Synthesis and characterization of bismuth doped barium sulphide nanoparticles

We have synthesized BaS:Bi nanocrystalline powder of average grain size 35 nm by solid-state diffusion method using sodium thiosulphate as a flux. During this work we have optimized the nature and amount of flux, amount of the dopant and temperature of firing for maximum yield of photoluminescence. The samples were characterized by X-ray powder diffraction (XRD) method, transmission electron microscopy (TEM), photoluminescence (PL) and UV-visible techniques. On excitation by 425 nm, these nanophosphors give one emission peak at 575 nm which corresponds to green color. In the excitation spectra of these particles there are two peaks at 350 nm and 425 nm. The effect of dopant concentration on the photoluminescence of BaS:Bi nanocrystallites has been studied which is in agreement with the principle of concentration quenching. The energy band gap of bismuth doped BaS nanopowder has been calculated to be 4.25 eV and is blue shifted in comparison to their bulk counterparts. The blue shift may be due to the quantum confinement in the particles.     

Synthesis and luminescence properties of europium doped silica thin film

Mixture of europium oxide (Eu₂O₃) nanoparticles and spin-on glass (SOG) solution without annealing exhibited a strong room temperature photoluminescence (PL) at 610 nm. We developed a one-step synthesis to incorporate europium ions in silica thin film by mixing the Eu₂O₃ nanoparticles with the SOG solution and found that the weight ratio of the nanoparticles and the SOG solution was 1:5 for maximum PL. We also studied the temperature effect on the light emission of the europium doped thin film by time-of-flight secondary ion mass spectrometry (SIMS). The PL intensity of the thin film doubled after annealing. SIMS study confirmed the reduction of hydroxyl groups and explained the PL enhancement in the annealed europium doped silica thin film.     

Synthesis and characterization of cadmium doped lead-borate glasses

Cadmium doped lead-borate glasses were prepared from the melts in appropriate proportions of PbO₂, H₃BO₃ and (15–40 mol%) CdO mixture in the temperature range 700–950°C. The infrared spectra of the glasses in the range 400–4000 cm^-1 show their structures. No boroxol ring formation was observed in the structure of these glasses. Furthermore, doped cadmium atoms were not seen in tetrahedral coordination. But the conversion of three-fold to four-fold coordination of boron atoms in the structure of glasses was observed.     

Shape control of doped semiconductor nanocrystals (d-dots)

Formation of Mn²⁺-doped ZnSe quantum dots (Mn:ZnSe d-dots) with both branched and nearly spherical shapes has been studied. Structure analysis indicates that the Mn²⁺ dopants were localized in the core of a branched nanocrystal. The growth of branched d-dots, rather than spherical ones, was achieved by simply varying the concentration of two organic additives, fatty acids, and fatty amines. The photoluminescence properties of the branched nanocrystals were explored and compared with those of the nearly spherical particles. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Synthesis and optical properties of a lithium niobiosilicate glass doped with europium

The sol–gel method was used to prepare a lithium niobiosilicate glass doped with europium ions, 91SiO₂–4Li₂O–4Nb₂O₅–1Eu₂O₃ (% mole). The dried gel was heat-treated between 500 °C and 750 °C and glass ceramics were obtained. X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman studies show that crystallization starts at temperatures above 600 °C. The LiNbO₃ and EuNbO₄ nanocrystals were found in the heat-treated samples as corroborated by the structural, morphological and optical properties. Room temperature photoluminescence (PL) studies allow us the identification of multiple Eu-related optical centres and the strongest red ⁵D₀ → ⁷F₂ intraionic transitions occur in the samples heat-treated at 600 °C where the LiNbO₃ crystal phase was detected.     

Synthesis and study of organically capped ultra small clusters of cadmium sulphide

Ultra small clusters of cadmium sulphide are synthesized using non-aqueous and aqueous chemical methods. Thiophenol has been used as a capping agent for non-aqueous synthesis whereas various reagents such as mercaptoethanol, hexametaphosphate, ethylene glycol and ethanol have been used as additives for an aqueous method of synthesis. Properties of the clusters synthesized are discussed based on optical absorption, X-ray diffraction, transmission electron diffraction and photoelectron spectroscopy. Particles as small as 0.7 nm diameter could be synthesized with thiophenol and mercaptoethanol as additives. The effect of varying the molarities of the different additives on the properties of the CdS nanoclusters synthesized are discussed. Systematic ageing studies of the nanoclusters showed that larger particles age faster than the smaller clusters. Ageing also leads to better crystallization of the particles. It has been observed that the smallest particles (0.7 nm diameter) possess tetrahedrally bonded fragments of CdS and intercluster structural long range order does not exist. However, bigger particles (2.0 nm diameter) show bulk cubic structure. X-ray photoelectron spectroscopy studies have been done to study the purity and stoichiometry of the clusters synthesized and strongly support the existing proposal of the formation and stability of CdS nanoclusters.     

Synthesis,characterization and optical properties of bismuth germanate doped with trivalent europium

Bismuth germanate single crystals doped with trivalent europium were grown by the Czochralski method. Procedures and results of synthesis experiments are reported. Microprobe analysis reveals the segregation of doped rare-earth elements. Spectroscopic studies of Eu³⁺ ions suggests C_3v point symmetry for the cationic site. Oscillator strengths and τ_λ parameters for Eu³⁺ were calculated.     

Synthesis and spectroscopic study of lutetium pyrosilicate single crystals doped with trivalent europium

Lutetium pyrosilicate single crystals Lu_2?xEu_xSi₂O₇ were grown by a floating zone technique associated with an arc image furnace. Procedures and results of synthesis and characterisation experiments are reported. Vibrational investigation of Lu₂Si₂O₇ allows complete attribution of internal and external modes in good agreement with group theory predictions. Spectroscopic studies of Eu³⁺ ions confirm C₂ point symmetry for the cationic site. Oscillator strengths and $\text{Ω}{}_{\mathrm{\lambda }}$ parameters for Eu³⁺ were calculated.     

Synthesis of Mn doped ZnO nanocrystals by solvothermal route and its characterization

Undoped and Manganese doped Zinc Oxide were prepared by solvothermal technique. The structural analysis was carried out using X-ray diffraction. It showed that the undoped Zinc Oxide and Manganese doped Zinc Oxide nanocrystals to exhibit hexagonal wurtzite structure. Grain sizes were estimated from Atomic Force Microscopy and Transmission Electron Microscopy images. The surface morphological studies from Scanning Electron Microscope, Transmission Electron Microscope and Atomic Force Microscope depicted spherical particles with formation of clusters. The magnetic behavior studied by Vibrating Sample Magnetometer indicated paramagnetic behaviour. Hyperfine splitting is observed using Electron Spin Resonance studies.     

Photoluminescence of cubic BN doped with europium and codoped with europium and chromium

We have prepared cubic boron nitride samples doped with europium and codoped with europium and chromium. Their red photoluminescence is due to Eu³⁺ and Eu³⁺-Cr³⁺ electronic transitions involving Eu³⁺ in a noncentrosymmetric position in a field of cubic symmetry. Chromium is shown to have a positive effect on the incorporation of Eu³⁺ into lattice sites of c-BN. The photoluminescence spectrum of polycrystalline c-BN codoped with Eu³⁺ and Cr³⁺ is a combination of the spectra of Eu³⁺ in fields of cubic and monoclinic symmetries, the latter spectrum being blue-shifted relative to the spectrum of Eu³⁺-doped microcrystalline powder. The c-BN materials prepared in this study can be used as red phosphors and light emitters possessing high thermal stability, radiation hardness, and chemical resistance.     

Quantification of the morphological transition in cadmium selenide nanocrystals as a function of reaction temperature

Controlling the morphology of semiconductor nanocrystals has typically relied on controlling the concentration and species of surface ligands utilized in synthesis. Specific shapes, such as branched structures are of particular interest as the light harvesting and charge separating layer in a photovoltaic device. In this work we quantify how changes in the reaction temperature affect the resulting morphology of the nanocrystals. The narrowness of the temperature range over which the morphological transition occurred provides guidance to the tolerances necessary in the synthesis of CdSe utilized in commercial devices on a large scale.     

Synthesis and photoluminescent properties of doped ZnS nanocrystals capped by poly(vinylpyrrolidone)

Zinc sulfide semiconductor nanocrystals doped with selected transition metal ions (Mn²⁺, Cu²⁺, and Ni²⁺) have been synthesized via a solution-based method utilizing low dopant concentrations (0–1%) and employing poly(vinylpyrrolidone) (PVP) as a capping agent. UV/Vis absorbance spectra for all of the synthesized nanocrystals show an exitonic peak at around 310 nm, indicating that the introduction of the dopant does not influence the particle size. Calculated particle sizes for undoped and doped nanocrystals are in the 4.3 nm size range. Photoluminescence spectra recorded for undoped ZnS nanocrystals, using an excitation wavelength of 310 nm, exhibit an emission peak centered at around 460 nm. When a dopant ion is included in the synthesis, peaks in the corresponding photoluminescence spectra are red-shifted. For Mn-doped nanocrystals, an intense peak centered at approximately 590 nm is found and is seen to increase in photoluminescence intensity with an increase in dopant concentration. In contrast, for Cu-doped and Ni-doped nanocrystals, weaker peaks centered at around 520 and 500 nm, respectively, are observed and are noticed to decrease in photoluminescence intensity with an increase in dopant concentration. These results clearly show that careful control of synthetic conditions must be employed in the synthesis of doped semiconductor nanocrystals in order to obtain materials with optimized properties.     

Synthesis and microstructural control of flower-like cadmium germanate

Flower-like Cd₂Ge₂O₆ have been synthesized using a facile hydrothermal process with ethylenediamine. The roles of hydrothermal conditions on the size and morphology of the flower-like Cd₂Ge₂O₆ were investigated. The research results show that the obtained Cd₂Ge₂O₆ presents a flower-like microstructures composed by radial nanorods with diameter of 50–100 nm and length of 0.5–2 μm, respectively. The formation mechanism of the flower-like Cd₂Ge₂O₆ is explained according to the ethylenediamine-assisted nucleation-“Ostwald ripening” process.     

Synthesis and spectral properties of colloidal Nd doped NaYF4 nanocrystals

Transparent, chloroform dispersed α-NaYF₄ nanocrystals doped with neodymium ions were synthesized and characterized. XRD and TEM measurement confirmed cubic structure of α-NaYF₄ of the nanoparticles (NPs). The absorption and emission spectra as well as ⁴F_3/2 level fluorescence decay curves were measured in order to estimate the influence of Nd³⁺ concentration in the matrix on the optical properties of the NPs. With the increase of Nd³⁺ doping level, the Judd-Ofelt Ω₄ parameter as well as the spectroscopic Nd³⁺ parameter X_Nd = Ω₄/Ω₆ was growing. In the same time the Ω₂ and Ω₆ were decreasing. Theoretical luminescence lifetimes of the ⁴F_3/2 level equal to ∼300 μs were also calculated and compared with the experimental values to quantify the concentration quenching. Based on this comparison, quantum efficiency was found to vary systematically between ∼100% and 4% for Nd³⁺ content increasing from 2 up to 25%.     

Trap diagnostic of thin cadmium sulphide films

A simplified expression for the temperature dependence of trap depth was derived. This expression together with experimental observations confirmed the existence of a number of deep trap levels (0.9–1.02 eV) in CdS and it is suggested that with the knowledge of these trap levels a better correlation between experimental and theoretical results for tunnel-induced impact ionization is possible.