Ograniczanie wyników
Czasopisma help
Autorzy help
Lata help
Preferencje help
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 113

Liczba wyników na stronie
first rewind previous Strona / 6 next fast forward last
Wyniki wyszukiwania
Wyszukiwano:
w słowach kluczowych:  photoluminescence
help Sortuj według:

help Ogranicz wyniki do:
first rewind previous Strona / 6 next fast forward last
EN
We present comprehensive investigation of the optical properties of hybrid-barrier GaSb-based resonant tunneling structures, containing a bulk-like GaInAsSb absorption layer and two asymmetric type II GaSb/InAs/AlSb quantum wells. Methods of optical spectroscopy by means of Fourier-transformed photoluminescence and photoreflectance are employed to probe optical transitions in this complex multilayer system. Based on the comparison between the absorption-like and emission-like spectra (also in function of temperature) confronted with band structure calculations four main transitions could be resolved and identified. For one of them, there has been observed unusually strong linear polarization dependence never reported in structures of that kind. It has been interpreted as related to a transition at the GaSb/GaInAsSb interface, for which various scenarios causing the polarization selectivity are discussed.
EN
ZnO thin layers were deposited on p-type silicon substrates by the sol-gel spin-coating method and, then, annealed at various temperatures in the range of 573-873 K. Photoluminescence was carried out in the temperature range of 20-300 K. All samples showed two dominant peaks that have UV emissions from 300 nm to 400 nm and visible emissions from 400 nm to 800 nm. Influence of temperature on morphology and chemical composition of fabricated thin layers was examined by XRD, SEM, FTIR, and Raman spectroscopy. These measurements indicate that ZnO structure is obtained for samples annealed at temperatures above 573 K. It means that below this temperature, the obtained thin films are not pure zinc oxide. Thus, annealing temperature significantly affected crystallinity of the thin films.
EN
In the presented work, the influence of the quantum well and barrier thicknesses on optical characteristics of InGaAs/AlInAs superlattices was reported. Six different structures of In0.53Ga0.47As/Al0.48In0.52As superlattices lattice-matched to InP were grown by low pressure metal organic vapour phase epitaxy (LP-MOVPE). Optical properties of the obtained structures were examined by means of photoluminescence spectroscopy. This technique allows quick, simple and non-destructive measurements of radiative optical transitions in different semiconductor heterostructures.The analysis of recorded photoluminescence spectra revealed the influence of the quantum well and barrier thicknesses on the emission line energy.
EN
In the presented work, an optical approach of stress determining in metalorganic vapor phase epitaxy (MOVPE) grown quantum cascade laser (QCL) structures was reported. In the case of such sophisticated structures containing hundreds of thin layers, it is important to minimize the stress generated in the QCL core. Techniques enabling determination of stress in such thin layers as those described in the article are photoluminescence and Raman spectroscopies. Based on Raman shift or changes in photoluminescence signal, it is possible to analyze stress occurring in the structure.
5
Content available remote Study of Ho doped Ag2S thin films prepared by CBD method
EN
Ho doped Ag2S thin films were grown on the glass substrate by chemical bath deposition (CBD) method at room temperature. The bath contained aqueous solution of silver nitrate, thiourea, EDTA, ammonia and holmium nitrate. Silver nitrate was used as a silver (Ag+) ion source; thiourea as sulfur (S−) ion source, EDTA was a complexing agent while ammonia was used to maintain pH, Ho(NO3)3 was taken as a source of Ho ions. The optical absorption edge of undoped (pure) and Ho doped silver sulfide films was determined between 324 nm and 298 nm showing blue shift as compared to bulk Ag2S. Band gaps calculated from Tauc plot also showed an increase in values for doped samples. The increase in band gap indicates reduced particle size in the prepared Ho doped films. The photoluminescence emission peaks were observed at around 578 nm to 601 nm wavelength and excitation peaks were found at 351 nm to 294 nm for undoped and doped films. The SEM micrograph consists of globular ball type and flower type structures observed in the prepared films of Ho doped Ag2S.
EN
Novel nonlinear optical semi-organic, potassium phthalate di lithium borate (KPDLiB) single crystals were successfully grown by the slow solvent evaporation technique. Good crystalline nature and an orthorhombic structure were confirmed by powder X-ray diffraction and single crystal X-ray diffraction studies. The functional groups of KPDLiB were identified using FT-IR spectrum recorded in the range of 4000 cm-1 to 450 cm-1. UV-Vis spectrum showed transmitting ability of the crystals in the entire visible region. The photoluminescence spectrum exhibited good fluorescence emission in a visible region at 384 nm, 416 nm and 578 nm. The second harmonic generation efficiency of the grown crystal was evaluated from Kurtz powder technique.
EN
We have investigated the spectroscopic properties of Er3+-doped fluorotellurite glasses with the basic molar composition 75%TeO2–10%P2O5–10%ZnO–5%PbF2, modified by replacing 5% TeO2 by a metal oxide, namely WO3 or Nb2O5. The absorption edge of the glasses studied has been described within the Urbach approach, while the absorption and photoluminescence spectra have been analyzed in terms of the standard Judd–Ofelt theory, along with the photoluminescence decay of the 4I13/2 and 4S3/2 levels of the Er3+ ion. The absorption and emission spectra of the 4I15/2↔ 4I13/2infrared transition have been analyzed within the McCumber theory to yield the peak emission cross-section and figure of merit for the amplifier gain. It appears that the fluorotellurite glass containing WO3 as a modifier is characterized by the largest figure of merit, indicating this matrix as a promising new host for doping with Er3+ ions.
EN
Sensitivity of dyes on the base of 4-valence tin complexes to the composition of environment was researched. It has been found out that such dyes by themselves keep stability and inactivity to the composition of atmosphere. However, the photoluminescence properties of the nanostructures on their base can differ sufficiently depending on conditions of their formation. So the glow intensity of the nanoparticle ensembles of dyes having amine substitute in the hydrazonic fragment depends on the concentration of solution which was used during their formation. Optimal concentration exists and its excess leads to weak luminescence due to concentration quenching. Thus, if the nanoparticle ensemble, which was formed at the optimal concentration will be placed into ammonium atmosphere, it will be equivalent to formation of this ensemble by inflated concentration of the saturated solution. So photoluminescence of such system will be weak. Thereby reduced glow intensity will keep sufficiently long time due to the appearance of leakage channels in the form of bridge bonds. In such manner one can register the presence of ammonium in the environment. Initial intensity of luminescence may be re-established by removing extraneous gas with the aid of the short-time low-temperature anneal. In addition, the ligand in the coordination set of the dye plays a part of an interstitial impurity, so its presence leads to certain distribution of the charges in the system. It has been estimated experimentally that less intensive glow corresponds to the charge distribution in the system with the one-dentant ligand, namely by higher content of chlorine ions than in the case of bi-dentant one. This difference is more evident for dyes having hydroxyl substitute in the hydrazonic fragment. Thus, if the nanoparticle ensemble of such dye having a bi-dentant ligand will be placed into the atmosphere containing hydrogen chloride vapours, it changes the charge distribution to the typical one for the dye having one-dentant ligand artificially. It also will lead to weakening of the glow of the system. Initial intensity of luminescence may be re-established by removing the extraneous gas again with the aid of the anneal by the same conditions. The usage of specified properties makes it possible to construct reliable and responsive detectors of ammonium or hydrogen chloride vapours by the change of the detecting element in the known luminescence gas sensors to the nanoparticle ensemble of an appropriate dye.
9
Content available remote Structural and optical properties of Dy3+ doped Sr2SiO4 phosphors
EN
Dysprosium doped strontium silicate phosphor namely (Sr2SiO4:Dy3+) was prepared by low-temperature solution combustion method using urea (CO(NH2)2) as a fuel. The material was characterized by powder X-ray diffraction (XRD), FT-IR, SEM and EDX. The average crystallite sizes was calculated by Scherer formula. Thermoluminescence study was carried out for the phosphor which showed single glow curve. The kinetic parameter were calculated by using Chen’s glow curve method. Photoluminescence spectra revealed strong transition at 473 nm (blue), 571 nm (yellow) and weak transition at 645 nm (red). These peaks were assigned to transition 4F9/2 → 6H15/2, 13/2 , 11/2. CIE graph of Sr2SiO4:Dy3+phosphor is suitable for the generation of white light emission.
EN
In this paper, Cd0.3Zn0.7S thin film has been electrodeposited from aqueous bath containing CdSO4, ZnSO4, Na2S2O3 and EDTA, having pH ~ 14. The structural, optical, morphological, surface wettability and photoluminescence properties of the film were investigated. The XRD pattern showed that the film consisted of mixed phases of CdS and ZnS with polycrystalline structure. The bandgap of the film was evaluated as 2.69 eV. The AFM study revealed that the Cd0.3Zn0.7S thin film contained spherical grains with root mean square roughness of 6.09 nm. The water contact angle measurement showed that the thin film was hydrophilic in nature. Moreover, the PL study revealed that the excitation wavelength was 460 nm.
EN
Present paper reports optical and electrical properties of samarium doped CdSe nanocrystalline thin film which was grown on a glass substrate by chemical bath deposition method (CBD). X-ray diffraction (XRD) analysis revealed that the deposited films were nanocrystalline with sphalerite cubic structure. The average crystallite size calculated from FWHM of XRD peaks was found to be 10.11 nm. The bandgap of the Sm doped CdSe nanocrystalline thin films was calculated to be 1.91 eV to 2.22 eV. The optical absorption edge of undoped (pure) and Sm doped CdSe films was obtained between 650 nm to 640 nm showing blue shift as compared to bulk CdSe. Sm doping further enhanced the photoconductivity of these films. The I-V characteristic confirmed the suitability of prepared films for photosensor applications.
12
Content available remote CdO-Fe3O4 nanocomposite with enhanced magnetic and photocatalytic properties
EN
Pure CdO nanopowder and CdO-Fe3O4 nanocomposite were synthesized by a cost effective chemical method, and the samples were characterized by XRD, SEM, TEM, FT-IR, UV-Vis-NIR and PL. Also, magnetic and photocatalytic properties of the synthesized samples were studied. XRD patterns of the composite confirm the presence of diffraction peaks related to both CdO and Fe3O4. EDX spectrum confirms the presence of the elements Cd, O and Fe in the composite. Peaks related to Cd–O and Fe–O bonds were observed respectively at 688 cm−1 and 592 cm−1 in the FT-IR spectrum. The paramagnetic behavior of pure CdO becomes ferromagnetic when coupled with Fe3O4. The composite exhibited a high photodegradation efficiency of 92.85 % against the degradation of methylene blue dye under visible light radiation.
EN
In the present investigation optical, electro-optical and dielectric properties have been measured for nematic liquid crystal (NLC) material 1550C which is consisted of 4’-(trans, trans-4-alkylbicyclohexyl) carbonates and 4’-(4-(trans,trans-4-alkyl)-4-cyanobicyclohexane, dispersed with fluorescent dye (Benzo 2,1,3 Thiadiazole) in two different concentrations. Photoluminescence has been enhanced for dye dispersed system which is the key finding of this investigation. UV absorbance study has also been performed and found to be increased for composite system. Enhanced birefringence after dispersion of dye into pure NLC is also a prominent result of this investigation. Relative permittivity, threshold voltage and dielectric anisotropy have also been measured and found to be increased. The outcome of the present work may be very useful in the construction of liquid crystal displays (LCDs).
EN
Zr0.99Gd0.01O2, Zr0.98Gd0.01Dy0.01O2 and Zr0.99Gd0.01Yb0.1O2 phosphors were synthesized by Pechini method at 1200 °C for 12 h in air. The phosphors were characterized by using X-ray powder diffraction (XRD), differential thermal analysis/thermal gravimetry (DTA/TG), scanning electron microscopy (SEM) and photoluminescence spectrofluorometer (PL). X-ray powder diffraction studies showed that the phosphors were crystallized as monoclinic and tetragonal multiphases. The particle size of the phosphors after heat treatment at 1200 °C was found to be of 200 nm to 250 nm. Luminescence studies on these phosphors have been carried out on the emission and excitation, along with lifetime measurements. The results of emission analysis indicate that the phosphors are expected to find potential applications as new optical materials.
15
Content available remote Optical properties of Sr2SiO4:Eu2+, Dy3+ phosphors prepared by combustion method
EN
In the present paper, TL and PL study of Dy3+ doped Sr2SiO4:Eu2+ phosphor is reported. A polycrystalline sample of Sr2SiO4:Eu2+, Dy3+ was prepared by combustion method. The obtained phosphor was characterized by powder X-ray diffraction, scanning electron microscopy, UV-Vis spectroscopy, PL and thermoluminescence. The results of the XRD studies obtained for Sr2SiO4:Eu2+, Dy3+ phosphor revealed its monoclinic structure. The average crystallite size was calculated as 12.77 nm. Thermoluminescence study was carried out for the phosphor using UV irradiation and a single glow peak was found. The thermoluminescence glow curves of the samples were measured at various concentrations of co-dopant. The kinetic parameter has been calculated using Chen’s glow curve method. In this paper, the photoluminescence and afterglow behaviour of these phosphors are reported.
EN
In this report, ternary semiconducting NixBi2−xS3(x = 0.2 M and 0.5 M) thin films were synthesized in situ for the first time by a chemical bath deposition technique at different bath temperatures (60 °C, 70 °C and 80 °C). The effects of concentration and deposition temperature on the deposited films were studied by combining the results of structural, morphological, optical and electrical analyses. The growth of NixBi2−xS3 films with good crystalline nature and interconnected grain arrangement takes place due to increasing the concentration of Ni2+ ions in bismuth sulfide matrix. EDS result confirmed the stoichiometry of NixBi2−xS3 formation. Wettability test demonstrated that the surface of the film was hydrophilic in nature. The optical absorption spectra revealed that the bandgap Eg of the x = 0.5 M film deposited at 70 °C was about 1.36 eV. Current-voltage (I-V) characteristics of the x = 0.5 M film deposited at 70 °C were studied under X-ray radiation and dark condition. An X-ray detection sensitivity analysis showed that the detection sensitivity is optimum when the bias voltage applied across the film is low (~0.9 V). These findings reveal that the film with x = 0.5 M deposited at 70 °C can be used as an efficient low cost X-ray sensor.
EN
The possibility of obtaining zinc selenide and zinc sulfide layers of hexagonal modification by isovalent substitution method is shown. They are characterized by intensive luminescence which is formed by the dominant annihilation of bound excitons for α-ZnSe and recombination on donor-acceptor pairs for α-ZnS. The resulting radiation covers the violet wavelength range. Quantum radiation efficiency reaches η = 10–12% for α-ZnSe and η = 5–8% for α-ZnS. The radiation is characterized by high temperature stability and repeatability of characteristics and parameters.
PL
Pokazano, że możliwe jest uzyskanie heterogennych warstw selenku i siarczku cynku o modyfikacji heksagonalnej za pomocą metody izowalentnego podstawienia. Charakteryzują się one intensywną luminescencją, która powstaje w wyniku anihilacji związanych ekscytonów dla dominującego pasma α-ZnSe i rekombinacji na parach donor-akceptor w przypadku α-ZnS. Otrzymane promieniowanie pokrywa fioletowy zakres optyczny. Sprawność kwantowa promieniowania wynosi η = 10–12% dla α-ZnSe i η = 5–8% dla α-ZnS. Promieniowanie charakteryzuje się wysoką stabilnością temperaturową oraz powtarzalnością charakterystyk i parametrów.
EN
Optically transparent single crystals of 2-amino-5-chloropyridinium-4-amino benzoate (2A5CP4AB) were grown at room temperature using solution growth technique. The structure was solved with a support of single crystal XRD, which revealed that the title compound belongs to the monoclinic crystal system having centrosymmetric space group P21/n. The UV-Vis spectrum and photoluminescence properties of the title compound showed the optical transmittance and emission behavior of the compound. The optical band gap was evaluated using the Tauc plot and it was found to be about 3.53 eV. The third order nonlinear optical behavior of the crystal was determined using Z-scan technique. Mechanical properties of the title compound were studied using Vickers microhardness study.
19
Content available remote Structural and luminescent properties of Fe3+ doped PVA capped CdTe nanoparticles
EN
During recent decades, magnetic and semiconductor nanoparticles have attracted significant attention of scientists in various fields of engineering, physics, chemistry, biology and medicine. Fe3+ doped PVA capped CdTe nanoparticles were prepared by co-precipitation method and characterized by powder X-ray diffraction, SEM, TEM, FT-IR, optical, EPR and PL techniques to collect the information about the crystal structure, coordination/local site symmetry of doped Fe3+ ions in the host lattice and the luminescent properties of prepared sample. Powder XRD data revealed that the crystal structure belongs to a cubic system and its lattice cell parameters were evaluated. The average crystallite size was estimated to be 8 nm. The morphology of prepared samples was analyzed by using SEM and TEM investigations. Functional groups of the prepared sample were observed in FT-IR spectra. Optical absorption and EPR studies have shown that on doping, Fe3+ ions enter the host lattice in octahedral site symmetry. PL studies of Fe3+ doped PVA capped CdTe nanoparticles revealed UV and blue emission bands. CIE chromaticity coordinates were also calculated from the emission spectrum of Fe3+ doped PVA capped CdTe nanoparticles.
EN
Undoped and Mn-doped thin ZnS films were deposited on ordinary glass substrates at temperature of 450 °C by an improved spray pyrolysis (ISP) method. The ISP parameters, such as carrier gas flow rate, solution flow rate and substrate temperature, were controlled with accuracy ±0.25 Lpm, ±1 mL/h and ±1 °C, respectively. A pulse-spray mode of the method was used to spray the precursor solution. Thin film samples were prepared for Mn-doping with the concentrations of 0 at.%, 1 at.%, 3 at.%, 6 at.%, 8 at.% and 12 at.% relative to Zn in the spray solution. The Mn-doping concentration dependent chemical composition, surface morphology, and structural, optical and photoluminescence (PL) properties were studied. All the thin films were well adherent, nearly stoichiometric, dense, uniform, and possessed cubic crystal structure with preferential orientation along h〈1 1 1〉 direction. A slight enhancement in structural properties, an increase in band gap, and a decrease in refractive index and dielectric constant with Mn-doping concentration were observed. The PL spectra of Mn-doped thin ZnS films at room temperature exhibited both the 490 nm blue defect-related emission and the 590 nm yellow-orange Mn2+ ion related emission. The observed yellow-orange emission intensity was maximum for 3 at.% of Mn-doping concentration in the spray solution.
first rewind previous Strona / 6 next fast forward last
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.