Photoluminescence Spectral Analysis Research Articles

Crystal structure and photoluminescent properties of BaZn1−xEuxV2O7 nanoparticles

The structure of novel BaZn1−xEuxV2O7 nanoparticles (synthesised employing solution combustion process) was refined and determined from X-ray diffraction (XRD) profiles by the Rietveld refinement method. It was found to crystallize in orthorhombic lattice with the Pnma space group. Further structural informations and particle morphology were investigated using FT-IR spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photoluminescence spectral analysis showed that these nanophosphor can be effectively excited by near-UV light (305 nm, 395 nm), emitting intense red luminescence (620 nm) corresponding to the hypersensitive 5D0→7F2 transition of Eu3+ ion, located at low-symmetry site with no inversion center in BaZnV2O7 crystal lattice. The dependence of luminescence intensity and chromaticity index on Zn2+ substitution by Eu3+ ions in BaZnV2O7 was also investigated which unveil 5 mol% as the optimum concentration. These nanophosphors are potential candidate for white LEDs using near ultra-violet (NUV) LED chip excitation.

White light generation in Ce3+[sbnd]Tb3+[sbnd]Sm3+ codoped oxyfluoroborate glasses

Ce3+, Tb3+and Sm3+ oxyfluoroborate glasses were prepared and characterized using absorption, photoluminescence and time decay spectral analysis respectively. The decrease of emission peak intensity and lifetime values of Ce3+ ions are observed by introducing Tb3+ and Sm3+ into glass. This is due to an efficient energy transfer from Ce3+ to Tb3+, Sm3+; Tb3+ to Sm3+ and cross-relaxation channels. Further, the important characteristic parameters of white light emitting materials viz., energy transfer efficiency, chromaticity color coordinates, correlated color temperature and color purity are evaluated.

Preparation by a facile method and characterization of amorphous and crystalline nickel sulfide nanophases

Abstract A simple solvothermal route using a domestic microwave oven has been developed to prepare the prominent nickel sulfide nanophases (amorphous NiS, and crystalline NiS 1.03 , β-NiS and α-NiS). The prepared nanophases have been characterized chemically, structurally, optically, electrically, and magnetically by the available methods like thermogravimetric and differential thermal analyses, X-ray powder diffraction analysis, scanning electron microscopic, and transmission electron microscopic analyses, energy dispersive X-ray spectroscopic, Fourier transform-infrared spectral, UV–Vis spectral and photoluminescence spectral analyses, AC and DC electrical measurements at various temperatures in the range 40–150 °C, and vibrating sample magnetometric measurements. The average particle sizes obtained through transmission electron microscopic analysis are 15, 17, 18, 20 nm respectively for the amorphous NiS, NiS 1.03 , β-NiS and α-NiS nanophases. Results obtained in the present study indicates that the method adopted is found to be an effective and economical one for preparing these nanophases with high purity, reduced size, homogeneity, and useful optical, electrical and magnetic properties.

Interstitial Defects Induced Ferroelectricity in Undoped ZnO Nanorods at Room Temperature

A simple approach for obtaining room temperature ferroelectricity in ZnO rod structures at the nanoscale is reported. A systematic comparative study between two kinds of nanorods prepared by different processes reveals the physics behind it. It is observed that ZnO nanorods grown (in-situ) by a sol gel method on platinum substrate show ferroelectric behaviour. On the contrary, ZnO nanorods first grown by a sol gel method and then spin-coated on a platinum substrate (ex-situ) do not demonstrate this kind of feature. X-ray diffraction analysis confirms partially (002) and (100) plane oriented growth of both samples. From photoluminescence (PL) spectral analysis it is interpreted that oxygen vacancies/zinc interstitial defects, which arises from the large lattice mismatch between the Pt substrate and the ZnO nanorods grown thereon, and preferential ZnO growth along 002], can be causes of this type of phenomena. C-V characterization, P-E hysteresis loop along with piezoelectric force microscopy support this observation.

Identification of the crystallographic sites of Eu2+ in Ca9NaMg(PO4)7: structure and luminescence properties study

The substituted activator ions Eu(2+) in the β-Ca3(PO4)2-type structure, Ca9NaMg(PO4)7 compound, have been studied as emission centers, as well as structural probes. The crystal structure and crystallographic sites of Eu(2+) in Ca9NaMg(PO4)7 have been identified by Rietveld refinements, electron paramagnetic resonance (EPR) spectroscopy analysis and combined photoluminescence spectral analysis, respectively. Ca9NaMg(PO4)7:Eu(2+) phosphor exhibits a broad emission band in the visible light region with three distinguished peaks centered at 415, 458, and 615 nm, which are ascribed to different Eu(2+) emission centers occupied in three different Ca crystallographic sites. The concentration quenching behavior, variation in lifetimes and the temperature dependent luminescence properties have been investigated as a function of different emission centers, 415, 458, and 625 nm for Ca9NaMg(PO4)7:Eu(2+) phosphor. Accordingly, the relationship among three different Eu(2+) luminescence centers originating from three different Ca(2+) crystallographic sites has been found and verified.

Crystal Growth, Spectral, Thermal and Optical Properties of Phthalic Anhydride (PA) Single Crystal

ABSTRACT Organic single crystal of Phthalic Anhydride (PA) was successfully grown by slow evaporation method. The structure of the grown crystal was confirmed by X-ray diffraction analysis. FT-IR, and FT-Raman spectral analysis of the crystalline samples reveal that the crystalline sample consists of all functional groups. The placement of protons was identified from H1-NMR spectral analysis. UV-Visible and photoluminescence spectral analyses were carried out for the grown crystals. The thermal behavior was studied with TGA-DTA analyses. The existence of second harmonic generation (SHG) signal was observed using Nd:YAG laser with a fundamental wavelength of 1064 nm. Keywords: Organic crystals, NLO crystals

Raman and Photoluminescence Spectroscopy of Nanocrystalline Diamond Films Grown by Hot Filament CVD

Nanocrystalline diamond films were grown by hot filament chemical vapour deposition (HFCVD) in a mixture of methane and hydrogen gases. Three straight parallel wires filament configuration were used in the HFCVD system for the deposition of the films studied in this work. The deposition pressure for the growth of diamond films in this hot filament chemical vapour deposition (HFCVD) reactor have been optimized to be at 20 torr with the methane and hydrogen flow-rates fixed at 2 and 200 sccm respectively. The films studied in this work were grown at low deposition pressures of 2 and 5 torr using the same gas flow-rates used for the optimized diamond film growth including an additional film grown at pressure of 5 mbar with the methane flow-rate reduced to 1 sccm. The morphology showed the formation of closed packed diamond grains for the film grown at 5 torr with methane and hydrogen flow-rates fixed at 2 and 200 sccm. Decrease in pressure and methane flow-rate produced significant changes to the morphology of the diamond grains formed. X-ray diffraction showed that diamond phase phases were dominant in the films deposited at higher pressure. Raman and photoluminescence (PL) spectral analysis were performed using spectra acquired at 325 and 514 nm excitation energies. Raman analysis revealed that increase in deposition pressure from 2 to 5 Torr resulted in the transformation of the film structure from diamond-like-carbon to nanocrystalline diamond structure. UV excitation produced high PL emission intensity at 2.1 eV and the PL intensity was highest for the films deposited at the lowest pressure. Visible excitation on the other hand produced low intensity broad PL emission for all the films between 1.2 and 2.5 eV and the PL intensity was high for the films deposited at the highest deposition pressure.

Enhanced photocatalytic cytotoxic activity of Ag@Fe-doped TiO2 nanocomposites against human epithelial carcinoma cells

Fe-doped TiO2 nanopowders with controlled molar-atomic ratios of iron to titanium oxide (in percentage) ranging from nominal 1 to 10% were synthesized by a new simple sol–gel method. Metallic Ag nanoparticles were successfully deposited on the nanopowder of the Fe-doped TiO2 surface by citrate reduction of AgNO3 in water/CH3CN mixture. The molar ratio of iron to TiO2, phase formation, bandgaps, crystallinity, catalytic and plasmonic properties of the resultant composites were systematically investigated using UV-visible spectroscopy, SEM, TEM, XRD, XPS, EDX, and photoluminescence spectral analyses. The photocatalytic activity of Ag@Fe-doped TiO2 composite nanoclusters was evaluated through photocatalytic killing of cancer cells. For the photocatalytic killing of cancer cells under visible light irradiation, as-prepared Ag@Fe-doped TiO2 nanopowders exhibited higher activity than Fe-doped TiO2. The promoting effect of the Ag nanoparticles deposited on the Fe-doped TiO2 surface showed strong absorption in the visible region due to localized surface plasmon resonance of Ag and inhibited the recombination of photoelectrons and holes rather than only Fe-doped TiO2. The cytotoxic cell killing efficiency depends on the molar ratio of Fe content to TiO2. The optimum Fe content in Fe-doped TiO2 was determined to be 5% due to the Fe/TiO2 molar ratio. Based on the obtained results, a plausible mechanism was also proposed.

Transparent luminescent bulk nanocomposites of polysiloxane embedded with CdS nanocrystallines by a direct dispersion process

Transparent luminescent bulk nanocomposites of polysiloxane (PSO) embedded with semiconductor nanocrystals (NCs) have been fabricated by the direct dispersion of CdS NCs in alkyl-(poly)siloxane (APS) followed by co-polymerization. The non-polar characteristics of the APS precursor are compatible with the CdS NC surface (oleylamine), which allows the direct dispersion of the CdS NCs without the need of any surfactant exchange. Chemical crosslinking of the NC-APS dispersion via hydrosilylation between Si-H and the vinyl group in APS immobilizes the CdS NCs in the polysiloxane network. Net-shaped three-dimensional bulk transparent polysiloxane/CdS NC composites were obtained by liquid casting of the NC-precursor dispersion and chemical crosslinking. The PSO/CdS NC composites show visible luminescence under ultraviolet excitation and the luminescent color is tunable from blue to red by controlling the NC concentration in the composite. Photoluminescence spectral analyses reveal the origin of the luminescence as being from the defect emission of the CdS NCs (550-900 nm) and an emission from the PSO matrix (380-550 nm). The luminescent spectra covered a wide range from the ultraviolet to the near-infrared region. The luminescence of the PSO/CdS NC nanocomposites was stable without any apparent degradation after exposure to air for a long time. This simple direct dispersion process is feasible for the fabrication of luminescent nanocomposites with useful optical properties for potential applications in optics and photoelectron devices.

Systematic First Principles Calculations of the Effects of Stacking Fault Defects on the 4H-SiC Band Structure

Shockley-type Stacking faults (SSF) in hexagonal Silicon Carbide polytypes have received considerable attention in recent years since it has been found that these defects are responsible for the degradation of forward I-V characteristics in p-i-n diodes. In order to extend the knowledge on these kind of defects and theoretically support experimental findings (specifically, photoluminescence spectral analysis), we have determined the Kohn-Sham electronic band structures, along the closed path Γ-M-K-Γ, using density functional theory. We have also determined the energies of the SSFs with respect to the perfect crystal finding that the (35) and (44) SSFs have unexpectedly low formation energies, for this reason we could expect these two defects to be easily generated/expanded either during the growth or post-growth process steps.

Systematic first principles calculations of the effects of stacking faults defects on the 4H-SiC band structure

AbstractShockley-type Stacking faults (SSF) in hexagonal Silicon Carbide polytypes have received considerable attention in recent years since it has been found that these defects are responsible for the degradation of forward I-V characteristics in p-i-n diodes. In order to extend the knowledge on these kind of defects and theoretically support experimental findings (specifically, photoluminescence spectral analysis), we have determined the Kohn-Sham electronic band structures, along the closed path Γ-M-K-Γ, using density functional theory. We have also determined the energies of the SSFs with respect to the perfect crystal finding that the (35) and (44) SSFs have unexpectedly low formation energies, for this reason we could expect these two defects to be easily generated/expanded either during the growth or post-growth process steps.

Photoluminescence Properties and 5D0 Decay Analysis of LaF3:Eu3+ Nanocrystals Prepared by Using Surfactant Assist

A cationic surfactant, cetyltrimethylammonium bromide, was used to prepare LaF3:Eu3+ nanocrystals via a hydrothermal route. The influences of post-annealing temperature on the size and morphology as well as on the photoluminescence (PL) properties were studied. It was found that the PL intensity was maximized when LaF3:Eu3+ nanocrystals were calcined at 600°C. By applying a time-resolved PL spectral analysis to the 5D0–7F1, 2 decay curves, we could conclude that at the annealing temperature the most of Eu3+ ions (94.6%) were successfully incorporated in a higher symmetric site in a LaF3 lattice structure and as a result engaged in the strong PL.

Biological Synthesis of Size-Controlled Cadmium Sulfide Nanoparticles Using ImmobilizedRhodobacter sphaeroides

Size-controlled cadmium sulfide nanoparticles were successfully synthesized by immobilizedRhodobacter sphaeroidesin the study. The dynamic process that Cd2+was transported from solution into cell by livingR. sphaeroideswas characterized by transmission electron microscopy (TEM). Culture time, as an important physiological parameter forR. sphaeroidesgrowth, could significantly control the size of cadmium sulfide nanoparticles. TEM demonstrated that the average sizes of spherical cadmium sulfide nanoparticles were 2.3 ± 0.15, 6.8 ± 0.22, and 36.8 ± 0.25 nm at culture times of 36, 42, and 48 h, respectively. Also, the UV–vis and photoluminescence spectral analysis of cadmium sulfide nanoparticles were performed.

Systematic Tuning of the Luminescent Properties of Self-Activated ZnGa2O4 Phosphors by Cd Ion Substitution

The effect of host compositions on the luminescent properties of spinel-type ZnGa2O4 phosphors was investigated by systematic substitution of Cd2+ for Zn2+ in the host lattice. A continuous solid solution with the composition (Zn1−xCdx)Ga2O4 (0≤x≤1.0) was synthesized at 950°C as self-activated phosphors, as indicated by X-ray diffraction (XRD) analysis. With increasing substitution of Cd2+ the emission and excitation wavelengths (λem and λexc) of self-activated (Zn1−xCdx)Ga2O4 were observed to exhibit a red shift, as indicated by photoluminescence spectral analysis. Similar results were also confirmed by cathodoluminescence data. Our observations are attributed to the systematic narrowing of the energy gap of the host attributed to expanding lattice dimensions induced by Cd2+ substitution. A CIE chromaticity diagram manifests the effect of Cd2+ doping on variation of hue for the (Zn1−xCdx)Ga2O4 gallate phosphors.