Search

Quantum dot (QD)-based single-photon emitter devices today are based on self-assembled random position nucleated QDs emitting at random wavelengths. Deterministic QD growth in position and emitter wavelength would be highly appreciated for industry-scale high-yield device manufacturing from wafers. Local droplet etching during molecular beam epitaxy is an all in situ method that allows excellent density control and predetermines the nucleation site of quantum dots. This method can produce strain-free GaAs QDs with excellent photonic and spin properties. Here, we focus on the emitter wavelength homogeneity. By wafer rotation-synchronized shutter opening time and adapted growth parameters, we grow QDs with a narrow peak emission wavelength homogeneity with no more than 1.2 nm shifts on a 45 mm diameter area and a narrow inhomogeneous ensemble broadening of only 2 nm at 4 K. The emission wavelength of these strain-free GaAs QDs is <800 nm, attractive for quantum optics experiments and quantum memory applications. We can use a similar random local droplet nucleation, nanohole drilling, and now, InAs infilling to produce QDs emitting in the telecommunication optical fiber transparency window around 1.3 µm, the so-called O-band. For this approach, we demonstrate good wavelength homogeneity and excellent density homogeneity beyond the possibilities of standard Stranski–Krastanov self-assembly. We discuss our methodology, structural and optical properties, and limitations set by our current setup capabilities. [ABSTRACT FROM AUTHOR]

We present a novel growth technique for fabricating low-density InAs/GaAs quantum dots that emit in the telecom O-band. This method combines local droplet etching on GaAs surfaces using gallium with Stranski–Krastanov growth initiated by InAs deposition. Quantum dots nucleate directly within nanoholes, avoiding the critical layer thickness typical of standard InAs Stranski–Krastanov growth, resulting in larger, low-density quantum dots. InGaAs strain reduction layers further redshift the emission into and beyond the telecom O-band. Photoluminescence spectra show a small energy difference between ground and excited states, while capacitance-voltage spectroscopy reveal small Coulomb blockade energy. Atomic force microscopy analysis indicates that quantum dots formed within nanoholes exhibit a larger volume compared to standard quantum dots. Additionally, these nanohole nucleated quantum dots require less indium to achieve O-band emission and demonstrate comparable or even better homogeneity, as indicated by the full-width at half-maximum. This improved homogeneity, low density, and increased size make these quantum dots particularly suitable for single-photon sources in quantum communication applications. [ABSTRACT FROM AUTHOR]

Atomically thin molybdenum disulfide (MoS2) is a two-dimensional semiconductor with versatile applications. The recent adoption of liquid molybdenum precursors in chemical vapor deposition has contributed significantly to the reproducible wafer-scale synthesis of MoS2 monolayer and few-layer films. In this work, we study the effects of the carrier gas flow rate on the properties of two-dimensional molybdenum disulfide grown by liquid-precursor-intermediate chemical vapor deposition on SiO2/Si substrates. We characterized the samples using Optical Microscopy, Scanning Electron Microscopy, Raman spectroscopy, and Photoluminescence spectroscopy. We analyzed samples grown with different nitrogen carrier flows, ranging from 150 to 300 sccm, and discussed the effect of carrier gas flows on their properties. We found a correlation between MoS2 flake lateral size, shape, and number of layers, and we present a qualitative growth model based on changes in sulfur provision caused by different carrier flows. We show how the use of liquid precursors can allow for the synthesis of homogeneous, single-layer flakes up to 100 µm in lateral size by optimizing the gas flow rate. These results are essential for gaining a deeper understanding of the growth process of MoS2. [ABSTRACT FROM AUTHOR]

Internal quantum efficiency (IQE) of AlGaN‐based multiple quantum wells (MQWs) on face‐to‐face‐annealed sputter‐deposited AlN templates is examined by photoluminescence spectroscopy. The excitation power density dependence of IQE is evaluated as a function of temperature under the selective excitation of the quantum wells. The temperature dependences of the maximum IQE and the corresponding excitation power density (EPD) are analyzed based on the rate equation models for carriers and excitons. The decrease of the maximum IQE and increase of the corresponding EPD are mainly due to the increase in the nonradiative recombination rate via nonradiative recombination centers. Furthermore, the nonradiative recombination rate for the MQW with an emission wavelength around 220 nm is activated at a lower temperature than the other samples, which is expected to lead to the lower IQE of the MQW with an emission wavelength around 220 nm. [ABSTRACT FROM AUTHOR]

Undoped and Cr doped β-Ga2O3 (100) single crystals are grown by optical floating zone method. The full width at half maximum of rocking curve is found to be 106 arc.sec for undoped β-Ga2O3 crystals whereas the 100 and 200 ppm of Cr doped β-Ga2O3 crystals display multiple rocking curves with large peak widths indicating the presence of structural defects. Raman measurements reveal broadening in the vibrational mode of ~ 350 cm− 1 with a shoulder peak indicating the Cr3+ dopants preferentially substitute for Ga3+ at the octahedral sites. Further, the Cr doped β-Ga2O3 crystals display strong optical absorption bands about 420 and 597 nm in the UV-Vis spectroscopy. Moreover, the observation of sharp characteristic photoluminescence emission lines at 690 and 697 nm also confirms the Cr substitution in the doped crystals. The indentation hardness increases nearly linear from 13.0 ± 0.6 to 17.9 ± 0.4 GPa whilst the indentation modulus decreases from 224.9 ± 21.4 to 202.4 ± 11.9 GPa upon Cr doping of 200 ppm in β-Ga2O3. The structural defects caused by the Cr doping interrupt the movement of indentation induced dislocations that results in the increase of hardness of the Cr doped β-Ga2O3 (100) single crystals. [ABSTRACT FROM AUTHOR]

This study used ultrasonication method to prepare graphitic carbon nitride (g-C3N4)/zirconium oxide (ZrO2) nanocomposites with varying ratios. Various approaches were used to characterize the as-prepared nanocomposites. The structural properties were investigated by x-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. XRD patterns showed that pure g-C3N4 has a unique peak, while ZrO2 has a monoclinic phase with no additional phases. The nanocomposites exhibited peaks from both materials, indicating the successful synthesis of the nanocomposites. The optical properties of the nanocomposites were studied using UV–Vis diffuse reflectance spectroscopy (DRS) and photoluminescence spectroscopy. According to Tauc's plot, the nanocomposites g-C3N4:ZrO2{1:0.5} (CZ1) and g-C3N4:ZrO2{1:2} (CZ2) showed bandgaps of 2.92 eV and 2.93 eV, respectively. The photoluminescence emission of the nanocomposites displayed a broad peak centered at ~ 450 nm. According to the CIE diagram, the nanocomposites exhibited strong emission in the blue region, with 80.4% purity. The average lifetime decay times of the nanocomposites were 0.18 ms and 0.01 ms. Based on these findings, it can be concluded that this material has the potential for use in the field of optoelectronics. [ABSTRACT FROM AUTHOR]

The detection of Pyrene, a toxic polycyclic aromatic hydrocarbon, is crucial for environmental monitoring due to its negative impacts on health and ecosystems. While photoluminescence (PL) spectroscopy holds promise for Pyrene detection, its current application is limited. This research aimed to address this gap by developing a novel PL spectroscopy method for Pyrene detection. The method utilizes a simple, low limit of detection (LOD), affordable, rapid, and user-friendly approach. A polyaniline-graphene quantum dot (PANI-GQD) nanocomposite film was synthesized as the sensing layer. For comparison, PL spectroscopy measurements were also taken using GQD and PANI alone. The fabricated thin films were thoroughly characterized using various techniques (FT-IR, UV–Vis, Raman, XRD, FE-SEM, EDX, TGA) to analyze their chemical, optical, physical, and structural properties. The developed PANI-GQD nanocomposite film-based PL spectroscopy successfully detected Pyrene concentrations ranging from 0.001 to 10 × 10–9 mol L−1. Notably, the method achieved an outstanding LOD of 0.40 × 10–9 mol L−1 (S/N = 5) for low-concentration Pyrene detection, surpassing previous limitations. This LOD is well within the WHO's set standards for Pyrene in aquatic environments (3.461 × 10–9 mol L−1). Overall, this research presents a valuable tool for detecting toxic materials relevant to environmental monitoring, with potential for significant socio-economic impact. [ABSTRACT FROM AUTHOR]

A model of the structure of thermally modified shungite carbon is proposed, which can be used as a container for the production and long-term retention of nanosized particles. Such nanoparticles are characterized by their inherent photoluminescence activity. Since nanosized carbon particles do not enter into chemical interaction with the shungite matrix under normal conditions, their luminescent properties are maintained for a long time. The description of the multilevel structure of shungite carbon by the model of randomly oriented agglomerations of turbostratic stacks of graphene sheets is confirmed by X-ray studies. [ABSTRACT FROM AUTHOR]

High-quality monolithic Ge-on-Si is sought for CMOS-compatible optoelectronic devices. We examine the structural characteristics of Ge-on-Si grown by the aspect ratio trapping (ART) method on a SiO2/Si(001) template in pre-patterned holes. Transmission electron microscopy and surface topography analysis revealed high-quality Ge islands overgrown from the ART holes in SiO2. The superior crystal quality of Ge ART growth was also confirmed by comparing x-ray diffraction (XRD) data of Ge ART and Ge planar epilayer samples. The XRD and micro-Raman data additionally show a small residual strain in the islands which vanishes by reducing the hole diameter from 280 nm to 180 nm, while leading to only a minor increase in the crystallographic inclinations of the Ge islands from 0.34 deg to 0.54 deg. With finite element method simulations, we find that the small residual strain in Ge originates during the cool-down from growth to room temperature because of thermal expansion coefficient mismatch between Ge and SiO2. A tensile force develops along the [001] axis of the Ge pillar whose faster shrinkage to the room temperature volume is restricted by the oversized surface island. [ABSTRACT FROM AUTHOR]

The paper investigates optical and spectral properties of ZnO nanoparticles dispersed p-(n-heptyloxy)benzoic acid (7-OBA) liquid crystalline (LC) compounds with the concentration of 1 to 2.5 wt.%. The prepared samples are characterized by various experimental techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible spectroscopy, differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and photoluminescence (PL) spectroscopy. The presence of ZnO nanoparticles is confirmed by the XRD. The crystallite size is found to be 68 nm. Phase transition temperatures and enthalpy values of pure and nanodispersed LC materials are measured by DSC. The texture of pure and nanodispersed LC phases like nematic and smectic, is observed through POM. Photoluminescence spectroscopy shows the dispersion of 2.5 wt.% ZnO nanoparticles in 7-OBA compound; the blue emission maximum shifts from 368 to 375 nm. The peak observed at 655 nm, is determined by point defects in the bandgap, namely vacancies and interstitial known as deep level emission. [ABSTRACT FROM AUTHOR]

Alloying small quantities of silver into Cu(In,Ga)Se2 is shown to improve the efficiency for wide and low bandgap solar cells. Low bandgap industrial Cu(In,Ga)(S,Se)2 absorbers are studied, substituting less than 10% of the copper with silver, using absolute photoluminescence and cathodoluminescence spectroscopy. Silver improves the grain size and promotes the interdiffusion of Ga and In across the depth of the absorber, resulting in a smoother bandgap gradient. However, a certain lateral inhomogeneity is observed near the front and back sides. The nonradiative losses in the bare absorbers are reduced by up to 30 meV. [ABSTRACT FROM AUTHOR]

ZnAl2O4 with a typical spinel structure is highly expected to be a novel rare‐earth‐free ion‐activated oxide phosphor with red emission, which holds high actual meaning for advancing phosphor‐converted light‐emitting diode (pc‐LED) lighting. Among the rare‐earth‐free activators, Mn4+ ions have emerged as one of the most promising activators. Considering the price advantage of MnCO3 generating Mn2+ ions and the charge compensation effect potentially obtaining Mn4+ ions from Mn2+ ions, this research delves into a collection of ZnAl2O4:Mn2+(Mn4+), x Li+ (x = 0%–40%) phosphors with Li+ as co‐dopant and MnCO3 as Mn2+ dopant source prepared by a high temperature solid‐state reaction method. The lattice structure was investigated using X‐ray diffraction (XRD), photoluminescence (PL), and photoluminescence excitation (PLE) spectroscopy. Results suggest a relatively high probability of Li+ ions occupying Zn2+ lattice sites. Furthermore, Li+ ion doping was assuredly found to facilitate the oxidization of Mn2+ to Mn4+, leading to a shift of luminescence peak from 516 to 656 nm. An intriguing phenomenon that the emission color changed with the Li+ doping content was also observed. Meanwhile, the luminescence intensity and quantum yield (QY) at different temperatures, as well as the relevant thermal quenching mechanism, were determined and elucidated detailedly. [ABSTRACT FROM AUTHOR]

A novel creation procedure for the nitrogen-vacancy (NV) center in diamond is investigated. After shallow nitrogen implantation, a continuous-wave laser is used to induce NV formation, while simultaneously exciting fluorescence to enable live observation. Our investigations imply that a different mechanism than heat induced vacancy diffusion causes the formation of NV centers with this method and we suggest possible alternative pathways which could be responsible, based on the observed properties. Furthermore, we test the procedure for its capabilities for the controlled creation of single centers and show that the emergence of individual centers can be tracked, while achieving sub-micrometer spatial precision.

GaAs‐AlGaAs based nanowire (NW) lasers hold great potential for on‐chip photonic applications, where lasing metrics have steadily improved over the years by optimizing resonator design and surface passivation methods. The factor that will ultimately limit the performance will depend on material properties, such as native‐ or impurity‐induced point defects and their impact on non‐radiative recombination. Here, the role of impurity‐induced point defects on the lasing performance of low‐threshold GaAs(Sb)‐AlGaAs NW‐lasers is evaluated, particularly by exploring Si‐dopants and their associated vacancy complexes. Si‐induced point defects and their self‐compensating nature are identified using correlated atom probe tomography, resonant Raman scattering, and photoluminescence experiments. Under pulsed optical excitation the lasing threshold is remarkably low (<10 µJ cm−2) and insensitive to impurity defects over a wide range of Si doping densities, while excess doping ([Si]>1019 cm−3) imposes increased threshold at low temperature. These characteristics coincide with increased Shockley‐Read‐Hall recombination, reflected by shorter carrier lifetimes, and reduced internal quantum efficiencies (IQE). Remarkably, despite the lower IQE the presence of self‐compensating Si‐vacancy defects provides an improved temperature stability in lasing threshold with higher characteristic temperature and room‐temperature lasing. These findings highlight an overall large tolerance of lasing metrics to impurity defects in GaAs‐AlGaAs based NW‐lasers. [ABSTRACT FROM AUTHOR]

Olive oil serves as a significant source of income for Palestinian farmers, both on a national and international scale. This study focuses on assessing the quality and identifying key compounds in olive oils from different regions, employing UV–visible absorption and photoluminescence spectroscopy. UV-visible absorbance analysis uncovered specific absorption bands associated with chlorophyll, and carotenoids. Additional measurements at 232, 266, 270, and 274 nm, along with K values calculations, indicated that the oils from these regions are predominantly extra virgin. Photoluminescence measurements in two and three dimensions revealed three distinct emission bands. The first, peaking at 320 nm, was linked to polyphenols, the second, a red emission at 670 nm, to chlorophyll, and the third, spanning 400–580 nm, to oxidation products and vitamin E. When examining olive oil adulteration with sunflower oil, both absorption and photoluminescence data exhibited a significant reduction in peak intensity for chlorophyll, carotenoids, and polyphenols. Additionally, this research explored pigment content in olives from various geographic origins, finding that the ratio values align with ideal standards for Extra Virgin Olive Oil (EVOO) and provided insights into the percentage of lutein within the carotenoid composition.

We present a novel growth technique for fabricating low-density InAs/GaAs quantum dots that emit in the telecom O-band. This method combines local droplet etching on GaAs surfaces using gallium with Stranski–Krastanov growth initiated by InAs deposition. Quantum dots nucleate directly within nanoholes, avoiding the critical layer thickness typical of standard InAs Stranski–Krastanov growth, resulting in larger, low-density quantum dots. InGaAs strain reduction layers further redshift the emission into and beyond the telecom O-band. Photoluminescence spectra show a small energy difference between ground and excited states, while capacitance-voltage spectroscopy reveal small Coulomb blockade energy. Atomic force microscopy analysis indicates that quantum dots formed within nanoholes exhibit a larger volume compared to standard quantum dots. Additionally, these nanohole nucleated quantum dots require less indium to achieve O-band emission and demonstrate comparable or even better homogeneity, as indicated by the full-width at half-maximum. This improved homogeneity, low density, and increased size make these quantum dots particularly suitable for single-photon sources in quantum communication applications.

Techniques for effectively harnessing lead (Pb) deposits for optimum utilization have attracted a lot of research interest. Results obtained from investigating the elemental composition, vibrational modes, and structural properties of a fired Pb composite deposit, which is purified using an electric kiln furnace and further annealed in palladium‐diffused hydrogen ambient, are reported in the present study. Both atomic force microscopy and scanning electron microscopy analysis on the deposit indicate that the Pb composite is composed of crystal‐like morphology. The vibrational modes obtained from the material are identical to the Raman spectrum reported for PbSO4. Also, data acquired from the energy‐dispersive X‐ray analysis of the annealed Pb composite material confirm the presence of zinc, carbon, silicon, sulfur, and oxygen in the material. At the same time, Pb appears to be the primary constituent with reference to its weight percentage composition compared to other elements. The findings from the present study may be vital for providing an improved understanding of the electronic and structural properties of the annealed Pb composite deposit while promoting the development of a feasible approach for the recovery and recycling of Pb for future related applications. [ABSTRACT FROM AUTHOR]

The time dynamics of luminescence intensity in the spectral maximum from the Nafion polymer membrane surface is studied. Luminescence was excited by a continuous wave diode laser with wavelength λ = 369 nm. The polymer membrane swelled in deionized water with a deuterium content of 157 ppm, as well as in deuterium-depleted water (deuterium content of 3 ppm). In photoluminescence spectroscopy experiments, a polymer Nafion membrane is irradiated with a radiofrequency electromagnetic wave at a frequency of 3 MHz. Submicrometer particles of colloidal gold are added to liquid samples. It turns out that when such particles added to deionized water and irradiated with radio frequency waves cause stochastic jumps in the luminescence intensity. This effect is absent as submicrometer gold particles are added to deuterium-depleted water. A qualitative model is proposed that relates luminescence intensity jumps to the effects of radio frequency radiation absorption on metal submicrometer particles and the emergence of a convection countercurrent near the membrane due to Rayleigh instability. [ABSTRACT FROM AUTHOR]

This research describes a simple and straightforward combustion synthesis for SrY2O4:Dy3+ nanoparticles. The synthesis of SrY2O4:Dy3+ was carried out with the use of urea as a fuel. Characterization techniques including as X-ray diffraction (XRD), transmission electron microscope (TEM), and scanning electron microscopy were used to investigate the effect of the synthesis procedure on the structural behaviour of the phosphor. The existence of orthorhombic structure is indicated by XRD. X-ray widening, Williamson–Hall (W–H) analysis, and a size–strain plot were used to examine the effect of crystallite sizes and lattice strain on the peak broadening of SrY2O4:Dy3+. Uniform deformation model (UDM), uniform stress deformation model (USDM), and uniform deformation energy density model (UDEDM), as well as the size–strain plot method, were used to determine strain, stress, and energy density parameters for all XRD peaks (SSP). W–H analysis, SSP, and TEM results all agreed on the mean particle sizes. To quantify visual properties, a photoluminescence spectroscopic method was implemented. Intense emission at 553 nm, characteristic of emission generated by the energy level transition of the Dy3+ ion, was detected in the emission spectra. [ABSTRACT FROM AUTHOR]

SnO2 and FeTiO3 nanocrystals and type-II heterojunctions with differing weight-ratios (SnO2–FeTiO3: 90–10, 92–8, and 95–5%) were synthesized, and the best photocatalyst was decorated with metallic Ag0. XRD showed that SnO2 and FeTiO3 have rutile and perovskite crystal structures respectively, whereas the small amounts of Ag0 was undetectable, after the junction, these structures were maintained with an impact on the crystal properties. PL-spectroscopy indicated that the increased FeTiO3 and Ag0 weight-ratios diminished the PL-emission, prolonging the lifetime of photogenerated charge carriers. SEM proved a good mixing of FeTiO3 and SnO2 nanocrystals, and EDX proved the formation of the heterojunctions. The adsorption kinetic curves obey to the pseudo-first-order-model, according to Weber and Boyd models, film-diffusion and/or chemical reaction predominate initially, followed by the pore-diffusion process. The materials' photocatalytic performances were tested under visible-light irradiation, finding FeTiO3–SnO2(92–8%)–Ag4% the best photocatalyst. Finally, a mechanism of charges transfers within the material explaining the photocatalysis was proposed. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) is one of the commonly used methods to determine the energy gap ( E g ) of semiconductors. In order to use it correctly, however, the shape of the PL peak must be properly analyzed; otherwise, the value of E g is burdened with a large error. E g is often mistakenly attributed to the PL peak position, which in type-II superlattices (T2SLs) exhibits typical "S-shaped" behavior as a function of temperature, significantly different from the Varshni model used to define the energy gap of III-V compounds. The position peak of the PL relative to the real E g in T2SLs is red-shifted because of the carrier localization at low temperatures and blue-shifted because of the free carrier emission at high temperatures. To correctly determine E g , the shape of the PL peak should be analyzed using the theoretical PL line shape model that takes into account both localized (below the bandgap) and free carriers (above the bandgap) emissions. This work shows that the use of such a model to analyze the shape of the PL signal gives the correct results of determining E g for mid-wave infrared InAs/InAsSb T2SL, which showed a significant contribution of localized states in optical transitions and characteristic "S-shaped" PL peak behavior. This allowed us to determine the correct values of the Varshni coefficients for a given T2SL. The result also agrees with the theoretical calculations of E g made using the k·p method. [ABSTRACT FROM AUTHOR]

The purpose of the presented study is to examine the impact of zinc oxide nanoparticles (ZnO NPs) on the spectrum features of poly [2-methoxy-5-(3′,7′-dimethyloctyloxy)-1, 4-phenylenevinylene] (MDMO-PPV). The characteristics of the MDMO-PPV and doped ZnO NPS samples were assessed using several techniques. A set of solutions of MDMO-PPV in toluene that were doped with different ratio percentages of ZnO NPs was prepared to obtain thin films. Pristine and composite solutions were spin-coated on glass substrates. It was observed that MDMO-PPV had two distinct absorbance bands at 310 and 500   nm in its absorption spectrum. The UV-Vis spectrum was dramatically changed when 5 % of ZnO NPs were added. The result showed a significant reduction in absorption of the band 500   nm , while 310   nm absorption increased rapidly and became more pronounced. Upon adding (10%) ZnONPs to the sample, no noticeable change was observed in the 500 nm band. However, the 310 nm band shifted towards the blue region. There is a dominant peak in the PL spectrum of MDMO-PPV in its pristine form around 575   nm and a smaller hump around 600   nm of the spectrum. The spectral profile at 600 nm and the intensity of both bands are improved by raising the ZnO NP concentration. These bands feature two vibronic transitions identified as (0-0) and (0-1). When the dopant concentration increased to the maximum dopant percentage ( 10 % ), the energy band gap values increased by 0.21   eV compared to the pristine MDMO-PPV. In addition, the refractive index (n) decreased to its lowest value of 2.30 with the presence of concentrations of ZnO NPs. [ABSTRACT FROM AUTHOR]

GaAs-based nanowires are among the most promising candidates for realizing a monolithic integration of III–V optoelectronics on the Si platform. To realize their full potential for applications as light absorbers and emitters, it is crucial to understand their interaction with light governing the absorption and extraction efficiency as well as the carrier recombination dynamics determining the radiative efficiency. Here, we study the spontaneous emission of zincblende GaAs/(Al,Ga)As core/shell nanowire arrays by μ-photoluminescence spectroscopy. These ordered arrays are synthesized on patterned Si(111) substrates using molecular beam epitaxy and exhibit an exceptionally low degree of polytypism for interwire separations exceeding a critical value. We record emission spectra over more than five orders of excitation density for both steady-state and pulsed excitation to identify the nature of the recombination channels. An abrupt Mott transition from excitonic to electron–hole plasma recombination is observed, and the corresponding Mott density is derived. Combining these experiments with simulations and additional direct measurements of the external quantum efficiency using a perfect diffuse reflector as a reference, we are able to extract the internal quantum efficiency as a function of carrier density and temperature, as well as the extraction efficiency of the nanowire array. The results vividly document the high potential of GaAs/(Al,Ga)As core/shell nanowires for efficient light emitters integrated on the Si platform. Furthermore, the methodology established in this work can be applied to nanowires of other materials systems of interest for optoelectronic applications. [ABSTRACT FROM AUTHOR]

We compared the photoluminescence (PL) properties of AlInAsSb digital alloy samples with different periods grown on GaSb (001) substrates by molecular beam epitaxy. Temperature-dependent S-shape behavior is observed and explained using a thermally activated redistribution model within a Gaussian distribution of localized states. There are two different mechanisms for the origin of the PL intensity quenching for the AlInAsSb digital alloy. The high-temperature activation energy E 1 is positively correlated with the interface thickness, whereas the low-temperature activation energy E 2 is negatively correlated with the interface thickness. A quantitative high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) study shows that the interface quality improves as the interface thickness increases. Our results confirm that E 1 comes from carrier trapping at a state in the InSb interface layer, while E 2 originates from the exciton binding energy due to the roughness of the AlAs interface layer. [ABSTRACT FROM AUTHOR]

Polymer blends have got considerable attention for their potential optoelectronic and photonic applications due to several advantages such as easy processing, low cost, flexibility, and good mechanical properties. This work reports the structure and optical properties of solution cast binary blends of poly (methyl methacrylate) (PMMA) and poly (vinyl carbazole) (PVK). Here, the position and/or intensity of characteristic FTIR peaks reveal the changes of the structure of PMMA on PVK content while the surface morphology changes from highly smooth for pure PMMA to flaky structured (PVK 5%) and then to agglomerated morphologies for these blends. A red shift in optical absorption edge and decrease in optical transmission with PVK content in PMMA based blends. The emission spectra exhibit intensity escalation by 340 times with respect to PMMA for PVK-15 blends and then decreases with further addition of PVK in these blends. These results are very important for the advent of new optoelectronic functionalities for these polymer blends. [ABSTRACT FROM AUTHOR]

The high solid state reaction technique is used to create Y2SiO5 that is doped with Eu3+. The technique is appropriate for mass production. The use of high temperature synthesis procedures can improve luminescence efficiency in several ways. Europium was used in samples at varying concentrations (0.5–1.5 mol%). Transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques were used to characterize the prepared sample. Scherer’s formula determined the particle size to be around 45 nm. The excitation and emission spectra of the photoluminescence with varied concentrations of europium are excellent. Broad peaks at 257 nm with a shoulder peak at 275 nm were discovered in the excitation spectra monitored at 617 nm. The emission spectra were observed at 257 nm and show all visible peaking, with the strongest peak being at 617 nm (red emission). Up to 0.5 mol%, the concentration of europium causes an increase in PL spectrum intensity before a reduction in intensity due to concentration quenching. The Commission Internationale de I’Eclairage (CIE) approach was used to determine the spectrophotometric determination. [ABSTRACT FROM AUTHOR]

Photoluminescence from the surface of Nafion polymer membrane upon swelling in water under irradiation by electromagnetic waves at a frequency of 100 MHz was studied. In these experiments, natural deionized (DI) water with a deuterium content of 157 ppm and deuterium-depleted water (DDW, deuterium content is 1 ppm) were explored. We have studied for the first time the effect of linearly and randomly polarized low-frequency electromagnetic radiation on the luminescence excitation. To obtain low-frequency electromagnetic radiation with random polarizations, anisotropic solid submicron-sized particles, which result in depolarization effects upon scattering of the initially linearly polarized radiation, were used. We compared two types of colloidal particles: spherically symmetric (isotropic) and elongated (anisotropic). If the radiation is linearly polarized, the intensity of luminescence from the Nafion surface decreases exponentially as the polymer is soaked, and such a behavior is observed both in natural DI water and DDW. When spherically symmetric submicron-sized particles are added to a liquid sample, the luminescence intensity also decreases exponentially upon swelling in both natural DI water and DDW. At the same time, when anisotropic submicron-sized particles are added to DI water, random jumps in the luminescence intensity appear during swelling. At the same time, the exponential decrease in the luminescence intensity is retained upon swelling in DDW. A qualitative theoretical model for the occurrence of random jumps in the luminescence intensity is presented. [ABSTRACT FROM AUTHOR]

The production of superlattices with pseudomorphically strained quantum wells (QWs) {InxGa1–xAs/GaAs} grown by molecular beam epitaxy on GaAs substrates with (100), (110), and (111)A crystallographic surface orientations is reported. The quality of the crystal structure of epitaxial samples is assessed using the atomic force microscopy of their surface. The manifestation of a piezoelectric field in the photoluminescence spectra is reported. [ABSTRACT FROM AUTHOR]

The effects of γ-ray irradiation (10, 100 kGy) on Gd3+-doped phosphate glass were evaluated. Glass irradiated at 100 kGy was characterized alongside the pristine by differential scanning calorimetry, Fourier transform-infrared spectroscopy and Raman scattering, wherein a lack of alteration in thermal and structural properties was supported. Yet, absorption bands developed around 500 nm with γ-ray dose indicating phosphorus oxygen hole center defects. Optical band gap and Urbach energies exhibited decreasing and increasing trends, respectively, reflecting the influence of trapped electrons and increased disorder/defects. By exciting γ-irradiated samples at 265 nm, blue radio-photoluminescence was observed where intensity increased with dose. Decay curves measured monitoring 415 nm emission showed first-order kinetics suggested to arise from phosphorus electron centers. Emission from Gd3+ was quenched with gamma-ray dose while the 6P7/2 emitting state lifetimes decreased. Correlations between Gd3+ emission intensities and lifetimes with optical band gaps suggest electron center defects perform as ‘energy sinks’.

In the present paper, a single host phosphor for a white light emitting diode (W-LED) Sr3(VO4)2:Eu3+, prepared by the co-precipitation method and combustion one, has been reported. Formation of the compound was confirmed by studying the X-ray diffraction pattern. The photoluminescence (PL) properties were studied by fluorescence spectrophotometer F-7000. The Sr3(VO4)2:Eu3+ exhibited a broad emission band covering the entire visible region centered at 520 nm wavelength and a sharp peak at 613 nm, when excited by 350 nm. The excitation spectrum at 520 nm emission wavelength was found to be suitable for pc-W-LED application.

The complete molecule of the title compound, C42H42N4O2, is generated by a crystallographic centre of symmetry. The pendant heptyl chains adopt extended conformations and the dihedral angle between the pyrrole and pyridine rings is 8.18 (15)°. In the crystal, the molecules are arranged in columnar stacks propagating in the [010] direction via slipped aromatic π–π stacking interactions.

The work reports a number of results on the dynamics of swelling and inferred nanostructure of the ion-exchange polymer membrane Nafion in different aqueous solutions. The techniques used were photoluminescent and Fourier transform IR (FTIR) spectroscopy. The centers of photoluminescence were identified as the sulfonic groups localized at the ends of the perfluorovinyl ether (Teflon) groups that form the backbone of Nafion. Changes in deuterium content of water induced unexpected results revealed in the process of polymer swelling. In these experiments, deionized (DI) water (deuterium content 157 ppm) and deuterium depleted water (DDW) with deuterium content 3 PPM, were investigated. The strong hydration of sulfonic groups involves a competition between ortho- and para-magnetic forms of a water molecule. Deuterium, as it seems, adsorbs competitively on the sulfonic groups and thus can change the geometry of the sulfate bonds. With photoluminescent spectroscopy experiments, this is reflected in the unwinding of the polymer fibers into the bulk of the adjoining water on swelling. The unwound fibers do not tear off from the polymer substrate. They form a vastly extended "brush" type structure normal to the membrane surface. This may have implications for specificity of ion transport in biology, where the ubiquitous glycocalyx of cells and tissues invariably involves highly sulfated polymers such asheparan and chondroitin sulfate. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC), as a wide-band gap semiconductor, plays an important role in high temperature and high-power devices, and the spin defect has great application prospect in quantum technology. Divacancy in SiC (V C V Si , VV) has attracted more and more attention. There are a lot of experimental studies on color center preparation by ion implantation, but the mechanism of atomic scale defects in the experimental preparation process is not fully understood. EPI epitaxial 4H–SiC was implanted with 250 keV proton at room temperature under three fluence of 1E14 cm−2, 1E15 cm−2, 1E16 cm−2. Defects of implanted 4H–SiC samples were characterized by photoluminescence spectrum and electron paramagnetic resonance (EPR). The existence of the optimal implantation fluence for V Si and V C V Si (VV) color centers by hydrogen ion implantation was found. Molecular dynamics (MD) simulation by considering the ionization energy loss for swift ion implantation were used to study the defect distribution and transformation at atomic-scale during hydrogen ion implantation and post-annealing. The optimal implantation fluence was found and confirmed by comparing the atomic-scale implantation simulation with the experimental results. In the annealing simulation, the optimal annealing temperature for the color centers in 4H–SiC was verified, and its formation mechanism was analyzed by accurately calculating the defect transformation during the annealing process. Finally, in order to accurately control the depth of color center in 4H–SiC, dual ions implantation of carbon and proton has been studied to realize the optimal divacancy yield by SRIM and MD simulations. Molecular dynamics simulation results showed that low-fluence C pre-implantation is helpful to improve the color center yield for the dual ions implantation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Preparation of high quality pristine and nitrogen-doped Cu 2 O films on Au(111) and Pt(111). • Thorough surface-science analysis of the doped films by XPS, STM, LEED and PL spectroscopy. • Measuring the thermal stability of the N-dopants in the Cu 2 O matrix. • Identifying O substitutional sites as primary binding positions of the N-atoms. • Determining the nitrogen desorption temperature to 500 K, too low for practical applications. Nitrogen doping of Cu 2 O films grown on Au(111) and Pt(111) supports was explored by a variety of surface-science techniques, including electron-diffraction, X-ray photoelectron-spectroscopy (XPS), scanning tunneling microscopy and photoluminescence spectroscopy (PL). The films were prepared by Cu vapor deposition and high-pressure oxidation at 50 mbar O 2. Nitrogen was inserted by adding N 2 to the reactive gas or via sputter doping. Only the latter resulted in a clear N 1s signal in XPS, compatible with the insertion of N-atoms at O substitutional sites. The N-doping caused an overall degradation of the oxide lattice and suppressed the formation of the (√3×√3)R30° surface reconstruction observed on pristine Cu 2 O(1 1 1). Moreover, the oxide Fermi level shifted from the valence-band top into the band gap, indicative for a reduced p-type conductivity of the sample upon doping. The N-dopants featured low thermal stability and largely desorbed at around 500 K, leaving behind a pronounced 850 nm PL peak due to O vacancy emission. Our findings indicate that the N-atoms initially occupy O substitutional sites but get removed easily at moderate temperature, casting doubts whether N-doping is a suitable pathway to improve the conductance and luminescence behavior of Cu 2 O. [ABSTRACT FROM AUTHOR]