Structural and optical properties of Mn doped ZnS semiconductor nanostructures

Manganese doped zinc sulphide nanoparticles were fabricated by adopting an inexpensive solution growth route. Different samples were fabricated by varying Mn concentrations. UV-VIS study reveals blue-shift on the onset of absorption and hence enhancement in the optical band gap upto 0.75 eV, indicating strong quantum confinement. Photoluminescene study for all the samples display characteristic band edge peak at ∼410 nm. The broad peak ∼560–580 nm is ascribed to Mn incorporation. Further, structural investigations were carried out by using X-Ray diffraction and transmission electron microscopy (TEM).     

Calculation of the quantum efficiency for the absorption on confinement levels in quantum dots

The quantum efficiency of the absorption on quantum confinement levels is investigated. This is achieved by modeling the electron confinement in a spherical quantum dot (QD). The confinement levels are calculated using both infinite and finite rectangular quantum wells. The spectral internal quantum efficiency is evaluated within both the models, by computing Einstein’s coefficients for the transitions between confinement levels. The size of QDs (1–3 nm radius) leads to negligible many body effects. The nature of the QD material and of the matrix embedding is taken into account in the finite rectangular quantum well approximation and introduces only a small correction. The temperature dependence of the efficiency is also taken into account. A numerical application is performed for a silicon QD of 2.5 nm radius, embedded in amorphous silica. It is proved that the absorption threshold shifts toward the far infrared limit and that the spectral internal quantum efficiency reaches 4–5% at the threshold.     

Hybrid polymer-CdS solar cell active layers formed by in situ growth of CdS nanoparticles

The integration of semiconductor nanoparticles (NPs) into a polymeric matrix has the potential to enhance the performance of polymer-based solar cells taking advantage of the physical properties of NPs and polymers. We synthesize a new class of CdS-NPs-based active layer employing a low-cost and low temperature route compatible with large-scale device manufacturing. Our approach is based on the controlled in situ thermal decomposition of a cadmium thiolate precursor in poly(3-hexylthiophene) (P3HT). The casted P3HT:precursor solid foils were heated up from 200 to 300 °C to allow the precursor decomposition and the CdS-NP formation within the polymer matrix. The CdS-NP growth was controlled by varying the annealing temperature. The polymer:precursor weight ratio was also varied to investigate the effects of increasing the NP volume fraction on the solar cell performances. The optical properties were studied by using UV–Vis absorption and photoluminescence (PL) spectroscopy at room temperature. To investigate the photocurrent response of P3HT:CdS nanocomposites, ITO/P3HT:CdS/Al solar cell devices were realized. We measured the external quantum efficiency (EQE) as a function of the wavelength. The photovoltaic response of the devices containing CdS-NPs showed a variation compared with the devices with P3HT only. By changing the annealing temperature the EQE is enhanced in the 400–600 nm spectral region. By increasing the NPs volume fraction remarkable changes in the EQE spectra were observed. The data are discussed also in relation to morphological features of the interfaces studied by Focused Ion Beam technique.     

Size control synthesis of starch capped-gold nanoparticles

Metallic gold nanoparticles have been synthesized by the reduction of chloroaurate anions [AuCl₄]⁻ solution with hydrazine in the aqueous starch and ethylene glycol solution at room temperature and at atmospheric pressure. The characterization of synthesized gold nanoparticles by UV–vis spectroscopy, high resolution transmission electron microscopy (HRTEM), electron diffraction analysis, X-ray diffraction (XRD), and X-rays photoelectron spectroscopy (XPS) indicate that average size of pure gold nanoparticles is 3.5 nm, they are spherical in shape and are pure metallic gold. The concentration effects of [AuCl₄]⁻ anions, starch, ethylene glycol, and hydrazine, on particle size, were investigated, and the stabilization mechanism of Au nanoparticles by starch polymer molecules was also studied by FT-IR and thermogravimetric analysis (TGA). FT-IR and TGA analysis shows that hydroxyl groups of starch are responsible of capping and stabilizing gold nanoparticles. The UV–vis spectrum of these samples shows that there is blue shift in surface plasmon resonance peak with decrease in particle size due to the quantum confinement effect, a supporting evidence of formation of gold nanoparticles and this shift remains stable even after 3 months.     

Polypyrrole–silica core–shell nanocomposites: a new route towards active materials in dielectrophoretic displays

A direct route to polypyrrole–silica core–shell nanoparticles with diameters in the 150–300 nm range is described to design new nanocomposites, in which the conducting part is wrapped by an external silica shell in order to obtain finally neutral conductive nanoparticles. The nanocomposites are characterized by SEM, FTIR, electrochemistry and thermal gravimetric analysis, demonstrating that the external silica shell actually insulates the conjugated polymer from the outer medium. In a second step, the nanocomposites are coated with an additional PDMS layer. The electrorheological properties of the ink made by dispersion of these final nanoparticles in a low dielectric constant fluid are checked in a dielectrophoretic device, in which the motion of the particles induced by an external electric field can be used to monitor a switch of the light transmission properties with a low voltage threshold.     

Fabrication of ceramic oxide-coated SWNT composites by sol–gel process with a polymer glue

The functional copolymer bearing alkoxysilyl and pyrene groups, poly[3-(triethoxysilyl)propyl methacrylate]-co-[(1-pyrene-methyl) methacrylate] (TEPM₁₃-co-PyMMA₃), was synthesized via atom transfer radical polymerization. Attributing the π–π interaction of pyrene units with the walls of single-walled carbon nanotubes (SWNTs), this polymer could disperse and exfoliate SWNTs in different solvents through physical interaction as demonstrated by TEM, UV/Vis absorption, and FT-IR analysis. The alkoxysilyl groups functionalized SWNTs were reacted with different inorganic precursors via sol–gel reaction, and, as a results, silica, titania, and alumina were coated onto the surface of SWNTs, respectively via copolymers as a molecular glue. The nanocomposites of ceramic oxides/SWNTs were characterized by SEM analysis. Dependent upon the feed, the thickness of inorganic coating can be tuned easily. This study supplies a facile and general way to coat SWNTs with ceramic oxides without deteriorating the properties of pristine SWNTs.     

Use of short-wavelength synchrotron radiation to measure luminescence quantum yield and the luminescence excitation spectrum of polymers

We describe an optical diagnostics module and the instrumental and methodological features of ultrahigh vacuum experiments investigating the optical characteristics of condensed media in the short-wavelength (hv ~ 3.5–25 eV) range of the spectrum of probing synchrotron radiation. We give a brief presentation of the results of an experimental determination of the spectral dependence of the luminescence quantum yield and the luminescence excitation spectrum of ablatable polymer dielectrics on the Kurchatov synchrotron radiation source at values of the probing radiation power density (I ₀ ~ 10¹² photons/cm²∙sec) that are below threshold for extended surface vaporization and a surface temperature of the condensed targets equal to 77–300 K.     

Synthesis of hydrophobic gold nanoclusters: growth mechanism study,luminescence property and catalytic application

One-pot synthesis of well dispersed, size-controlled gold nanoparticles with the average size of 10–15 nm and luminescent gold nanoclusters with average size of 1.7–2.0 nm were successfully achieved by thermal decomposition of gold organometallic precursor CH₃AuPPh₃ in the presence of thiol surfactants in o-xylene. Only difference between the preparations of two types of Au nanoparticles is the amount of thiol surfactant employed. The mechanistic study of formation of gold nanoparticles was carried out by analyzing the samples at different reaction time intervals and revealed that two-staged growth process was involved. The nanoclusters showed strong red emission with the maximum intensity at about 600 nm. The maximum room temperature photoluminescence quantum yield was measured as 1.2%. The catalytic ability of the Au nanoclusters to promote Suzuki–Miyaura coupling involving the C–C bond formation was also investigated.     

Fluorescence studies of confinement in polymer films and nanocomposites: Glass transition temperature, plasticizer effects, and sensitivity to stress relaxation and local polarity

Confinement effects in polystyrene and poly(methyl methacrylate) films and nanocomposites are studied by fluorescence. The ability to employ an intensive measurable, the excited-state fluorescence lifetime, in defining the glass transition temperature, T_g, of polymers is demonstrated and compared to the use of an extensive measurable, fluorescence intensity. In addition, intrinsic fluorescence from the phenyl groups in polystyrene is used to determine the T_g-confinement effect in films as thin as ~15 nm. The decrease in T_g with decreasing film thickness (below ∼60 nm) agrees well with results obtained by extrinsic pyrene fluorescence. Dye label fluorescence is used to quantify the enhancement in T_g observed with decreasing thickness (below ~90 nm) in poly(methyl methacrylate) films; addition of 2–4 wt% dioctyl phthalate plasticizer reduces or eliminates the T_g-confinement effect in films down to 20 nm thickness. Intrinsic polystyrene fluorescence, which is sensitive to local conformation, is used to quantify the time scales (some tens of minutes) associated with stress relaxation in thin and ultrathin spin-coated films at T_g + 10 K. Finally, the shape of the fluorescence spectrum of pyrene doped at trace levels in polystyrene films and polystyrene-silica nanocomposites is used to determine effects of confinement on microenvironment polarity.     

Maghemite/poly(<Emphasis Type="SmallCaps">d,l</Emphasis>-lactide-<Emphasis Type="Italic">co</Emphasis>-glycolyde) composite nanoplatform for therapeutic applications

A reproducible methodology is described for the synthesis, by following the double emulsion/solvent evaporation technique, of magnetic nanocomposites (average diameter ≈ 135 nm) consisting of maghemite nuclei and a biodegradable poly(d,l-lactide-co-glycolide) matrix. The heterogeneous structure of the nanoparticles can confer them the responsiveness to magnetic gradients, giving both the possibility of their use as a drug delivery system and adequate heating characteristics for a hyperthermia effect. The physical chemistry of the nanocomposites was extensively characterized, this establishing that their surface properties were similar to that of pure poly(d,l-lactide-co-glycolide). From an electrokinetic point of view, zeta potential determinations (as a function of the ionic strength, and pH) pointed out that the nanocomposites were almost indistinguishable from the copolymer. The surface thermodynamic analysis agreed with the electrophoretic one in suggesting that the coverage of the magnetic nuclei was complete, since the hydrophilic nature of maghemite was modified and the nanoparticles turned into hydrophobic, just like the copolymer, when they were embedded into poly(d,l-lactide-co-glycolide). The magnetic behaviours of the composite nanoparticles were also checked. Their heating properties were studied in vitro in a high-frequency alternating gradient of magnetic field: a stable maximum temperature of 47 °C was satisfactorily achieved within 45 min. Blood compatibility of the nanocomposites was also defined in vitro. To our knowledge, this is the first time that such kind of magnetic-sensitive nanoformulation with very promising characteristics (e.g. blood compatibility, magnetic drug targeting capabilities, and hyperthermia) has been developed for therapeutic purposes.     

Luminescence Properties of Metal(II)-Diethyldithiocarbamate Chelate Complex Particles and Its Analytical Application

In a suitable pH buffer solutions, sodium diethyldithiocarbamate (DDTC) reacts with some divalence metal ions M(II) to form (M–DDTC) _n chelate complex nanoparticles, which exhibit different luminescence properties. There is a strongest luminescence peak at 470 nm for the Co(II)–DDTC system, three peaks at 330, 470, and 630 nm for the Cu(II)–DDTC system, three peaks at 420, 470, and 630 nm for the Cd(II)–DDTC system, four peaks at 350, 400, 435, and 470 nm for the Ni(II)–DDTC system, two peaks at 408 and 470 nm for the Pb(II)–DDTC system, two peaks at 415 and 470 nm for the Fe(II)–DDTC system. The different luminescence properties of (M–DDTC) _n chelate complex nanoparticles was explained. Under the optimal conditions, the luminescence intensity of (Co–DDTC) _n chelate complex nanoparticles at 470 nm (F _{470 nm}) is linear to Co(II) concentration in the range of 0.012–1.44 μg/mL. The detection limit is 0.0023 μg/mL. A novel luminescence method has been proposed for the determination of cobalt in Vitamin B₁₂ samples, with satisfactory results.     

A simple route to prepare stable hydroxyapatite nanoparticles suspension

A simple ultrasound assisted precipitation method with addition of glycosaminoglycans (GAGs) is proposed to prepare stable hydroxyapatite (HAP) nanoparticles suspension from the mixture of Ca(H₂PO₄)₂ solution and Ca(OH)₂ solution. The product was characterized by XRD, FT-IR, TEM, HRTEM and particle size, and zeta potential analyzer. TEM observation shows that the suspension is composed of 10–20 nm × 20–50 nm short rod-like and 10–30 nm similar spherical HAP nanoparticles. The number-averaged particle size of stable suspension is about 30 nm between 11.6 and 110.5 nm and the zeta potential is −60.9 mV. The increase of stability of HAP nanoparticles suspension mainly depends on the electrostatic effect and steric effect of GAGs. The HAP nanoparticles can be easily transported into the cancer cells and exhibit good potential as gene or drug carrier system.     

Optoelectronic properties of Ni–GaP diodes with a modified surface

We report the promising results for Ni–GaP Schottky diode structures manufactured on the substrates with chemically-etched nano-scale surface formations that are responsible for a clearly marked luminescence band located at the energy exceeding the band gap of the bulk GaP. The other peculiarity produced by surface patterning concerns a remarkable redshift of material's optical absorption edge. At the room temperature, the height of potential barrier for Ni–GaP structure is 1.8 eV, with the monochromatic sensitivity peaking at 0.35 A/W. The comparative study of diode performance under different light sources exhibited the pronounced linear photocurrent-illumination dependence for about five orders of illumination magnitude, evidencing good optical and electrical quality of Ni–GaP diodes with surface-modified semiconductor substrate.     

a-Si/SiN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> multilayered light absorber for solar cell

40 alternate a-Si/SiN _x multilayer are incorporated as an absorber layer in a p–i–n solar cell. The device is fabricated using hot-wire chemical vapor deposition (HWCVD) technique. The structure of the multilayer film is examined by high resolution transmission electron microscopy (HR-TEM) which shows distinct formation of alternate a-Si and SiN _x layers. The a-Si and SiN _x layers have thickness of ~3.5 and 4 nm, respectively. The photoluminescence (PL) of multilayer film shows bandgap energy of ~2.52 eV, is larger than that of the c-Si and a-Si. Dark and illuminated current–voltage (I–V) characterization of the ML films shows that these ML are photosensitive. In the present work, it is seen that the p–i–n structure with i-layer as ML quantum well (QW) structures show photovoltaic effect with relatively high open-circuit voltage (V _OC). The increment of bandgap energy in PL and high V _OC of the device is attributed to the quantum confinement effect (QCE).     

Synthesis and optical properties of nanocrystalline ZnO powders prepared by a direct thermal decomposition route

This paper reports the synthesis and optical properties of nanocrystalline ZnO powders with crystallite sizes of 32.5 (±1.4)–43.4 (±0.4) nm prepared by a direct thermal decomposition of zinc acetate at the temperatures of 400, 500, 600, and 700°C for 4 h. The structure of the prepared samples was studied by XRD and FTIR spectroscopy, confirming the formation of wurtzite structure. The morphology of the samples revealed by SEM was affected by the thermal decomposition temperature, causing the formations of both nanoparticles and nanorods with different size and shape in the samples. The synthesized powders exhibited the UV absorption below 400 nm (3.10 eV) with a well defined absorption peak at around 285 nm (4.35 eV). The estimated direct bandgaps were obtained to be 3.19, 3.16, 3.14, and 3.13 eV for the ZnO samples thermally decomposed at 400, 500, 600, and 700°C, respectively. All the samples exhibited room-temperature photoluminescence (PL) showing a strong UV emission band at ∼395 nm (3.14 eV), a weak blue band at ∼420 nm (2.95 eV), a blue–green band at ∼485 nm (2.56 eV), and a very weak green band at ∼529 nm (2.35 eV). The mechanisms responsible for photoluminescence of the samples are discussed.     

Laser initiation of a mixture of PETN with NiC nanoparticles at elevated temperatures

The temperature dependence of the probability of the explosion of pentaerythritol tetranitrate (PETN) with an admixture of NiC particles (0.3 wt %) initiated by laser pulses (1064 nm, 20 ns) was studied over the temperature range 295–450 K. At 295–350 K, a weak temperature dependence was observed. The determining contribution to explosion initiation was made by the absorption of laser radiation by nanoparticles. The threshold of explosive decomposition at 295 K decreased by ∼40 times compared with samples free of NiC nanoparticles. Over the temperature range 400–450 K, the threshold of the explosive decomposition of samples containing NiC nanoparticles decreased with the activation energy ∼0.4 eV. A decrease in the threshold of explosive decomposition with a ∼0.4 eV activation energy over the temperature range 340–440 K was also observed for laser action on PETN samples not containing NiC. A hypothesis was suggested according to which the absorption of a light quantum caused the transfer of an electron from the valence band of the crystal to a level in the forbidden band with subsequent thermal positive ion dissociation to the carbocation and NO₃ radical.     

Preparation and Time-Resolved Luminescence Bioassay Application of Multicolor Luminescent Lanthanide Nanoparticles

Because highly luminescent lanthanide compounds are limited to Eu³⁺ and Tb³⁺ compounds with red (Eu, ~615 nm) and green (Tb, ~545 nm) emission colors, the development and application of time-resolved luminescence bioassay technique using lanthanide-based multicolor luminescent biolabels have rarely been investigated. In this work, a series of lanthanide complexes covalently bound silica nanoparticles with an excitation maximum wavelength at 335 nm and red, orange, yellow and green emission colors has been prepared by co-binding different molar ratios of luminescent Eu³⁺–Tb³⁺ complexes with a ligand N,N,N¹,N¹-(4′-phenyl-2,2′:6′,2′′-terpyridine-6,6′′-diyl)bis(methylenenitrilo) tetrakis (acetic acid) inside the silica nanoparticles. The nanoparticles characterized by transmission electron microscopy and luminescence spectroscopy methods were used for streptavidin labeling, and time-resolved fluoroimmunoassay (TR-FIA) of human prostate-specific antigen (PSA) as well as time-resolved luminescence imaging detection of an environmental pathogen, Giardia lamblia. The results demonstrated the utility of the new multicolor luminescent lanthanide nanoparticles for time-resolved luminescence bioassays.     

Preparation of a Superparamagnetic Nanocomposite with a High Content of Magnetic Iron Oxide in a PMMA Matrix by Precipitation Polymerization

We have prepared nanocomposites containing large amounts of superparamagnetic nanoparticles dispersed in a polymethyl methacrylate matrix. The preparation was divided into three steps. In the first step, maghemite nanoparticles were synthesized using coprecipitation from aqueous solutions, followed by coating with oleic acid (OA). In the second step, the OA-coated nanoparticles were dispersed in n-decane to prepare a stable, concentrated suspension. Finally, methyl methacrylate was added to the suspension and in situ polymerization was carried out at elevated temperatures. The content of nanoparticles was controlled by varying the nanoparticles/monomer ratio. The main focus was on controlling the nanocomposite's homogeneity. The nanocomposites were characterized using X-ray powder diffractometry, TEM, SEM, thermogravimetry, FT-IR, NMR and magnetic measurements. The TEM analysis showed that the nanoparticles were well dispersed in the polymer matrix. They retained their superparamagnetic nature even when encapsulated by polymer with concentrations up to 48 wt%. The high loading of magnetic nanoparticles resulted in relatively high saturation magnetizations of the nanocomposites, up to 31 emu/g.     

Luminescence of CaGa<Subscript>2</Subscript>Se<Subscript>4</Subscript>:Eu crystals

We have studied photoluminescence and thermoluminescence (PL and TL) in CaGa₂Se₄:Eu crystals in the temperature range 77–400 K. We have established that broadband photoluminescence with maximum at 571 nm is due to intracenter transitions 4f⁶ 5d–4f⁷ (⁸S_7/2) of the Eu²⁺ ions. From the temperature dependence of the intensity (log I–10³/T), we determined the activation energy (E _a = 0.04 eV) for thermal quenching of photoluminescence. From the thermoluminescence spectra, we determined the trap depths: 0.31, 0.44, 0.53, 0.59 eV. The lifetime of the excited state 4f6 5d of the Eu²⁺ ions in the CaGa₂Se₄ crystal found from the luminescence decay kinetics is 3.8 μsec. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 112–116, January–February, 2009.     

A hybrid electrochemical–thermal method for the preparation of large ZnO nanoparticles

A simple and efficient two-step hybrid electrochemical–thermal route was developed for the synthesis of large quantity of ZnO nanoparticles using aqueous sodium bicarbonate electrolyte and sacrificial Zn anode and cathode in an undivided cell under galvanostatic mode at room temperature. The bath concentration and current density were varied from 30 to 120 mmol and 0.05 to 1.5 A/dm². The electrochemically generated precursor was calcined for an hour at different range of temperature from 140 to 600 °C. The calcined samples were characterized by XRD, SEM/EDX, TEM, TG-DTA, FT-IR, and UV–Vis spectral methods. Rietveld refinement of X-ray data indicates that the calcined compound exhibits hexagonal (Wurtzite) structure with space group of P63mc (No. 186). The crystallite sizes were in the range of 22–75 nm based on Debye–Scherrer equation. The TEM results reveal that the particle sizes were in the order of 30–40 nm. The blue shift was noticed in UV–Vis absorption spectra, the band gaps were found to be 5.40–5.11 eV. Scanning electron micrographs suggest that all the samples were randomly oriented granular morphology.