Intensity Of Photoluminescence Spectra Research Articles

Detection of Intermediate in Ammonia Oxidation Reaction Using Aggregation-Induced Emission Phenomenon

Ammonia electro-oxidation reaction (AOR) is a vital reaction for solving energy and environment problems as it is the anodic reaction in direct ammonia fuel cells (DAFCs), ammonia electrolyzer and in the remediation of wastewater containing ammonia.1-2 Designing high-performance electrocatalysts for AOR requires thorough understanding of mechanism and intermediates produced. Techniques like in-situ FTIR have provided information about intermediates produced during AOR in aqueous alkaline media.3-4 However, the mechanism is still not well understood and more proof of exact intermediates are needed. Furthermore, these in-situ methods are complex with multiple procedures requiring extreme precision.N2Hx is an important intermediate in the dimerization step according to Gerischer and Mauerer mechanism. In this work, aggregation-induced emission (AIE) phenomenon was used for the first time to target and detect hydrazine (N2H4) as an intermediate during AOR using commercial Pt/C as electrocatalyst. Tetraphenylethene-CHO (TPE-CHO) molecule as AIEgen was used for this purpose. Combination of photoluminescence (PL) spectra showing turn-off fluorescence along with the electrochemistry results illustrated the presence of hydrazine as an intermediate. In Figure 1, fluorescence spectra in THF/water mixture with 90% of water fractions for different electrocatalyst loading keeping the AIE concentration same is depicted. It was observed that with increase in catalyst concentration, PL spectra intensity decreased considerably indicating towards the desired reaction of intermediate produced during reaction with the already present AIE on GC electrode. Control experiments using graphene and TPE were performed to elucidate the results further. Mass spectra of the product formed after reaction between hydrazine hydrate and TPE-CHO was obtained and compared with the one obtained during electrochemical reaction. A very simple and novel method for detection of an intermediate, hydrazine in AOR using AIE phenomenon is demonstrated opening new strategy for mechanism understanding of an electrochemical reaction. Figure 1. Fluorescence spectra in THF/water mixture with 90% of water fractions for different electrocatalyst loading keeping the AIE concentration same.

Synthesis and Characterization of Zinc Oxide Nanoparticles (ZnO NPs) in Powder and in Thin Film using Corn Husk Extract via Green Chemistry

Abstract:In this study, zinc oxide nanoparticles (ZnO NPs) in powder and in thin film were successfully synthesized first time using an eco-friendly, simple and cost effective green synthesis method mediated by corn husk (Zea mays) extract as an effective chelating agent, and zinc nitrate hexahydrate as precursor. Diverse characterizations techniques such as High Resolution – Scanning Electron Microscopy (HR-SEM), Energy Dispersive X- rays Spectroscopy (EDS), X-Rays Diffraction (XRD), and UV – Vis – NIR spectroscopy as well as Photoluminescence (PL) were investigated to confirm ZnO NPs nature. For the ZnO NPs powder, highly crystalline ZnO nanoparticles (ZnO NPs) annealed at 500°C which are 48.635 nm in particles size were characterised by HR-SEM and XRD analysis. The structure morphology and the constituents of the resultant ZnO powder were investigated respectively by HR-SEM and EDS. UV – Visible spectroscopy analysis was investigated on the optical band gap of ZnO NPs, which was calculated to be 3.31 eV. This result indicates that ZnO NPs can be used in metal oxide semiconductor-based devices. For the ZnO NPs thin film, XRD patterns of hexagonal wurtzite structure with c/a ratio about of 1.60 and μ – parameter of 0.38 were obtained. PL measurements showed a broad emission band in the 380 – 800 nm range, centred at 481 nm. ZnO NPs thin film yielded relatively more intense photoluminescence spectra than the ZnO NPs powder. The intrinsic point defects and defect level transitions responsible for the broad emission are discussed.

Solvothermal growth of aligned SnxZn1-xS thin films for tunable and highly response self-powered UV detectors

In this study, well-aligned SnxZn1-xS (0 ≤ x ≤ 0.12 mol) nanostructured thin films were successfully grown on the glass substrate by a solvothermal method for ultraviolet detector applications. XRD results revealed a hexagonal wurtzite structure for all the SnxZn1-xS thin films. Through structural and morphological studies, as the Sn-content increases, the c-axis orientation became stronger. A comprehensive investigation of the morphological evolution also confirmed a considerable influence of Sn2+ incorporation on the growth mechanism and shape of the SnxZn1-xS nanostructures. The optical measurements indicated that as the Sn-content increases, a linear relationship between the band gap and Urbach energy was found, in which the band gap energy experienced a significant decrease from 4.20 to 3.83 eV; whereas the Urbach energy was dramatically broadened. A gradual increase was observed in the intensity of photoluminescence spectra, in which three prominent emission peaks were found, indicating a successful formation of the SnxZn1-xS nanostructures. The photosensing performance of the samples was studied for the first time. The ultraviolet detectors based on the Au/SnxZn1-xS thin film junctions featured an excellent rectification behavior and attractive photovoltaic effect under UVB exposure. The enhancing effects of annealing treatment on the photoelectric behavior of the samples were also noted. The photoresponse characteristics of the self-powered ultraviolet detectors exhibited a high Ion/Ioff ratio > 103 and a fast photoswitching speed with superior stability and reproducibility at zero voltage. Additionally, notable photosensitivity and detectivity of more than ∼20 times are achieved at the self-powered mode.

Flexible polymer composite films incorporated with Li-ion/reduced graphene oxide: excellent optical and photoluminescence performance

A flexible polymer composite film (PL-rGO) was prepared from reduced graphene oxide (rGO) (derived from graphite) and lithium phosphate (Li3PO4) incorporated in a pale yellow colored polystyrene sulfonic acid (PSSA) polymer by solution casting method. The resulting flexible translucent PL-rGO composite films were obtained with smooth surface and thickness in the range of 2–3 µm. The optical and photoluminescence properties of PL-rGO were explored in the present study. The intensity of photoluminescence spectra at excitation band ∼ 320 nm increases with significant broadening with varying concentration of rGO in the matrix. The evaluated direct and indirect energy bandgap of PL-rGO composite from optical absorbance is in the range of 3.06 ~ 3.26 eV. These results from optical properties for PL-rGO composite indicate the accurate tailoring of the composite by changing the rGO volume fraction.

Enhanced photocatalytic performance of Cu2O nano-photocatalyst powder modified by ball milling and ZnO

In this paper, a ball milled Cu2O-ZnO nano-photocatalyst with good photocatalytic performance in visible light range was prepared. Effect of ZnO presence and ball milling of Cu2O on the structure, microstructure, optical properties and photocatalytic performance were studied. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), high resolution transmission electron microscopy (HRTEM), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) analysis and UV–Vis spectrophotometer were used as characterization techniques. FESEM results indicated that ball milling of Cu2O changed the morphology of Cu2O-ZnO composite. The uniform formation of ZnO particles with average size of 30 nm over the Cu2O surface was observed. The formation of p-n heterostructure with good contact between Cu2O and ZnO nanoparticles was found by HRTEM image. Ball milling of Cu2O promotes visible light absorption and reduction band gap to 1.9 eV in Cu2O-ZnO photocatalyst. Intensity of PL spectra for the ball milled Cu2O-ZnO photocatalyst was obviously lower. Ball milled Cu2O-ZnO photocatalyst shows the highest photocatalytic activity and degradation efficiency of 98% was obtained for 2 mg/L methylene blue (MB) solution after 240 min. The kinetics of the photodegradation was followed the Langmuir-Hinshelwood (L-H) model and degradation rates were decreased by increase of MB concentration. In the case of ball milled Cu2O and presence of ZnO, the MB degradation kinetics was two times faster.

Growth of GaP1 − x − yAsyNx on Si substrates by chemical beam epitaxy

Chemical beam epitaxy has been used to grow layers of GaP1 − xNx, GaP1 − yAsy, and nearly lattice-matched layers GaP1 − x − yAsyNx on Si substrates. To address the issue of antiphase domain generation associated with the growth of polar semiconductors on Si, misoriented Si(001) substrates have been used combined with a carefully designed GaP buffer layer growth. The reflection high-energy electron diffraction pattern exhibits a (2 × 4) surface reconstruction after GaP buffer layer and GaP(As,N) graded layer growth, indicating the good surface quality and planarity of the grown layers. Sample composition was obtained by simultaneous acquisition of Rutherford backscattering spectrometry and nuclear reaction analysis, indicating a linear dependence of N and As mole fractions on the flux of their respective precursor. GaP1 − x − yAsyNx layers grown on Si substrates have a lattice mismatch not larger than ±0.005 for N contents in the range 0.02 < x < 0.05. High-resolution X-ray diffraction reciprocal space maps demonstrate a good crystalline quality. Intense photoluminescence spectra have been measured in all GaP1 − xNx and GaP1 − x − yAsyNx layers, as it is expected for direct bandgap materials. Two wide overlapped emission peaks are observed in all the spectra, most likely related to near bandgap recombination. The position of the higher energy peak for GaP1 − xNx and GaP1 − x − yAsyNx layers has been compared to bandgap energy calculations using the band anticrossing model, showing good agreement.

Optical properties of chitosan/hydroxyl-functionalized graphene quantum dots thin film for potential optical detection of ferric (III) ion

In this research, the preparation of chitosan and hydroxyl-functionalized graphene quantum dots (HGQDs) composite has been described. The spin coating technique was used to prepare the chitosan/hydroxyl-functionalized graphene quantum dots (Cs/HGQDs) thin film. The Cs/HGQDs thin film was then characterized using the Fourier transform infrared spectroscopy which confirmed the existence of amino groups, carboxylic acid groups, carboxyl groups and hydroxyl groups in Cs/HGQDs. UV–Vis absorption spectroscopy and photoluminescence (PL) were used to study the optical properties of the thin film. The absorption of Cs/HGQDs thin film was high with optical band gap of 3.797 eV. The intensity of PL spectra of the thin film was observed around wavelength of 420 nm. The incorporation of Cs/HGQDs thin film with surface plasmon resonance spectroscopy produced positive responses towards the Fe3+ ion solutions of different concentration and it was found that Cs/HGQDs thin film able to detect Fe3+ as low as 0.5 ppm with a sensitivity of 0.11396° ppm−1. Subsequently, Cs/HGQDs layer have high potential as sensing layer to detect Fe3+ due to high affinity of Fe3+ ion towards the thin film with a value of binding affinity constant, K equals to 5.79 ppm−1. Atomic force microscopy was used to observe the surface morphology of the thin film and the result indicates that the thin film is relatively smooth and homogenous which also confirmed the interaction of Fe3+ with the thin film. Thus, Cs/HGQDs thin film shows potential for the detection of Fe3+ in solution.

Zinc tin oxide nanocomposites with nanodiamonds – Preparation, characterization and optical properties investigations

As one of the transparent semiconducting oxides (TCOs), zinc tin oxide (ZTO) has gained a tremendous technological importance owing to its large scale applications, particularly, in opto-electronic devices. Nonetheless, the optical band gap of ZTO is always desired to be tuned, and thus optimized for a particular application. Herein we report upon varying the optical band gap of ZTO nanomaterials by using chemically functionalized nanodiamonds (NDs) as reinforcement for the very first time. ZTO nanocomposites with different weight percent (wt.%) i.e., 5wt.%, 10wt.% and 15wt.% of NDs were prepared by simple solution method, employing poly(methyl methacrylate) (PMMA), prepared in-situ, as structure directing agent (SDA). The crystal structure were established by powder X-rays diffraction (PXRD) analysis. Energy dispersive X-rays spectroscopy (EDX) was used to determine the elemental composition of the samples. The impacts of synthesis method and NDs addition upon the morphology of ZTO nanocomposites were studied by scanning electron microscopy (SEM). SEM revealed that the particle size of ZTO nanocomposites varies as a function of NDs contents. The optical energy band gaps of the resulting nanomaterials were studied by UV–vis diffused reflectance spectroscopy (DRS), and it was observed that the band gap increases with increases NDs contents. However, the absorption intensity decreased with increasing NDs contents, particularly, in the visible region. The optical properties were further investigated by photoluminescence (PL) spectroscopy, and it was revealed that the intensity of PL spectra decreases with increasing NDs contents in the resulting ZTO nanomaterials. This was owed to the passivation of excessive Zn+ by NDs, decreasing the lattice defects which are responsible for deep level emission (DLE).

In-situ synthesis of self Ti3+ doped TiO2/RGO nanocomposites as efficient photocatalyst to remove organic dyes from wastewater under direct sunlight irradiation

Reduced graphene oxide modified titania nanocomposite is successfully synthesized using an inorganic precursor of titania and graphite through a controlled hydrolysis method. Modified Hummers’ method is adopted to synthesize the graphene oxide. XRD analysis indicates that the synthesized anatase titania nanocrystals have crystallite size within the range of 3–10 nm. Microstructural and Raman study confirms the TiO2 nanocrystals are closely packed and in interfacial contacts with graphene oxide sheets respectively. It has been observed that small percentage of graphene oxide loading (5 wt%) on TiO2, some extent influences the textural properties; like, crystallite size, specific surface area, pore volume, etc. The low intense photoluminescence spectra of the nanocomposite reveal slower rate of radiative recombination of the charge carriers. UV-Vis absorption and DRS-spectra illustrates a red shift in absorption peak and a reduced band gap in the nanocomposite, respectively. The existence of Ti3+ and oxygen vacancies into lattice is observed from the XPS analysis. Electrical conductivity in the nanocomposite is found to be higher compared to reference TiO2, as evident from the CIS analysis. Therefore, the combination of reduced graphene oxide and titania in the nanocomposites significantly increases the adsorption aptitude towards organic pollutants (e.g. dyes) which is related to their typical surface properties. Moreover, the incorporation of graphene oxide in the nanocomposites exerts a significant combined effect on the charge transfer dynamics and adsorption, which together provide them with better photocatalytic activity toward rhodamine B and other organic dyes in aqueous solution.

Effect of Sm3+ ions concentration on borosilicate glasses for reddish orange luminescent device applications

Zinc Bismuth Strontium Borosilicate (ZnBiSrBSi) glasses doped with varying concentrations of samarium (Sm3+) ions have been synthesized via melt quenching technique and characterized by using XRD, SEM, optical absorption, excitation, Photoluminescence (PL) and decay spectral measurements. The amorphous nature of the as prepared glass has been confirmed by XRD and SEM measurements. The PL spectra recorded for the as-prepared glasses under 403 nm excitation show four emission bands from 4G5/2 level to 6HJ (J = 5/2, 7/2, 9/2 and 11/2). Among the four emission transitions, 4G5/2 → 6H7/2 transition at 600 nm is having highest intensity. The intensity of PL spectra in the titled glasses increases with increase in Sm3+ ions concentration up to 0.5 mol% and beyond decreases due to concentration quenching. Dexter theory applied to the emission spectral features reveals the energy transfer mechanism between Sm3+- Sm3+ ions as dipole-dipole in nature. The experimental lifetimes measured from the PL decay profiles for the intense 4G5/2 → 6H7/2 transition decreases with increase in Sm3+ ions concentration due to energy transfer between Sm3+-Sm3+ ions. All the aforementioned studies finally reveal that 0.5 mol% of Sm3+ ions in ZnBiSrBSi glasses is optimum in fabricating the reddish orange luminescent devices.

Comprehensive physical studies on nanostructured Zn-doped CdSe thin films

Electrochemically deposited un- and Zn-doped CdSe nanostructures have been examined in this study. An aqueous solution having 3CdSO4·8H2O, SeO2, and various amounts of ZnSO4·7H2O was used to deposition un- and Zn-doped CdSe samples. The X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) with energy dispersive X-ray analysis (EDXA) attachment, atomic force microscopy (AFM), room temperature photoluminescence (PL), and UV–Vis spectroscopy have been served to study the impact of Zn-dopant on the physical characteristics of CdSe thin films. All samples had a cubic crystalline system and their crystallite size was 7–9 nm. The lattice constant (a), unit cell volume (V), and the interplanar distance of CdSe samples were reduced after Zn-doping. FESEM images presented grain-like morphology for all samples. According to AFM results, the surface smoothness of Zn-doped CdSe samples was improved compared to the undoped CdSe sample. Two observed PL emission peaks at 564 and 690 nm were associated with the recombination of electron-hole and the near band emission (NBE) of CdSe, respectively. The intensity of PL spectra of CdSe samples was decreased after Zn-doping, which related to the generation of non-radiative relaxation of electron transition. According to UV–Vis spectroscopy results, the Eg of undoped CdSe sample was 1.73 eV that it reduced to 1.67 eV for Zn-doped CdSe samples. The optical- and electrical conductivity of CdSe thin films have been improved due to Zn-doping. Accordingly, the obtained results confirmed that the Zn dopant plays a key role in the physical properties of nanostructured CdSe thin films.

Photoluminescence investigations on Dy3+ ions doped Zinc Lead Tungsten Tellurite glasses for optoelectronic devices

Dy3+ doped Zinc Lead Tungsten Tellurite (ZnPbWTe) glasses have been synthesized by conventional melt quench method and their luminescence behavior was analyzed using optical absorption, excitation, photoluminescence (PL) and PL decay spectral studies. The Judd-Ofelt (J-O) intensity parameters evaluated from the absorption spectra are used to determine various radiative parameters such as transition probability (AR), branching ratio (βR) and radiative lifetimes (τR) for the prominent emission transitions of Dy3+ions in ZnPbWTe glasses. Under 384 nm excitation, PL spectra recorded for the titled glasses, exhibit two intense peaks; one in yellow at 575 nm and the other one in blue at 483 nm region. Among these two, yellow band (4F9/2 → 6H13/2) is relatively more intense than the blue one (4F9/2 → 6H15/2). The intensity of PL spectra increases up to 1 mol% of Dy3+ ions in ZnPbWTe glasses and beyond concentration quenching is observed. Branching ratios (βR) and emission cross-sections (σse) were estimated for 4F9/2 → 6H13/2 transition to understand the potential utility of these glasses for laser action in visible region. The CIE chromaticity coordinates, color correlated temperature (CCT), color purity and Y/B ratios were also estimated to understand the suitability of these glasses for w-LEDs. The luminescence quantum efficiency evaluated for the titled glasses showing highest value for 1 mol% of Dy3+ ions present in the as prepared glasses. From the measured emission cross-sections, quantum efficiency and CIE coordinates, it was observed that 1 mol% of Dy3+ ions in ZnPbWTe glasses are aptly suitable for optoelectronic devices such as lasers and w-LEDs.

Sol–Gel Synthesis of Fe-Doped TiO2 Nanocrystals

Fe-doped TiO2 powders were synthesized by the sol–gel method using titanium (IV) isopropoxide (TTIP) as the starting material, ethanol as solvent, and ethylene glycol (EG) as stabilizer. These prepared samples were characterized by x-ray diffractometer (XRD), field emission scanning electron microscope (FESEM), Fourier-transform infrared (FTIR) spectroscopy, diffuse reflection spectroscopy (DRS), energy-dispersive x-ray spectroscopy (EDX), and photoluminescence (PL) analyses to study their structure, morphology, and optical properties. The particle size of Fe-doped TiO2 was in the range of 18–39 nm and the minimum crystallite size was achieved for 4 mol.% of Fe. The XRD result of the samples that were doped with Fe showed a tetragonal structure. It also revealed the coexistence of the anatase and rutile phases, and showed that their ratio changed with various molar concentrations of Fe dopant. FTIR spectroscopy showed the presence of the Ti-O vibration band in the samples. PL analysis revealed the PL property in the UV region. Visible irradiation and the intensity of PL spectra were both reduced by doping TiO2 with 3 mol.% of Fe as compared to the pure variety. The spectra from the DRS showed a red shift and a reduction of 2.6 eV in the band gap energy for 4 mol.% Fe-doped TiO2. The optimum level of impurity (4 mol.%) for Fe-doped TiO2 nanoparticles (NPs), which improve the optical and electrical properties by using new precursors and can be used in solar cells and electronic devices, was determined. The novelty of this work consists of: the Fe/TiO2 NPs are synthesized by new precursors from sol–gel synthesis of iron and TTIP using acetic acid-catalyzed solvolysis (original idea) and the optical properties optimized with a mixture of phases (anatase/rutile) of Fe-doped TiO2 by this facile method.

The Reduced Recombination and the Enhanced Lifetime of Excited Electron in QDSSCs Based on Different ZnS and SiO2Passivation

In this study, we focus on the enhanced absorption and reduced recombination of quantum dot solar cells based on photoanodes which were coated by different ZnS or SiO2passivations using the successive ionic layer absorption and reaction methods. The quantum dot solar cells based on photoanode multilayers, which were coated with a ZnS or SiO2passivation, increased dramatic absorption in the visible light region as compared with other photoanodes and reduced rapid recombination proccesses in photovoltaic. As a result, the performance efficiency of TiO2/CdS/CdSe photoanode with SiO2passivation increased by 150% and 375% compared with TiO2/CdS/CdSe with ZnS passivation and TiO2/CdSe photoanode, respectively. For this reason, we note that the tandem multilayers can absorb more wavelengths in the visible light region to increase a large amount of excited electrons, which are transferred into the TiO2conduction band, and decrease number of electrons returned to the polysulfide electrolyte from QDs when a ZnS or SiO2passivation is consumed. Moreover, it is obvious that there was a far shift towards long waves in UV-Vis spectra and a sharp drop of intensity in photoluminescence spectra. In addition, the dynamic process in solar cells was carried out by electrochemical impedance spectra.

Effect of gallium ion content on thermal stability and reliability of YAG: Ce phosphor films for white LEDs

Y2.94(Al1−xGax)5O12:0.06Ce (x = 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) phosphors were prepared by conventional solid-state reaction. Phosphor films are prepared from the synthesized Y2.94(Al1−xGax)5O12:0.06Ce phosphors by a simple spin coating method. The influence of different content of Ga3+ doping on the photoluminescence (PL) spectra, thermal stability and reliability of prepared Y2.94(Al1−xGax)5O12:0.06Ce (x = 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) phosphor films were investigated. The emission peak of the Y2.94(Al1−xGax)5O12:0.06Ce (x = 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) phosphor films shifted from 545nm to 520nm with the Ga3+ content(i.e. the value of x) increasing from 0.05 to 0.3 excited at 460nm. The phosphor films have excellent thermal stability, and the intensities of PL spectra decrease by about 2%, 5%, 20% and 50% at 373K, 423K, 473K and 523K, respectively. The xenon lamp aging test show that the relative PL spectra intensity of the phosphor films decreases to 95.55%, 96.24%, 96.05%, 97.67%, 95.96% and 93.22% with the x value is 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3 after the xenon lamp aging test for 168h. The high temperature and high humidity test show that the relative PL spectra intensity of the phosphor films decreases to 94.36%, 95.6%, 95.26%, 96.87%, 95.28% and 93.1% with the x value is 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3 after the condition of 85℃/RH85% for 168h. The thermal cycling test show that the relative PL spectra intensity of the phosphor films decreases to 90.6%, 91.4%, 93.76%, 94.38%, 91.84% and 88.81% with the x value is 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3 after the condition of 120℃ for 1h and −40℃ for 1h by turns for eight times. So, it can be generalized that low level of Ga3+ doping can enhance the thermal stability and reliability of Y2.94(Al1−xGax)5O12:0.06Ce phosphor films.

Temperature sensing property of hollow-core photonic bandgap fiber filled with CdSe/ZnS quantum dots in an UV curing adhesive

Abstract A temperature sensor based on the hollow-core photonic bandgap fiber filled with the CdSe/ZnS QDs dissolved in an ultraviolet (UV) curing adhesive is reported. The sensor shows a linear variation of the photoluminescence (PL) peak wavelength for a temperature range from 40 °C to 140 °C, with a correlation factor of 0.99263 and a sensitivity of 0.05744 nm/°C. Although the peak intensity of emission spectrum increased exponentially with the temperature, a linear temperature-dependence result with a correlation factor of 0.99917 and a slope of 2.04 × 10 −3 °C −1 can be obtained with a self-reference spectral intensity method. The linear variation characteristics of the peak wavelength and the self-reference intensity of PL spectrum indicates the designed fiber temperature sensor is feasible in the practical application.

Study of polymer Graphene Quantum Dot nanocomposites

We report a synthesis of well dispersed Graphene Quantum Dot (GQD) nanocomposites in a host cellulose acetate (CA) polymer system. It was systematically characterized using X-ray diffraction (XRD), Scanning electron microscope (SEM), Transmission electron microscope (TEM), Atomic force microscope (AFM), Fourier transform infrared spectroscopy (FTIR) and Ultra-violet and Visible (UV–Vis), Photoluminescence (PL) techniques. Carboxylic and hydroxyl functional groups of GQD have chemically interacted with hydroxyl functional group of polymer network that leads to stabilization of the nanocomposite system. We observed that the amorphous to semi-crystalline phase disparity as a function of GQD loading which predominantly influenced the properties of nanocomposites. Decreased direct band gap of nanocomposites was analyzed by UV–Vis spectroscopic technique. Due to uniform dispersion and optimal loading of GQD in CA matrix an intense photoluminescence spectrum was observed. The existence of GQD occupied in the polymer system was examined by SEM, AFM and TEM microscopic techniques. It has been found that electrical conductivity of the composite was depended on temperature and similarly, decreased softness was related to the function of GQD loading. This investigation can be extendable for the devolvement of optical and electrical devices.

Concentration- and temperature-dependent photoluminescence of CsPbBr3 perovskite quantum dots

The concentration and temperature dependence of photoluminescence (PL) performance was investigated, which indicated that the main emission in CsPbBr3 perovskite quantum dots was related to the band-edge mechanism. As the concentration increased from 0.1 to 10.0mol/L at 293K, the center of emission band exhibited a regular redshift, as well as the peak intensity increased initially and then declined, which could be attributed to the self-absorption processes. Along with the variation of temperature (273–353K), peak wavelength, full width of half maximum (FWHM), and peak intensity of PL spectra presented a corresponding linear changes. In addition, the temperature reversibility revealed that CsPbBr3 QDs were reliable candidates for temperature sensor and optoelectronic devices.

Photoluminescence of silica monoliths prepared from cold sintering of nanometric aerosil precursors under high pressure

Blue photoluminescent silica monoliths were obtained by cold sintering of nanosized precursors under high pressure. The samples were prepared from hydrophobic and hydrophilic fumed silica AEROSIL® precursors which were placed inside a soft capsule of hBN and pressed at 7.7GPa. Practically no photoluminescence (PL) emission was observed for the nanometric powdered precursors while a relatively intense emission was measured for the sintered monoliths, which was dependent on the excitation wavelength (2.47–5.63eV). The emission was observed in the range between 2.0 and 3.5eV for all samples with the peak at ~2.7eV for excitation between 3.26–3.44eV. The blue band is probably related to the defects produced during the cold sintering process related to plastic deformation and internal stress of the monolith. The intensity of PL spectra of the monoliths obtained from the hydrophilic precursor (A200) was higher than the intensity of the spectra observed for the monoliths obtained from hydrophobic precursors (R974, R816 and R812) probably due to the presence of the carbon groups at the surface of the hydrophobic precursors, hindering the cold sintering process.

Investigation on optical and photoluminescence properties of organic semiconductor Al-Alq3 thin films for organic light-emitting diodes application

The optical constants, photoluminescence properties, and resistivity of Al-Alq3 thin films prepared by the thermal co-evaporation method on a silicon substrate are studied with various Al fractions. A variable angle spectroscopic ellipsometry is employed to determine the optical constants in the wavelength from 300 to 1200 nm at incidence angles of 65°, 70°, and 75°, respectively. Both the refractive indices and extinction coefficient apparently increase with increasing Al fractions. The intensity of photoluminescence spectra gradually increases with decreasing Al fractions due to intrinsic energy level transition of Alq3 organic semiconductor in the ultraviolet wave band. The resistivity decreases from 42.1 to 3.36 Ω·cm with increasing Al fraction from 40% to 70%, resulting in a larger emission intensity in photoluminescence spectra for the 40% Al fraction sample.