جستجوی مقالات مرتبط با کلیدواژه « photoluminescence » در نشریات گروه « فنی و مهندسی »

Recently, plasmonic nanoparticles with unique optical properties have been used in nanomedicine ranging from optical biosensing to bioimaging to drug delivery. Meanwhile, gold nanoparticles with very small and uniform size are desirable for these applications due to their low toxicity. In this project, reduction of gold by sodium borohydride (NaBH4) led to preparation of metal nanoparticles anchored gelatin matrix successfully. Due to its high biocompatibility, gelatin is very suitable as a stabilizing agent and despite other organic capping agents, it reduces the toxicity of these Au nanoparticles (Au Nps). These nanomaterials have been studied using Fourier transformed infrared (FT-IR), Optical Absorption, Photoluminescence (PL) spectroscopy techniques, using transmission electron microscope (TEM) and X ray diffraction (XRD). And influence of different concentrations of reducing agent have been investigated in preparation and optical properties of Au Nanoparticles with Gelatin as a capping agent. These nanomaterials are very promising for making devices with high luminosity in nano dimensions. In addition, since non -toxic and solvent materials are used in synthesis, the integration of these particles into a variety of systems, especially those related to biological and biomedical applications, can be practical and useful.

Stable photoluminescence is a phenomenon that is excited by irradiating high-energy light (usually ultraviolet light and sometimes beta rays) to a given substance. After the excitation stops, visible light is emitted from the excited electron states. The material will be done for a time that can be evaluated from seconds to several hours.In the present research, in the first stage, the synthesis of SrAl2O4 with stoichiometric percentages was investigated by solid-state reaction method at temperatures of 900, 1100, 1300, and 1500 ℃. Then, Dy2O3 and Y2O3 additives were added to the SrAl2O4 mixture with ratios of 1 to 4% by weight. The crystal structure and network of the SrAl2O4 host were determined by X-ray diffraction (XRD) analysis. The emission intensity of the mentioned factors was investigated by photoluminescence spectrophotometry (PL) with radiation at the wavelength of 237 nm, and the emission obtained in the wavelength range of 500-540 nm in the sample with different additives. Also, Fourier Transform Infrared Spectroscopy (FTIR) of the host composition and optimized samples with additives were also performed. The microstructure of the synthesized particles was examined using a scanning electron microscope (SEM).

Graphene quantum dots (GQDs) are considered a new member of the carbon family</em> </em>and shine amongst other members thanks to their superior electrochemical, optical, and structural</em> </em>properties. Graphene quantum dots are zero-dimensional nanostructures of less than 100 nm graphene sheets and contain one or more graphene layers. One of the essential features of these materials is the presence of graphene structure, which brings high crystallinity with a multiple carbon structure of SP2</sup> type. The characteristics of adjustable luminescence, electrical conductivity, and high specific surface area are all quantum confinement and edge effects. These properties make graphene quantum dots important in various applications such as medicine, catalyst, solar cell, and supercapacitor. This article reviews graphene quantum dots' properties, structure, synthesis methods, and applications. 

In this research, Un-doped zinc sulfide and copper doped thin films in concentrations of 3%, 4% and 7% were deposited on glass substrate by thermal evaporation method, followed by measuring and analyzing linear and non-linear optical properties of the prepared samples using Ultraviolet Visible spectrophotometry (UV-Vis), Photoluminescence (PL) and Z-scan device. The structural properties of the sample and quantitative analysis of data were examined using X-ray diffraction (XRD). Peaks resulted from charts showed that impurities in thin films of zinc sulfide did not led to a new phase in the samples, but relative intensity of peaks increased. Using measured data of the absorption spectrum, the absorption values and the nano-structured band gap of zinc sulfide and doped zinc sulfide with copper were calculated. The photoluminescence illustrated that with increasing concentrations of copper ions, PL intensity decreased. Non-linear optical measurements using continuous wave laser with wavelength of 532 nm for open and closed aperture showed that nonlinear absorption coefficient was positive for the zinc sulfide film and negative for zinc sulfide thin films with copper doped zinc. Furthermore, the refractive index and nonlinear absorption increase with increasing concentration.

In this research, doped and undoped BaMgAl10O17 nanoparticles were synthsized using a new simple combustion synthetic method. A hybrid fuel consisting of urea and glycine was utilized in absence of reductive atmosphe .The morphology, structure, purity of sample phases and the features of nanoparticles light-glowing were investigared using field emission scanning electron microscope (FE-SEM), X-Ray Diffraction (XRD) pattern, and Photoluminescence (PL). The effect of urea fuel was studied either solely or mixed with glycine for the dopant reduction. The results of morphology and X-ray diffraction imply narrow-bar-structured rice with an approximated dimension of 45 - 65 nm with roughly high purity. In the synthesized doped europium with urea hybrid fuel and glycine, the photoluminescence emission spectrum is observed within the wavelengthrange of 400-500 nm centered at 447 nm. The scintillation responses of the samples to the 90Sr beta and 241Am gamma radiation sources and the ,discrimination capability of beta and gamma emissions in the 90Sr/90Y sources are investigated. The results showed that the activated nanoparticles having doped Eu2+ have a good sensitivity to bate particles and. can be an appropriated alternative for detection applications of beta particles in the spaces combined with gamma photons and beta particles.

Zinc oxide (ZnO) is used widely in electrical and optical applications due to its wide band gap and also semiconductor properties. In the present study ZnO and Al doped (Al/Zn ratio equals to 6 wt.%) nanofibers (NFs) were synthesized by electrospinning method and post calcination at different temperatures 250, 300 and 400 ˚C. The effect of dopant on  microstructure, crystallography, functional molecule groups, and photoluminescence behavior of ZnO NFs were studied by means of scanning electron microscopy (SEM), X-ray diffraction pattern (XRD), Fourier-transform infrared spectroscopy (FTIR), and photoluminescence spectroscopy (PL), respectively. Results showed that the average diameter of ZnO NFs was increased from 131 to 468 nm after calcination. XRD analysis indicated that the hexagonal wurtzite ZnO was formed in both samples. Also it confirmed that the Al dopant was incorporated into ZnO NFs. Comparison of FTIR spectra showed that the Al doping caused to shift the Zn-O band to higher frequencies and also construct the stronger bonds inside the ZnO lattice. PL results also revealed that the Al doping enhanced the optical properties. It is because that the point defects issued by Al doping create lower energy levels for transferring the electrons from conduction band to valence band.

In the present work CdTe/ ZnS, ZnSe, CdS, CdSe core-shell quantum dots were synthesized via co-precipitation route. The effect of reflux intervals from 1 to 7 hours, on the CdTe cores, characteristics such as: photoluminescence properties, band gap, structure, and microstructure were studied. Results showed that synthesis with the reflux time of 1 hour led to proper CdTe core with the size of about 4nm, emission wavelength of 555 nm, and band gap of 2.25 eV. More reflux time caused to particle size enlargement, emission shift to higher wavelength values, and band gap decrease. Moreover, ZnS, ZnSe, CdS, and CdSe shells were in-situ synthesized on the CdTe cores. Formation of these shells led to emission red shift with the wavelength up to 591 nm and band gap decrease to 2.15 eV.

In this study, nanoporous anodic aluminium oxide (NAAO) layers were synthesized by mild and mild-hard anodization two methods in a solution of oxalic acid and NAAO-Sm3 nanocomposite were synthesized by boiling the (NAAO) layers in a solution of samarium nitrate. Then, the samples were annealed at different temperatures under argon atmosphere. For characterization of the morphology, phase structure, energy levels, and emission wavelengths of the NAAO-Sm3 nanocomposite layers from a field emission scanning electron microscope (FE-SEM), x-ray diffraction (XRD), and photoluminescence (PL) spectroscopy were respectively used. The results indicate that increasing annealing temperature leads to decreasing the PL spectra intensity at wavelengths of 397 and 433 nm that related to (oxygen vacancies) but the PL intensity of the NAAO-Sm3 nanocomposite layer is increased at 400 nm wavelength. With the excitation of the NAAO-Sm3 nanocomposite layer at 400 nm wavelength, four main emission bands of the 4F-4F intra-configuration transitions of ions Sm3 were clearly observed. These transitions include 4G5/2 → 6H5/2 (556 nm, green) and 4G5 2 → 6H7/2 (601nm, orange), 4G5/2 → 6H9/2 (647 nm, reddish), and 4G5/2→ 6H11/2 (709nm, red), respectively

In this study, CaWO4 and CaWO4:Ba2+ were synthesized by precipitation method with using of CaCl2, Na2WO4 AND BaCl2 as raw materials. synthesized powders were characterized by X-Ray diffraction (XRD), scaning microscope (SEM) photoluminescence tests. The results showed that after calcination at 500C /3hr, crystallization of CaWO4 were improved and amount of flourescence emision of CaWO4 were decreased and shifted and band gap energy increased.

The ZnO quantum dots (QDs) were successfully synthesized via co-precipitation technique and the effect of Mn2+ ions concentration as dopant on the optical properties was studied. To control the particle size by limiting the growth of the particles after the nucleation and to provide a side group on surface which can be further conjugated to bio-cell using polyethylene glycol (PEG) as bio-compatible capping agent. XRD analyses revealed single phase ZnO wurtzite crystal structure. TEM micrograph illustrates that the final QDs were about 10-30 nm in diameter with spherical shape. Also, the organic groups on the surface of nano-particles (NPs) were characterized by Fourier transform infrared spectroscopy (FTIR). From photoluminescence spectra, besides emission peak at 356 nm related to ZnO, doping Mn2+ ions in the host lattice led to appearance of the new visible emission band in the range of 410-450 nm because of 4T1→6A1 transition. Results show that the final QDs have potential for biochemical optical sensing.