the plates can be tuned by controlling the reaction time in the autoclave. Moreover, the porous structure induces surface defects, which greatly affect the upconversion luminescence intensity and decay time. The potential mechanism for the effects of surface defects on the upconversion intensity and decay time was investigated, which could be a new complement for upconversion luminescence.Highlights► The upconversion material with porous structure Y2O3:Er has been hydrothermally synthesized. ► The pore size and shape can be tuned by controlling the reaction time in the autoclave. ► The mechanism of surface defects effect the upconversion intensity and life time.was analyzed. ► They could be a new complement for UC luminescence.

A facile one-pot heating process without any injection has been developed to synthesize different Cu–Zn–S-based nanocrystals. The composition of the products evolves from Cu(I)-doped ZnS (ZnS:Cu(I)) nanocrystals into heterostructured nanocrystals consisting of monoclinic Cu1.94S and wurtzite ZnS just by controlling the molar ratios of zinc acetylacetonate (Zn(acac)2) to copper acetylacetonate (Cu(acac)2) in the mixture of n-dodecanethiol (DDT) and 1-octadecene (ODE). Accompanying the composition transformation, the crystal phase of ZnS is changed from cubic zinc blende to hexagonal wurtzite. Depending on the synthetic parameters including the reaction time, temperature, and the feeding ratios of Zn/Cu precursors, the morphology of the as-obtained heterostructured nanocrystals can be controlled in the forms of taper-like, matchstick-like, tadpole-like, or rod-like. Interestingly, when the molar ratio of Cu(acac)2 to Zn(acac)2 is increased to 9:1, the crystal phase of the products is transformed from monoclinic Cu1.94S to the mixed phase composed of cubic Cu1.8S and tetragonal Cu1.81S as the reaction time is further prolonged. The crystal-phase transformation results in the morphological change from quasi-spherical to rice shape due to the incorporation of Zn ions into the Cu1.94S matrix. This method provides a simple but highly reproducible approach for synthesis of Cu(I)-doped nanocrystals and heterostructured nanocrystals, which are potentially useful in the fabrication of optoelectronic devices.

Spherical silver sulfide (Ag2S) nanoparticles have been synthesized using a simple and one-pot route, which is a direct heating process using silver acetate and n-dodecanethiol as raw materials.Transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and selected area electron diffraction (SAED) were used to confirm the size, morphology and crystal structure of as-obtained Ag2S nanoparticles. The size of the products can be tuned by controlling the reaction time, and the growth process of the samples has been studied by employing UV–vis absorption spectra. Furthermore, these Ag2S nanoparticles have a high tendency to self-assemble into two- or three-dimensional superlattice structures. This one-pot approach may be extended to synthesis of other metal sulfides nanoparticles.Highlights► Spherical Ag2S nanoparticles were synthesized by a one-pot route. ► The growth process was studied by using UV–vis absorption spectra and XRD patterns. ► The Ag2S nanoparticles have a high tendency to self-assemble into superlattice structures.

A one-step colloidal process was adopted to prepare face-centered-cubic PbS nanocrystals with different shapes such as octahedral, starlike, cubic, truncated octahedral, and truncated cubic. The features of this approach avoid the presynthesis of any organometallic precursor and the injection of a toxic phosphine agent. A layered intermediate compound (lead thiolate) forms in the initial stage of the reaction, which effectively acts as the precursor to decompose into the PbS nanocrystals. The size and shape of the PbS nanocrystals can be easily controlled by varying the reaction time, the reactant concentrations, the reaction temperatures, and the amount of surfactants. In particular, additional surfactants other than dodecanethiol, such as oleylamine, oleic acid, and octadecene, play an important role in the shape control of the products. The possible formation mechanism for the PbS nanocrystals with various shapes is presented on the basis of the different growth directions of the nanocrystals with the assistance of the different surfactants. This method provides a facile, low-cost, highly reproducible process for the synthesis of PbS nanocrystals that may have potential applications in the fabrication of photovoltaic devices and photodetectors.

High-quality spherical silver (Ag) nanocrystals have been synthesized by using a one-pot approach, in which pre-synthesis of organometallic precursors is not required. This reaction involves the thermolysis of a mixed solution of silver acetate and n-dodecanethiol in a non-coordinating organic solvent. The size of the as-obtained Ag nanospheres can be controlled by adjusting the reaction time, reaction temperature and the amount of silver acetate added. The growth and nucleation process of the resultant Ag nanospheres have been studied by employing UV–vis absorption spectra and transmission electron microscopy (TEM) images. Furthermore, these Ag nanospheres have good self-assembly behaviors, and they are easily self-assembled into two- or three-dimensional superlattice structures due to the bundling and interdigitation of thiolate molecules adsorbed on Ag nanospheres. This one-pot synthetic procedure is simple and highly reproducible, which may be extended to prepare other noble-metal nanocrystals.Graphical abstractDifferent sized and monodisperse silver nanospheres were prepared using a one-pot approach with no pre-synthesis of organometallic precursors, and the silver nanospheres can self-assemble into highly ordered superlattices.Highlights► Monodisperse silver nanospheres have been synthesized by a one-pot approach. ► The synthetic method does not need pre-synthesis of organometallic precursors. ► The silver nanospheres can self-assemble into highly ordered superlattices. ► This synthetic method can be extended to prepare other metal nanocrystals.

A simple solvothermal approach employing oleic acid has been developed to prepare anatase TiO2 nanocrystals with different shapes, which were tuned from nanorods to nano-ellipsoids by increasing the amount of NaF from 0 to 0.5 mmol, and the optical band gap decreased from 3.47 eV to 3.29 eV accordingly. However, when the fluoride was changed to NH4F, the resultant TiO2 nanocrystals possessed an anatase phase but were made up of smaller-sized nanocrystals and nanorods, and the band gap was increased to 3.53 eV. The X-ray photoelectron spectroscopy (XPS) results illustrated an increase of fluorine content with an increasing amount of NaF could account for the variation of the shape and optical band gap of TiO2 nanocrystals. Moreover, the absence of fluorine content brought about less change of shape and increase of optical band gap of the product synthesized in the presence of NH4F. This result may offer another way to alter the shape and band gap of metal oxide nanocrystals with the assistance of fluoride.A simple solvothermal approach is described to prepare anatase TiO2 nanocrystals exhibiting different shapes from nanorods to nano-ellipsoids with the assistance of fluoride.

•CsPbBr3 perovskite nanocrystals have been synthesized in the presence of organic amines with different hydrocarbon length.•The photoluminescence of the CsPbBr3 nanocrystals is affected by the varying the carbon length of the organic amines.•The lower reaction temperature and hydrocarbon chain length of the organic ligands play a significant role in the self-assembly of CsPbBr3 nanocrystals.All-inorganic halide perovskites have become one of the most prospective materials for lightening and display technology due to their color-tunable and narrow-band emission. Herein, we have systematically studied the effects of organic amines with different hydrocarbon chain length on the optical properties and morphology as well as the crystal structure of colloidal CsPbBr3 nanocrystals (NCs), which were synthesized in the presence of oleic acid (OA) and organic amines by using a simple hot-injection approach. The hydrocarbon chain length has shown an independent correlation to the morphology and crystal structure of the as-obtained CsPbBr3 NCs at 160 °C, but their optical properties can be affected to some extent. The photoluminescence quantum yields (PLQYs) of the CsPbBr3 NCs synthesized in the presence of organic amines with long carbon chain length are generally in the range of 55–80% for different reaction time, but the PLQYs of less than 20% are obtained for the products synthesized in the presence of octylamine (OTAm) with short carbon chain length. The effects of the reaction temperature on the optical properties, size and crystal structure of the CsPbBr3 NCs synthesized in the presence of cetylamine (CTAm) are studied. Interestingly, some nanoplates also appear in these CsPbBr3 NCs obtained at relatively low temperatures (120 and 140 °C), which have a strong tendency to self-assemble into face-to-face nanostructures. Such a similar self-assembly behavior is also observed in the product synthesized in the presence of oleylamine (OLAm), but only flat nanoplates are observed in the products in the presence of OTAm at 120 °C. The results indicate that the lower reaction temperature and hydrocarbon chain length of the organic ligands play a significant role in the self-assembly of CsPbBr3 NCs. This work opens up an alternative approach to controllable-synthesis of perovskite NCs through varying the carbon chain length of organic surfactants, and enlightens the fabrication of different nanostructures via self-assembly methods for further optoelectronic applications.

As most heavy metals are highly toxic upon accumulation in the human body, it is urgent to develop accurate, low-cost, and on-site methods to detect multiple heavy metal ions in real water samples. Quantum dots (QDs) are an approved choice for use in sensors and exhibit favorable luminescence in aqueous solution, but they often become quenched when isolated from their suspensions due to agglomeration. Therefore, QDs must exist in a solid state in order to be successfully applied to luminescence detection. This work reports the fabrication of a novel luminescence composite based on glutathione-capped Mn-doped ZnS quantum dots (GSH-Mn-ZnS QDs) and layered double hydroxides (LDH). The composite is solid and exhibits enhanced luminescence intensity, as the structure of LDH prevents the aggregation of QDs. Most importantly, it exhibits a similar response when used as a sensor for detecting Pb2+, Cr3+ and Hg2+ with a linear range of 1 × 10−6 M to 1 × 10−3 M for each heavy metal, and a detection limit for the mixed metal ions of 9.3 × 10−7 M. In addition, the composite was successfully applied for detection in lake water with low interference. Therefore, a practical method is presented for the design and fabrication of a QD–LDH composite that can be used for qualitative and quantitative testing of mixed heavy metal ions simultaneously in real water samples.