PL Emission Peak Research Articles

Silver-loaded In2S3-CdIn2S4@X(X=Ag, Ag3PO4, AgI) ternary heterostructure nanotubes treated by electron beam irradiation with enhanced photocatalytic activity

Ternary heterostructure nanotubes of In2S3-CdIn2S4@X(X = Ag, Ag3PO4, AgI) were synthesized with enhanced photocatalytic activity for efficiently degrading pollutants. Electron beam irradiation was employed to artificially introduce interface defects to the heterostructure nanotubes. The experimental results for degrading carmine and Cr6+ under visible light irradiation showed that the photocatalytic efficiency of In2S3-CdIn2S4 was improved to some extent by the introduction of silver compounds. DRS results confirmed that the band gaps of In2S3-CdIn2S4 were reduced to 1.62 eV and 1.58 eV by introducing Ag3PO4 and AgI, respectively. Interestingly, the band gap of In2S3-CdIn2S4@AgI after electron beam irradiation was further reduced to 1.56 eV, resulting in that the degradation time of both Cr6+ and carmine by In2S3-CdIn2S4@AgI after high-energy electron beam irradiation was shortened to only 5 min. The XRD spectra of the photocatalysts after five cycles could maintain the original crystal form to a large extent. The OH stretching vibration peaks of In2S3-CdIn2S4@AgI after electron beam irradiation at 3387 cm−1 became wider and sharper, thus indicating that the number of free hydroxyl groups on the heterostructure surface significantly increased. PL results showed that electron beam irradiation could significantly reduce the PL emission peak and enhance the utilization of photogenerated charge carriers. EIS results further confirmed that In2S3-CdIn2S4@AgI processed by electron beam irradiation had higher photogenerated electron-hole separation efficiency. Based on the experimental results, a feasible reaction pathway and photocatalytic mechanism for the degradation of carmine was investigated. ESR results showed that the main active groups in the whole photocatalytic system were •O2– and h+.

Highly crystalline perovskite BaSnO3 nanopowder synthesised using hydrothermal technique

Perovskite cubic Barium Stannate (BaSnO3) with wide bandgap and high electron mobility at room temperature has been synthesized through hydrothermal technique. Highly pure BaSnO3 nanoparticles with average crystallite size of 25 nm and lattice parameter equal to 4.208 Å have been obtained after heat treating the sample to 1000 °C. The morphology and composition of the samples investigated using SEM, TEM and EDAX shows the presence of elongated cubical structure without any trace of impurities. Optical absorption spectrum exhibits strong absorption in the UV region and PL emission peak is centred at 438 nm in the visible spectral region.

High energy (150 MeV) Fe11+ ion beam induced modifications of physico-chemical and photoluminescence properties of high-k dielectric nanocrystalline zirconium oxide thin films

Abstract This work presents the influence of dominated electronic energy loss over nuclear energy loss induced by swift heavy ion (SHI) irradiation on the physico-chemical, optical and other properties of RF grown zirconium oxide (ZrO2) thin films. For this purpose, thin films of ZrO2 grown on glass substrate were irradiated by 150 MeV Fe11+ ions with a range of fluence from 2E12 to 5E13 ions/cm2 to understand the mechanism of induced modifications and defects generation. The XRD results confirmed that the virgin and irradiated ZrO2 thin films were crystalline in nature with monoclinic and tetragonal structure. The crystallite size varied from 19.93 nm to 46.43 nm with varying ion fluence. Strain, dislocation density and stacking fault were used to investigate the changes in structural parameters. Tauc's plot method was employed for the quantitative evaluation of optical energy band gap (Eg) that exist in the range of 4.45–4.62 eV. The transmittance (%) of the virgin and Fe11+ ions irradiated samples was determined in the range of 35.69–66.09% using UV–Vis. spectroscopy. Further, the refractive index was determined using different methods significantly depends on the optical band gap. The broad PL emission peaks were obtained at 375 nm and 440 nm with the excitation wavelength (λex.) of 300 nm. The variation in PL intensity with increasing ion fluence was attributed to the creation or annihilation of primary or complex defects. FTIR spectroscopy was employed for the analysis of chemical modifications in vibrational bonds of samples and the band obtained 660 cm−1was assigned to the asymmetrically coupled Zr–O–Zr stretching which presents the strong vibration in samples. The band intensity increased up to the fluence 5E12 ions/cm2 and decreased at a higher fluence of 1E13 ions/cm2. Rutherford backscattering spectroscopy technique was used to determine the thickness (165 nm) of the samples.

Solution-Processed Mg-Substituted ZnO Thin Films for Metal-Semiconductor-Metal Visible-Blind Photodetectors

The effects of Mg on the microstructural, optical, and electrical properties of sol-gel derived ZnO transparent semiconductor thin films and the photoelectrical properties of photodetectors based on MgxZn1−xO (where x = 0 to 0.3) thin films with the metal-semiconductor-metal (MSM) configuration were investigated in this study. All the as-synthesized ZnO-based thin films had a single-phase wurtzite structure and showed high average transmittance of 91% in the visible wavelength region. The optical bandgap of MgxZn1−xO thin films increased from 3.25 to 3.56 eV and the electrical resistivity of the films rose from 6.1 × 102 to 1.4 × 104 Ω·cm with an increase in Mg content from x = 0 to x = 0.3. Compared with those of the pure ZnO thin film, the PL emission peaks of the MgZnO thin films showed an apparent blue-shift feature in the UV and visible regions. The photo-detection capability was investigated under visible, UVA, and UVC light illumination. Linear I-V characteristics were obtained in these ZnO-based photodetectors under dark and light illumination conditions, indicating an ohmic contact between the Au electrodes and ZnO-based thin films. It was found that the pure ZnO photodetector exhibited the best photoconductivity gain, percentage of sensitivity, and responsivity under UVA illumination. Under UVC illumination, the photoconductivity gain and percentage of sensitivity of the MgZnO photodetectors were better than those of the pure ZnO photodetector.

Growth of perovskite nanocrystals in poly-tetra fluoroethylene based microsystem: on-line and off-line measurements

Cesium lead halide perovskite nanocrystals are photoelectric nanomaterials that have potential applications in a variety of areas due to their excellent photoelectric and tunable photo luminescent properties. In this work, we investigate the synergetic effects of reaction temperature, reaction-capillary length and flow rate on the growth kinetics of perovskite nanocrystals in a PTFE-based microsystem and the photoluminescence characteristics of the perovskite nanocrystals both on-line and off-line. The on-line measurement finds that increasing the reaction temperature leads to the increase of the wavelength of the PL emission peak of the synthesized nanocrystals and reduces the average size of the perovskite nanocrystals synthesized in long reaction-capillaries. The intensity of the PL emission peak of the nanocrystals synthesized at different reaction temperatures decreases with the increase of the flow rate. The off-line measurement reveals that increasing the flow rate generally leads to the blueshift of the PL emission peaks and the decrease of the average size of the perovskite nanocrystals synthesized at the reaction temperature of 160 °C in the capillary length of 60 cm. Increasing temperature leads to the increase of the emission wavelength of the perovskite nanocrystals from 560 to 608 nm. The temperature dependence of the average size of the synthesized nanocrystals with the same synthesis conditions at different temperatures can be described by the Arrhenius relationship with an activation energy of 8.54 kJ mol−1. Five different cross-sections of the synthesized perovskite nanocrystals are observed, including rhombus, hexagon, rectangle, square and quadrangle with three of them being observed for the first time.

Bulk luminescent solar concentrators based on organic-inorganic CH3NH3PbBr3 perovskite fluorophores

In this paper, we report characterization and performance results of lead bromide perovskite luminescent solar concentrator. CH3NH3PbBr3 fluorophores are synthesized by sonication method and examined by their X-ray diffraction pattern and scanning electron microscopy. Synthesized perovskite shows excitonic absorption at 524 nm and PL emission peak located at 532 nm with a Stokes shift around 8 nm. Micron-sized fluorophores are dissolved in prepared solutions and uniformly embedded in PMMA host with 0.006–0.120%wt concentration. Then, Fabricated devices are cut into 50 × 30 × 5 mm cuboid shapes and placed in a mirror surrounded configuration with an attached photovoltaic cell. Fabricated device is put under standard AM1.5 illumination and the output spectrum from the concentrator is acquired. Re-absorption in the samples is also measured by variable optical path method, showing red-shifts up to 13 nm in the output spectrum. Spatially resolved photoluminescence maps and optical efficiencies are also presented for each sample. Plus, a Monte-Carlo ray tracing algorithm is developed to assist better understanding the experimental results. Stability of fabricated samples are evaluated under high intensity UV illumination, reporting efficiency reduction around 15% after 24 h. Finally, Comparing current-voltage characterization of the attached photovoltaic cell reveals optimized efficiency enhancement in the 0.04%wt sample above 65%.

A promising Ag2CrO4/LaFeO3 heterojunction photocatalyst applied to photo-Fenton degradation of RhB

ABSTRACTAg2CrO4 nanoparticles (10–35 nm) were assembled onto LaFeO3 nanoparticles (20–60 nm) via a facile chemical precipitation method to form novel Ag2CrO4–LaFeO3 heterojunction composite photocatalysts. The prepared Ag2CrO4–LaFeO3 composites were characterized by XRD, SEM, TEM, XPS, BET, UV-vis DRS, PL spectroscopy and EIS and photocurrent response. The TEM result clearly shows that Ag2CrO4 particles are decorated onto LaFeO3 particles to form Ag2CrO4–LaFeO3 heterojunction. Compared to bare LaFeO3, the 10%Ag2CrO4-LaFeO3 composite exhibits a slightly increased BET specific surface area, increased photocurrent density, decreased charge-transfer resistance and decreased PL emission peaks. Using simulated sunlight as the light source and in the presence of H2O2, the photo-Fenton performance of the composite photocatalysts toward the degradation of RhB was investigated, revealing that they manifest significantly enhanced photo-Fenton degradation of RhB when compared with bare LaFeO3 and Ag2CrO4. Among the composite photocatalysts, 10%Ag2CrO4–LaFeO3 exhibits the highest photo-Fenton activity, which is about 3.1 and 2.5 times higher than that of bare LaFeO3 and Ag2CrO4, respectively. This is attributed to the fact that the composite photocatalysts have highly efficient separation of photogenerated electron–hole pairs due to the formation of Ag2CrO4–LaFeO3 heterojunctions. Active species trapping experiments and ·OH detection experiments were carried out, from which it is concluded that ·OH radicals are the dominant reactive species causing the dye degradation. A synergistic mechanism was proposed to elucidate the enhanced photo-Fenton activity of Ag2CrO4–LaFeO3 heterojunction composites.

Modulating Surface Morphology Related to Crystallization Speed of Perovskite Grain and Optical Semiconductor and Crystallization Properties of the Absorber Layer Under Controlled Doping of Potassium Ions for Solar Cells.

Perovskite thin films with excellent optical semiconductor and crystallization properties and superior surface morphology are normally considered to be vital to perovskite solar cells (PSCs). In this paper, we systematically survey the process of modulating surface morphology and optical semiconductor and crystallization properties of methylammonium lead iodide film by controlling doping of K+ for PSC prepared in air and propose the mechanism of large K+-doped perovskite grain formation related to crystallization speed. The increase in the crystallization speed leads to the production of large grains without localized-solvent-vapor (LSV) pores via moderate doping of K+, and the exorbitant crystallization speed induces super large grains with LSV pores via excessive doping of K+. Furthermore, the semiconductor properties (absorption band edge wavelength, PL emission peak wavelength, energy band gap) of perovskite film can be significantly tuned by controlled doping of K+. The investigation of the detailed process of modulating surface morphology and semiconductor properties of perovskite thin film by controlled doping of K+ may provide guidance and pave the way for superior component design of absorption materials for cost-efficient PSCs.

Valley-Selective Linear Dichroism in Layered Tin Sulfide

Valley-related physics, optics, and electronics have been extensively investigated in transition metal dichalcogenides with a honeycomb lattice such as molybdenum disulfide. Their photoemission properties exhibit a circular dichroism due to energy degenerate but inequivalent valleys located at K and K′ in momentum space. Recently linear dichroism was observed in few-layer black phosphorus with highly anisotropic in-plane optical properties. Here, we report a novel valley-selective linear dichroism of the photoluminescence in layered thin-film tin sulfide (SnS). We identified two PL emission peaks, exhibiting an orthogonal linear dichroism, arising from two inequivalent valleys in the energy band. The photon emission from the Γ-X valley is completely x-polarized, while in contrast, the photon emission from the Γ-Y valley is purely y-polarized. This unique valley-selective linear dichroism in SnS is further confirmed by the band-edge absorption measurements along the Γ-X and Γ-Y directions, respectively. Ou...

Perovskite quantum dots as fluorescent materials for multi-colored lighting

Halide perovskite quantum dots (PQDs) have been intensively studied because of their superior optical properties and have great potential applications in laser, display technology and light-emitting diodes (LEDs). Presently, high-efficiency green emissive CH3NH3PbBr3 PQDs have been successfully fabricated. However, the synthesis of stable iodide-based CH3NH3PbX3 (MAPbX3 (X = Cl, Br, I), MA = CH3NH3) QDs still faces significant challenges because they are sensitive to the moisture in open air. Herein, we investigated the effect of the solvent and ligand on the growth of the as-prepared MAPbBr3 and MAPbI3 sample, mainly involved in the volume ratio of N,N-dimethylformamide (DMF) and γ-butyrolactone (GBL) and the amount of n-octylamine in toluene. The results show that the low volume ratio of DMF and GBL is beneficial to prepare highly luminescent, stable and full-colored MAPbX3 PQDs in open air. Besides, the PL emission peak of MaPbBr3 PQDs can be adjusted from 430 to 513 nm via precisely controlling the amount of n-octylamine in toluene because of quantization. The obtained MAPbX3 PQDs show high quantum yield and a wide range of tunable light emission from ultraviolet to near-infrared region. The MAPbX3 PQDs, especially iodide-based MAPbX3 PQDs, obtained from this method remain stable more than 3 months at ambient condition. We further demonstrated the multi-colored LEDs by using different color emissive MAPbX3 PQDs as color converters and being subjected to excitation through a blue GaN chip. Furthermore, MAPbX3 PQDs are expected to show interesting nanoscale optical properties and have great potential applications in electroluminescence devices, lasers and optical sensors.

Photocatalytic and photo-induced disinfection activities of sol-gel synthesized CeO2–SnO2:TM (TM= Co, Ni and Mn) nanocomposites: Relation between physical properties and their performance

CeO2-SnO2 and transition metals (Co, Ni and Mn)-doped CeO2–SnO2 nanoparticles (NPs) were prepared by organic sol-gel route. X-ray diffraction analysis and Williamson–Hall isotropic strain method indicated that the crystallite size of cubic fluorite structure decreased by transition metals doping from 12.6 to 4.7 nm. The optical bandgap of CeO2–SnO2 nanocomposites decreased from 3.21 to 2.91 eV for CeO2–SnO2:Mn sample. The blue-green PL emission peak of NPs enhanced with doping due to increased Ce3+ and oxygen vacancies content. Photocatalytic degradation of rhodamine B (RhB) in aqueous solution under UV irradiation in the presence of CeO2–SnO2 NPs was investigated. Transition metals doping improved The photodegradation ratio of CeO2–SnO2 and the CeO2–SnO2:Mn nanoparticles had the highest efficiency compared to other samples. More interesting, evaluation of antibacterial and photo-induced disinfection activity of CeO2–SnO2:TM NPs against clinically important bacteria manifested the highest antibacterial potential for CeO2–SnO2:Mn compared to the other NPs. It is therefore proposed that enhanced oxygen vacancies as well as high surface area assist to produce reactive oxygen sites (ROHs) which are accountable for photocatalytic and photo-induced disinfection activities.

Carrier confinement effects of InxGa1-xN/GaN multi quantum disks with GaN surface barriers grown in GaN nanorods

Structural and optical properties of InxGa1-xN/GaN multi quantum disks (QDisks) grown on GaN nanorods by molecular beam epitaxy have been investigated by transmission electron microscopy and micro-photoluminescence (PL) spectroscopy. Two types of InGaN QDisks were grown: a pseudo-3D confined InGaN pillar-type QDisks embedded in GaN nanorods; and QDisks in flanged cone type GaN nanorods. The PL emission peak and excitation dependent PL behavior of the pillar-type Qdisks differ greatly from those of the flanged cone type QDisks. Time resolved PL was carried out to probe the differences in charge carrier dynamics. The results suggest that by constraining the formation of InGaN QDisks within the centre of the nanorod, carriers are restricted from migrating to the surface, decreasing the surface recombination at high carrier densities.

Ferrimagnetism in cobalt ferrite (CoFe2O4) nanoparticles

Ferrimagnetic cobalt ferrite (CoFe2O4) nanoparticles were synthesized by employing co-precipitation method. Product physico-chemical and magnetic properties with respect to cetyl trimethylammonium bromide (CTAB), hexamethylenetetramine (HMT) and polyethylene glycol (PEG-400) surfactants were investigated. XRD pattern and Raman characteristic active modes revealed the cubic cobalt ferrite structure formation. SEM images explored spherical shaped product with different particle size. Identified strong PL emission peaks confirmed the product quality. IR metal oxygen vibration at 615 and 426 cm−1 revealed tetrahedral and octahedral site of cobalt ferrite system. Product electrochemical behavior was found to be size dependent and high specific capacitance was observed using CTAB. Room temperature ferrimagnetic behavior was confirmed through VSM studies. High saturation value as 66 emu/g was found using PEG. Particles with larger crystallite and particle size exhibited improved magnetic behavior.

Efficient electrochromic performance of anatase TiO2 thin films prepared by nebulized spray deposition method

Anatase TiO2 thin films with high optical modulation, better reversibility, fast switching time, and enhanced coloration efficiency were prepared by nebulized spray pyrolysis technique. X-ray diffraction study confirmed the formation of anatase phase TiO2 in the present work. This inference was substantiated from the Raman active modes of A1g, 2 B1g, and 3 Eg corresponding to O–Ti–O bond in TiO2. The PL emission peak observed at 400 nm is corresponds to the indirect transition (X1b → Γ3) from the conduction band to the valence band. The average reflectance of TiO2 thin films was varied from 31 to 20%. The electrochemical study revealed the excellent performance of TiO2 films with high optical modulation (ΔT = 61%), fast switching kinetics (t b = 1.6 s, t c = 2.4 s), good coloration efficiency (100 cm2 C−1), and better reversibility (86%). The efficient electrochromic behavior of films may be due to the smooth microstructure nature, which provides an easy pathway for the diffusion and charge transfer process of Li+ ions in TiO2 film matrix. The fast transfer of Li+ ion was realized from the electrochemical impedance spectroscopic measurement.

The microstructure, local indium composition and photoluminescence in green-emitting InGaN/GaN quantum wells.

In this work, we analyse the microstructure and local chemical composition of green-emitting Inx Ga1-x N/GaN quantum well (QW) heterostructures in correlation with their emission properties. Two samples of high structural quality grown by metalorganic vapour phase epitaxy (MOVPE) with a nominal composition of x = 0.15 and 0.18 indium are discussed. The local indium composition is quantitatively evaluated by comparing scanning transmission electron microscopy (STEM) images to simulations and the local indium concentration is extracted from intensity measurements. The calculations point out that the measured indium fluctuations may be correlated to the large width and intensity decrease of the PL emission peak.

Quantum dots growing of Mn/ZnO nanowires and optimizing the optical properties

Mn-doped zinc oxide (ZnO) nanostructures with different manganese concentrations along with high structural and optical quality were grown through a simple method without using any metal catalysts and through the source quantum dots of the nanowires (ZnO and MnO2). The cross section of the prepared nanowires has been a hexagon with a diameter between 35 and 50 nm and a length between 3 and 6 μm. The surface morphology of the samples was characterized by scanning electron microscopy. The results of the x-ray diffraction analysis showed the wurtzite structure for the prepared samples with a strong preferred peak (002). The energy dispersive x-ray spectra showed a high percentage of Mn at the tip of the samples, and the x-ray photoelectron spectroscopy showed the spectra of MnO2 in the structure of the nanowires. These wires produced a large PL emission peak in the ultraviolet (UV) region and a relatively high peak in the visible region. With the increase of the doping percentage, the intensity of the visible emission increased, and this amount reached to the highest peak intensity and maximum quantum yield (QY=39%) at 5% of the dopant as the quenching point. The UV peak of the Mn/ZnO nanowires amounts to 11-nm blueshifted with respect to pure ZnO nanowires confirmed by the UV–visible absorption spectra.

Defect Activated Photoluminescence in WSe2 Monolayer

Defects in transition metal dichalcogenides (TMDs) play an important role in tailoring electrical and optical properties. Here we employ Ar+ plasma to controllably generate active defects in WSe2 monolayers to tune their optical properties. Two defect-activated PL emission peaks are emerging in the low temperature PL spectra of WSe2 monolayer treated with Ar+ plasma. These emissions are attributed to the recombination of excitons bound to different types of structural defects. The shallow level emission originates from the recombination of excitons at chalcogen vacancies, while the deep level emission might arise from other types of defects, such as transition metal vacancies, cluster of vacancies, rotational defects, or antisite defects. Our results demonstrate that Ar+ plasma treatment is an effective approach to induce desirable defects in TMDs monolayers and PL spectroscopy is an efficient method to investigate these defects.

Transparent conductive F-doped SnO2 films prepared by RF reactive magnetron sputtering at low substrate temperature

To obtain highly transparent conductive F-doped SnO2 films by magnetron sputtering at low substrate temperatures, a new method of sputtering high-density SnF2–Sn target in Ar + O2 atmosphere was adopted in the present study. The structural, electrical, and optical properties of the films prepared were investigated as a function of O2 flux. The results indicate that the films shows SnO2 phase only at O2 flux above a critical value (0.8 sccm), and the crystallinity of SnO2 phase is improved with increasing O2 flux. The resistivity of the films steeply decreases once O2 flux is above the critical value, but it greatly increases as O2 flux is too high. Only in intermediate range of O2 flux, the films with low resistivity can be obtained. As O2 flux is above the critical value, both the transmittances in visible light range and E g of the films show steeply increase, and the PL spectra of the film show distinct emission characteristics. Furthermore, the position and intensity of PL emission peaks are similar when O2 flux is above the critical value, and the emission mechanism can be attributed to electron transitions mediated by defect levels in the bandgap, such as V O and F O. Just because of formation of SnO2 phase in the films and existence of relatively larger amount of V O and F O, the films show low resistivity and high transmittance at suitable O2 fluxes.

Synthesis and characterization of Indium doped Lead chalcogenides(PbSe)100−xInx thin films composed of QDs

As-prepared samples of (PbSe)100−xInx(x = 0, 5, 10 and 20) have been synthesized by melt-quenching method and their thin films have been deposited onto glass substrates(at 150 K) by thermal evaporation method. The structural studies of as-deposited thin films have been carried by using HRTEM, HRSEM and XRD analysis. These studies suggest that as-deposited thin films composed of aggregated cubic QDs and polycrystalline structure of the samples. The estimated size of the particles as suggested by the SEM images is found nearly consistent with that of most probable size (6–8 nm for 40% of QDs) as suggested by the TEM-histogram analysis. Due to induced-strain in the lattice, the particles' size is found reducing with increase in In content, this trend is verified by HRSEM images and full width half maxima values of XRD peaks. The QDs of the samples have been excited at wavelength of 300 nm and PL-emission peak has been observed at 370 nm. Blue shift and peak broadening effects are observed with increase in In content. These are the indications of quantum size effect and wide size distribution of the particles with increase in dopent concentration. Optical absorptions(200–900 nm) at room temperature, suggest a direct bandgap that increases with increase in doping content. This is the indication of the presence of defect states and high density of localized states. Width of the urbach tails in the localized states shows a narrowing trend with increase in doping content. This may be due to decrease in band tails which results in widening of optical band gap.

Annealing temperature dependent non-monotonic d0 ferromagnetism in pristine In2O3 nanoparticles

Cubic bixbyite In2O3 nanoparticles with room temperature d0 ferromagnetism were prepared by sol-gel method with the air annealing temperature ranging from 500 to 900°C. X-ray diffraction, X-ray photoelectron spectroscopy, Raman-scattering and photoluminescence were carried out to demonstrate the presence of oxygen vacancies. The lattice constant, the atomic ratio of crystal O and In, the Raman peak at 369cm−1, the PL emission peak at 396nm and the saturation magnetization of d0 ferromagnetism all had a consistent non-monotonic change with the increasing annealing temperature. With further considering the relation between the grain size and the distribution of oxygen vacancies, we think that d0 ferromagnetism in our samples is directly related with the singly charged oxygen vacancies at the surface of In2O3 nanoparticles.