Influence of Synthesis Temperature on the Structural, Morphological and Optical Properties of MoO3 Nanorods.

Molybdenum trioxide nanomaterials have attained notable attention in the recent past and are used in various optoelectronic and biomedical applications. Here blue and purple blue light emitting MoO3 nanophosphors were synthesized using the simple hydrothermal method at three different temperatures 100ºC, 150°C, and 200°C. Structural characterization using XRD along with Raman spectroscopy confirms the formation of a highly stable orthorhombic phase. Micro strain effects have been analyzed by employing the Williamson-Hall method using a uniform deformation model. Nanorod like morphology was obtained from FESEM. Optical analysis, using Tauc plot shows a decreasing trend in bandgap value with increasing temperature. Emission peaks in the photoluminescence spectrum are associated with the transition between the sub-bands of the Mo5+ defect state. From CIE coordinates it is confirmed that the characteristic light from the samples is blue and purple-blue. Being an excellent blue and purple blue light emitting phosphor, MoO3 is a suitable material for future LED and fluorescence imaging applications.

Synthesis and Characterisation of SrAl2O4: Eu3+ Orange-Red Emitting Nanoparticles.

The current study involves the synthesis and characterisation of europium doped strontium aluminate nanophosphors using the solid-state reaction method with varying concentrations of europium. The existence of the SrAl2O4 phase in all samples was verified using X-ray diffraction and FTIR analysis. The lattice parameters as well as phase fractions were determined using Rietveld refinement. Surface morphology was studied using field emission scanning electron microscope. Using the Tauc plot method acquired from the diffuse reflectance spectra, the band gaps of the samples were determined and it was found that the doped samples possess lower band gaps compared to the host. Our findings demonstrate that these nanophosphors exhibiting bright orange-red emission under UV excitation with quantum efficiency 70.68%, can be applied for display and fluorescence imaging.

Effect of Dopant Precursor Solutions on the Structural and Optical Properties of ZnS:Cu Nanophosphors.

Nanoparticles of ZnS doped with Cu (ZnS:Cu) were prepared at room temperature by wet chemical method without any capping agent using two dopant precursor solutions-aqueous: (i) Copper acetate [ZnS:CA] and (ii) Copper nitrate [ZnS:CN] solutions. The characterization of the samples was carried out for the structural, surface morphological and optical properties. XRD analysis results revealed the formation of cubic structure ZnS:Cu particles with an average size of 2.5 nm. From diffuse reflectance spectral (DRS) studies the band gap was found to be higher than bulk due to quantum confinement effect. In Photoluminescence (PL) spectra a sulphur vacancy related blue emission around 432 nm and a green emission from the recombination between the shallow donor level and the t2 level of Cu were observed. The ZnS:CN nanoparticles showed enhanced luminescence property compared with that of ZnS:CA nanoparticles.

Intense Yellow Emitting Biocompatible CaS:Eu Nanophosphors Synthesized by Wet Chemical Method.

Here we report the synthesis of intense yellow emitting CaS:Eu nanoparticles by a low temperature wet chemical coprecipitation method which can be used for various optoelectronic and biological applications. The particles were characterized systematically using techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy, photoluminescence (PL) and UV-Vis absorption spectroscopy. XRD analysis revealed that all the samples exhibited a cubic structure with good crystallinity. Formation of nanoparticles having spherical morphology with the diameter in the range 4-8 nm was confirmed by TEM analysis. The PL emission color varied from yellowish white to yellow as the excitation wavelength was increased from 335 to 395 nm. The PL emission peaks are attributed to 5D0- 7FJ (J = 0,1,2,3,...) electronic transitions of Eu3+ ions incorporated into the CaS host lattice. Fourier transform infrared spectroscopy measurements were taken to elucidate the presence of various bonds in the sample. In vitro cytotoxicity analysis of the samples was also performed using MTT assay on human L929 fibroblasts cell lines in order to assess the biocompatibility of the nanoparticles. This is the first time report of the cytotoxicity studies of highly fluorescent CaS: Eu nanoparticles synthesized by wet chemical method.

Impact of activator incorporation on red emitting rods of ZnGa2O4:Cr3+ phosphor.

Chromium doped zinc gallium oxide (ZnGa2O4:Cr3+) microrods were synthesized by simple solid state reaction method. The transformation on crystal structure and optical properties with molar concentration of Cr3+ were analyzed. The cubic spinel nature of ZnGa2O4:Cr3+phosphor and their crystalline nature were confirmed from x- ray diffractogram. The average grain size of the samples range between 24 and 29 nm, with lattice parameter values greater than that of bulk. Lattice strain produced in the lattice on doping was estimated from the Williamson-Hall plot. It increases on Cr3+ doping up to 3 mol% and then decreases. Rod like nature of zinc gallate was observed from the surface morphological analysis using SEM. X-ray photoelectron spectroscopy was used for the chemical state identification of the constituent elements in the compound. The photoluminescense spectra consists of various emission lines originated from the chromium ion in the spinel lattice. The purity of red emissions were observed from chromaticity diagram with a concentration quenching initiated from the dipole-dipole interaction, with increase in dopant concentration. Band gap of the samples were estimated using Kubelka-Munk equation which exhibited red shift compared to bulk due to band tailing effect.

Green Emitting Cerium Doped CaS Whiskers Grown by Solid State Diffusion Method.

Undoped and cerium doped Calcium sulfide (CaS) phosphors were synthesized using solid state diffusion method. The X-ray diffraction pattern revealed that both undoped and doped CaS crystallites have cubic structure with average crystallite size varying from 20 to 30 nm. Scanning electron micrographs indicated that Ce doped CaS phosphors were composed of whiskers with different dimensions and orientations. The optical properties of undoped and Ce doped particles were characterized using Photoluminescence (PL) and UV-Vis absorption spectroscopy. The PL emission spectrum of cerium doped CaS phosphors for an excitation wavelength 465 nm showed a main peak at 500 nm and a shoulder peak at 556 nm due to 5d → 4f transition in Ce3+ ions. The variation of PL intensity with cerium concentration was investigated and the maximum PL intensity was obtained for a doping concentration of 3 wt.%. The optical band gap of the samples was estimated from the diffuse reflectance spectrum and was found to increase with increase in cerium concentration. The enhanced optical properties of these phosphors can be exploited in various optoelectronic devices including displays and bioimaging techniques.

Wet chemical synthesis of chitosan capped ZnO:Na nanoparticles for luminescence applications.

The structural and optical properties of nanomaterials exhibit severe changes when capped with organic polymers. In this work we focus on the effect of chitosan capping on ZnO:Na nanoparticles synthesized by wet chemical method. The main characteristics analyzed are x-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and photoluminescence (PL). Hexagonal crystal formation of nanoparticles was confirmed from the XRD and the lattice strain was estimated from the Williamson Hall (WH) plot. Various bonds present in the synthesized sample were analyzed using FTIR. Capping results in the reduction in grain size thereby enhancement in the PL intensity. The yellow emission is in well agreement with the Commission International d'Eclairage (CIE) diagram.

Structural and Optical Properties of White Light Emitting ZnS:Mn(2+) Nanoparticles at Different Synthesis Temperatures.

We report of the synthesis and characterisation of white emitting ZnS:Mn(2+) nanoparticles. The spectroscopic properties and the crystal structure of Mn doped ZnS nanoparticles are studied here to provide a better understanding on how the luminescence emission and the crystalline composition are influenced by the synthesis temperature. The synthesis of the samples were carried out by the simple wet chemical precipitation method. The influence of synthesis temperature on structure and optical properties were studied at constant Mn concentration. The nanoparticles were structurally characterized by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The XRD studies show the phase singularity of Mn doped ZnS particles having zinc-blende (cubic) structure at all temperatures. The band gap of the doped samples are red shifted with temperature. Electron Paramagnetic Resonance (EPR) spectra exhibited resonance signals, characteristic of Mn(2+). Incorporation of Mn in the ZnS nanoparticles was confirmed by Inductively Coupled Plasma- Atomic Emission Spectroscopic studies (ICP-AES). The samples show an efficient emission of yellow-orange light centred at 590 nm which is characteristic of Mn(2+) along with a blue emission at 435 nm due to sulfur vacancy. The overall emission is white at all temperatures with CIE co-ordinates in close agreement with achromatic white.

Photoluminescence of nanocrystalline ZnS thin film grown by sol-gel method.

Nano and polycrystalline ZnS thin films play a crucial role in photovoltaic technology and optoelectronic devices. In this work, we report the photoluminescence (PL) characterization of nanocrystalline ZnS thin films synthesized by dip coating method. The PL spectra exhibit broad nature with multiple emission peaks which are due to the different defect levels in the prepared film.

The photoluminescence of SrS:Cu nanophosphor.

Strontium sulfide doped with copper has been regarded as one of the most promising inorganic materials for the blue-green color phosphor. A wet chemical precipitation method with post-annealing is presented for the synthesis of copper-doped SrS nanoparticles. XRD studies revealed the phase purity of SrS particles with rocksalt structure. TEM images showed the formation of nanoparticles with an average size of 7 nm. Green photoluminescence emission (PL) at 535 nm was observed for an excitation wavelength of 356 nm, the intensity of which was greater than that of coarser phosphor particles synthesized by solid state reaction. Low temperature PL showed a redshift with decreasing temperature which is due to aggregated copper centers. Luminescent decay at room temperature was found to be faster than the reported values of the corresponding transition in thin film samples. A blueshift in the absorption edge was observed for the nanophosphor with respect to the bulk due to reduction in particle size.