ZnSe Nanocrystals Research Articles

Structural, optical and Raman studies of template-free solvothermally synthesized ZnSe/ZnSe:Ce 3+ nanoparticles

The present work reports a general, single step and easy solvothermal method to synthesize well crystallized and pure phase Ce 3+ doped ZnSe nanocrystals for the first time in a unified system. The products were well characterized by powder X-ray diffraction (XRD), UV–vis spectroscopy (UV–vis), photoluminescence spectroscopy (PL), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray diffraction (EDAX) and Raman spectroscopy. The products were found to show significant finite size effect as characterized by broadened XRD peaks, blue-shifts of the interband optical absorption edge and the asymmetric broadening of Raman spectra. The emission intensity of Ce 3+ ion doped ZnSe was found to be considerably increased with respect to the pure one. The observed lineshape of LO modes indicates broadening that is due to the nanosized effect. The structure and properties were correlated and detailed growth mechanism is also discussed.

Synthesis of Highly Emissive Mn-Doped ZnSe Nanocrystals without Pyrophoric Reagents

Manganese-doped zinc selenide quantum dots (Mn:ZnSe d-dots) with high optical quality, pure dopant emission with 40−60% photoluminescence quantum yield, were synthesized with air-stable and generic starting materials, namely zinc (manganese) fatty acid salts with corresponding free fatty acids, Se powder, fatty amine, and octadecene. The pyrophoric, highly toxic, and expensive organo-phospines were eliminated from the existing synthetic protocols for high quality Mn:ZnSe d-dots, which changed the reaction profile substantially mainly because of the enhanced reactivity of elemental Se with the presence of fatty amines. The reaction temperatures for two key processes involved in “nucleation-doping”, namely, formation of MnSe nanoclusters and their overcoating by the host, were both reduced. Multiple injection techniques were employed to realize balanced diffusion of the Mn ions in the d-dots. The resulting d-dots were found to be in zinc-blende crystal structure, with optimal spherical shape, nearly monodispersed, and controlled in their Mn:Zn ratio.

Size- and shape-controlled synthesis of ZnSe nanocrystals using SeO2 as selenium precursor

Here we report a low-cost and "green" phosphine-free route for the size- and shape-controlled synthesis of high-quality zinc blende (cubic) ZnSe nanocrystals. To avoid the use of expensive and toxic solvents such as trioctylphosphine (TOP) or tributylphosphine (TBP), SeO(2) was dispersed in 1-octadecene (ODE) as a chalcogen precursor. It has been found that the temperature and the surface ligand influenced the nucleation, the reaction speed and the formation of different shapes. Absorption spectroscopy, fluorescence spectroscopy, powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used for the characterization of the as-synthesized ZnSe nanocrystals. The size-dependent photoluminescence (PL) range of the as-prepared ZnSe nanocrystals was between 390 and 450 nm, with the PL full width at half-maximum (FWHM) well controlled between 14 and 18 nm and PL quantum yields reached up to 40% at room temperature. Moreover, this new selenium precursor can be used to form tetrapod-shaped ZnSe nanocrystals when zinc acetylacetonate was introduced as the zinc precursor with a one-pot method.

“One-pot” synthesis and shape control of ZnSe semiconductor nanocrystals in liquid paraffin

In this paper, we demonstrated a “one-pot” strategy for synthesizing ZnSe nanocrystals (NCs) in liquid paraffin. All materials, including Zn source, Se source, and ligand, were mixed in liquid paraffin beforehand, which avoided the injection of Se source at high temperature. The resultant ZnSe NCs possessed high photoluminescence quantum yields and narrow size distribution. Moreover, the size, shape, and crystal phase of NCs were controllable by altering the experimental variables, such as precursor concentration, Zn:Se molar ratio, and heating rate. Because the raw materials used here were low-cost and environmentally friendly, this “one-pot” synthetic protocol would facilitate the commercial scale synthesis of high-quality ZnSe NCs.

Optical properties of conjugated polymer-ZnSe nanocrystal nanocomposites

Nanocomposites of poly[(2-methoxy,5-octoxy)1,4-phenylenevinylene]-zinc selenide (MOPPV-ZnSe) are synthesized by mixing the polymerization of 1,4-bis (chloromethyl)-2-methoxy-5-octoxy-benzene in the presence of ZnSe quantum dots. The resulting MOPPV-ZnSe nanocomposites possess a well-defined interfacial contact, thus significantly promoting the dispersion of ZnSe within the MOPPV matrix and facilitating the electronic interaction between these two components. Raman and UV–visible absorption spectra are influenced by the incorporation of ZnSe nanocrystals. High-resolution transmission electron microscopic and tapping-mode atomic force microscopic results show clearly the evidence for phase-segregated networks of ZnSe nanocrystals, which provide a large area of interface for charge separation to occur. Steady-state spectra of MOPPV-ZnSe nanocomposites are markedly quenched by the introduction of intimate polymer/ZnSe junctions. Time-resolved photoluminescence measurements show that the lifetime decays quickly, which further confirms the occurrence of charge transfer in MOPPV-ZnSe nanocomposites.

Prevention of photooxidation in blue–green emitting Cu doped ZnSe nanocrystals

This communication highlights unstable blue-green emitting Cu doped ZnSe nanocrystals stabilized by diluting the surface Se with a calculated amount of S.

An Alternate Route to High-Quality ZnSe and Mn-Doped ZnSe Nanocrystals

We report here a synthetic route for high-quality Mn-doped ZnSe nanocrystals using selenourea as a selenium source, avoiding the more conventional route using tributylphosphine (TBP) that restricts the growth of spherical ZnSe nanocrystals below 5 nm in size, besides being highly toxic and pyrophoric. Spherical ZnSe nanocrystals with unprecedented sizes (up to 12 nm) are synthesized, the large size of the host helps to keep dopant ions well inside the nanocrystal, leading to intense and stable dopant emission. Mn-doped ZnSe nanocrystals with more than 50% quantum yield (QY) are synthesized in this method and found to be stable both in aqueous and nonaqueous dispersions for months.

Strong green emission from ZnSe–Ag2Se nanocomposites

Nanocomposite materials usually exhibit unique properties compared to their single phase counterparts. In this work, ZnSe–Ag2Se nanocomposites were prepared via a high-temperature reflux route. The nanocomposites demonstrated strong green light emission, which was a significant red shift compared to that of ZnSe nanoparticles. The red-shifted photoluminescence (PL) was attributed to the defects arising from Ag doping in the domain of ZnSe nanocrystals of the nanocomposites, based on the results of PL and PL excitation measurements.

Theoretical investigation for ZnSe clusters: Influence of solvent and ligand on their characteristics

On the basis of experimental zinc blende and wurtzite of ZnSe nanocrystals, four structures Zn 3Se 3, Zn 4Se 4, (Zn 3Se 3) 2, (Zn 3Se 3) 3 and Se–Zn–SR clusters were studied at DFT/B3LYP/LANL2DZ theoretical level. First, Zn 3Se 3, (Zn 3Se 3) 2 and (Zn 3Se 3) 3 structures have the same units (hexagon) with wurtzite. Zn 4Se 4 has resemblant conformation with zinc blende for they are all composed of tetrahedron. Second, calculated Raman peaks of Zn 3Se 3, Zn 4Se 4, (Zn 3Se 3) 2 and (Zn 3Se 3) 3 are about 180 cm −1 that is consistent with the experimental result. Third, through investigation of Se–Zn–SR clusters, we have found that their stability, bond lengths and the wavelengths of the absorption peaks do not have essential difference in theory. It illuminates that the main influence of ligand comes from thiol. Finally, we detect that both solvent and ligand make the wavelengths of the absorption peaks shift to blue. With solvent and ligand, our wavelengths of the absorption peaks will be almost identical with experimental ZnSe nanocrystals. Moreover, the wavelengths of the absorption peaks shift to red in order Zn 3Se 3, (Zn 3Se 3) 2 and (Zn 3Se 3) 3, which is induced by quantum size effect. Besides, we also prove that the calculated absorption peaks of four structures are the transitions from HOMO to LUMO or from d to p orbital.

Preparation of Two-dimensional Array of Nanodots by Ferritin Template

Zinc selenide (ZnSe) nanocrystals were synthesized in the cavity of the apoferritin from horse spleen (HsAFr), and two-dimensional ZnSe-ferritin nanodots were prepared by simple touch method on modified silicon surface. In the synthesis, ZnSe nanocrystals are encapsulated and growth is restricted to the internal dimension of the protein cavity. The obtained nanodots were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and absorption measurements. In addition, the photoluminescence (PL) properties of two-dimensional nanodots were obtained. From the results, it was concluded that ZnSe nanocrystals were successfully synthesized in the core of ferritin and the monolayer of ZnSe-ferritin could be obtained on the surface of silicon wafer. In addition, the arrays on the silicon surface provided the PL emission peak for ZnSe quantum dots(QDs) in ferritin core. Accordingly, the ZnSe-ferritin arrays can be employed as a useful sensor material for PL technique such as fluorescence resonance energy transfer (FRET).

Effect of deposition parameters on structural, optical and electrical properties of nanocrystalline ZnSe thin films

This paper presents the chemical bath deposition of zinc selenide (n-ZnSe) nanocrystalline thin films on non-conducting glass substrates, in an aqueous alkaline medium using sodium selenosulphate as Se 2− ion source. The X-ray diffraction studies show that the deposited ZnSe material is nanocrystalline with a mixture of hexagonal and cubic phase. The direct optical band gap ‘ E g’ for the as-deposited n-ZnSe films is found to be 3.5 eV. TEM studies show that the ZnSe nanocrystals (NCs) are spherical in shape. Formation of ZnSe has been confirmed with the help of infrared (IR) spectroscopy by observing bands corresponding to the multiphonon absorption. We demonstrate the effect of the deposition temperature and reactant concentration on the structural, optical and electrical properties of ZnSe films.

A facile synthesis of zinc blende ZnSe nanocrystals

Since ZnSe is less toxic than cadmium based materials, ZnSe nanocrystal is a potential candidate for optoelectronic and fluorescent labelling applications. In this paper, colloidal ZnSe nanocrystals are successfully synthesized from zinc stearate and elemental selenium in a paraffin hot-matrix. The method is environment-friendly and of low cost compared with the conventional methods, which are generally toxic and expensive. The nanocrystal–nanocrystal interactions will significantly affect the optical properties and thus a detailed study is desirable. Here, we comprehensively study the interaction through the van der Waals interaction energy, electrostatic energy, steric energy and depletion interaction energy. The corresponding photoluminescence and absorption spectra show obvious excitonic features. Our results show that the nanocrystals can be converted to a water-dispersible system when the dominant emission is still from the excitonic recombination on ZnSe nanocrystals.

Photoluminescence of ZnSe nanocrystals at high excitation level

The excitation-dependent photoluminescence (PL) of ZnSe nanocrystals (NCs) grown on GaAs (100) substrate is studied. The PL spectra observed corroborate previous observations of a bimodal size distribution of the NCs grown, and, in addition, evidence the existence of spectral diffusion with an extent dependent on excitation power. Besides, it is also shown that at relatively intense excitation an extra band arises in the luminescence spectra due to biexcitons confined in NCs of 3.5–4.0nm size. The binding energy of these biexcitons is as large as 23meV.

Role of Redox Reaction and Electrostatics in Transition-Metal Impurity-Promoted Photoluminescence Evolution of Water-Soluble ZnSe Nanocrystals

In this article, the experimental variable-dependent photoluminescence (PL) evolution of transition-metal-doped ZnSe nanocrystals (NCs) is analyzed by combining the redox reaction and the electrostatics of aqueous NCs. Bulk doping of NCs involves two steps − surface adsorption of the metal impurities and the followed internal doping. The former relates to the electrostatics of aqueous NCs, whereas the latter relates to a redox reaction between the impurities and mercapto-ligands. Both of them occur on the NC surface. In this context, aqueous NCs are essentially charge-stabilized particles. The electrostatic factors that weaken the electrostatic repulsion will facilitate the adsorption of metal impurities on NC surfaces, thus benefiting the surface redox reaction. It furthermore promotes the internal doping of the metal impurities. Consequently, the trap emission and the PL evolution of NCs are facilitated. Besides, the internal doping is favored for the metal impurities with high reduction potential because they are easily reduced by mercapto-ligands. Furthermore, because the presence of metal impurities in NC solution both promotes the oxidation of mercapto-ligands and weakens the interparticle electrostatic repulsion, the colloidal solution of doped aqueous NCs is theoretically proved unstable.

Role of Confinement on Diffusion Barriers in Semiconductor Nanocrystals

We find that quantum size effects not only play an important role in the electronic properties of defects in semiconductor nanocrystals, but also strongly affect the incorporation of defect atoms into the nanocrystals. In particular, using ab initio methods based on density functional theory, we predict that Mn defects will be energetically driven towards the surface of CdSe and ZnSe nanocrystals, and that the diffusion barrier of a Mn interstitial defect in a CdSe nanocrystal will be significantly lower than that in the bulk.

Phosphine-free synthesis of high quality ZnSe, ZnSe/ZnS, and Cu-, Mn-doped ZnSe nanocrystals

High quality zinc blende ZnSe and ZnSe/ZnS core/shell nanocrystals have been synthesized by two converse injection methods (i.e. zinc precursor injection or selenium precursor injection) when Se-ODE complex was chosen as the phosphine-free selenium precursor. Absorption spectroscopy, fluorescence spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM) were used to characterize the as-synthesized ZnSe and ZnSe/ZnS nanocrystals. The quality of the as-prepared ZnSe nanocrystals reached the same high level compared with the method using phosphine selenium precursors since the quantum yields were between 40 and 60% and photoluminescence (PL) full width at half-maximum (FWHM) was well controlled between 14 and 17 nm. The parameter window for the growth of high quality ZnSe nanocrystals was found to be much broader and monodisperse ZnSe nanocrystals were synthesized successfully even when the reaction temperature was set as low as 240 degrees C. As cores, such zinc blende ZnSe nanocrystals were also used to synthesize ZnSe/ZnS core/shell nanocrystals with high fluorescence quantum yields of 70%. Cu(2+) or Mn(2+) doped ZnSe nanocrystals were also synthesized by simply modifying this phosphine-free method. The emission range has been extended to 500 and 600 nm with the use of Cu(2+) and Mn(2+) dopants compared with the emission coverage of ZnSe at around 400 nm. This is the first totally "green approach" (i.e. phosphine-free synthesis) for the synthesis of high quality ZnSe, ZnSe/ZnS, and Cu(2+) or Mn(2+) doped ZnSe nanocrystals.

A simple way of shape-controlled synthesis of ZnSe nanocrystals : nanodots, nanoflowers, and nanotubes

By introducing aliphatic amines in high concentration, the shapes of ZnSe nanocrystals could be controlled through different stirring duration of zinc precursors.

Synthesis of Colloidal ZnSe Nanospheres by Ultrasonic-Assisted Aerosol Spray Pyrolysis

Colloidal monodisperse ZnSe nanospheres consisting of primary nanocrystals were prepared by aerosol spray pyrolysis with ultrasonic nebulization. The formation mechanism of nanospheres seems to be generation of primary ZnSe nanocrystals and subsequent aggregation of primary nanocrystals in a tube reactor. Monodispersed ZnSe nanospheres were found to be synthesized only from a specific mixture of precursors at a reaction temperature of 525 °C. Typical ratios were ZnO (5 mmol)/OA (10 mL)/TOPO (2 g)/ODE (10 mL) as a Zn precursor and Se (10 mmol)/TOP (5 mL)/ODE (5 mL) as a Se precursor. Those ZnSe nanoparticles were characterized by TEM, EDX, FT-IR, UV−vis, and PL techniques. The TEM image shows that the average diameter of ZnSe nanospheres is 41 nm, and primary ZnSe nanocrystals have a size of 2−3 nm. The XRD pattern of ZnSe nanoparticles shows that the crystal structure is zinc blende. The ZnSe nanospheres were confirmed to have a quantum size effect in their optical spectra and exhibit near band-edge lumin...

Inorganic–organic hybrid semiconductor nanomaterials: (ZnSe)(N 2H 4) x(C 5H 5N) y

In this paper, inorganic–organic hybrid semiconductor (ZnSe)(N 2H 4) x (C 5H 5N) y nanosheets as well as (ZnSe)(C 5H 5N) y nanoparticles were first synthesized by a solvothermal method in a ternary solution and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectra, ultraviolet–visible (UV–vis) absorption spectra, thermogravimetric analysis (TGA), differential scanning calorimeter (DSC) and photoluminescence (PL) spectra. The results indicated that the morphology and composition of the products were largely influenced by the reaction temperature and the volume ratio of water. When the reaction temperature and the water content were lower, (ZnSe)(N 2H 4) x (C 5H 5N) y nanosheets were formed. As the reaction temperature or the content of water was high enough, (ZnSe)(C 5H 5N) y nanoparticles were formed. Pure hexagonal wurtzite ZnSe nanosheets or zinc blende ZnSe nanoparticles were obtained by extracting the corresponding hybrids. The bandgap absorption of ZnSe nanocrystals blue shifted in comparison with the bulk. The photoluminescent intensity of (ZnSe)(N 2H 4) x (C 5H 5N) y nanosheets was much stronger than that of (ZnSe)(C 5H 5N) y nanoparticles.

Synthesis and characterization of blue emitting ZnSe quantum dots

In this work we show a new experimental methodology to obtain ZnSe nanocrystals in aqueous solution aiming their application as biophotonic probes. The nanocrystals were obtained using a simple procedure based on the arrested precipitation of ZnSe in aqueous solution in the presence of a thiol-alkyl stabilizing agent, in air and at room temperature. Using post-preparative experimental procedures on the colloidal particles, blue and green emissions were observed. The structural characterization (powder X-ray diffraction and electronic transmission microscopy) shows that the particles were obtained in the quantum confinement regime (d=2–4nm) and possess a zinc-blend crystalline structure. The optical properties of the suspensions were determined by electronic absorption, excitation and emission spectroscopies and are discussed in terms of their size and chemical compositions.