Photoluminescence Emission Spectroscopy Research Articles

Effects of composition and reduction conditions on persistent luminescence of SrAl2O4:Eu,Dy prepared via a solid-state reaction

SrAl2O4:Eu,Dy is a representative persistent luminescent phosphor that has been widely investigated. However, the mechanism of its long-lasting action has not been fully elucidated. With the aim of providing new insights into trapping in the phosphor by elucidating the relationship between trap creation and preparation conditions, SrAl2O4:Eu,Dy phosphors with different nominal Sr:Al compositions were prepared via a solid-state reaction and heating under different reducing conditions. The photoluminescence (PL) and persistent luminescence (PersL) emission and excitation spectroscopy of the phosphors, as well as their afterglow and thermoluminescence (TL) characteristics, were studied. SrxAl2O4:Eu2+,Dy3+ with x = 0.79–0.89 prepared via preheating in air and post-reduction showed the best afterglow properties. The PersL excitation spectra of these phosphors featured the same characteristic peaks, which were attributed to oxygen vacancies (electron traps) induced by Sr deficiencies. The TL measurements revealed that co-doping with Dy3+ ions increased the number of trapped electrons in pre-existing oxygen vacancies with trap depths of ∼0.53 eV and stabilized traps with depths of ∼0.61 eV via interactions with pre-existing oxygen vacancies that increase in number with Sr deficiency and preheating in air.

Alternate-Target Layer-By-Layer Pulsed Laser Deposition of Epitaxial BiVO4 Thin Films

Bismuth vanadate (BiVO4) has emerged as one of the highest performing metal oxide photoelectrodes for solar energy-to-fuels applications [1, 2]. This achievement has been largely attributed to the development of high-quality synthesis techniques. Specifically, epitaxial synthetic routes to producing lattice-matched, near single-crystalline quality BiVO4 with minimal extrinsic defects have been essential to understand the fundamental and PEC properties of BiVO4 that are inaccessible by conventional bulk synthesis techniques. In addition, epitaxial synthesis may also be employed as a strategy to further improve the PEC properties of BiVO4 through, for instance, altering the band structure and enhancing the carrier dynamics by strain engineering. Hence, the ability to produce high-quality single-phase epitaxial BiVO4 films is desirable.To date, molecular beam epitaxy (MBE), chemical vapor deposition (CVD), and pulsed laser deposition (PLD) [3] have been used to fabricate epitaxial BiVO4 thin films, with PLD having the advantage of relatively simple experimental setup and material versatility. However, an oft-noted drawback in conventional PLD using single oxide targets is off-stoichiometry in the deposited films; this is especially so for BiVO4 which requires a Bi-rich compound target to achieve a stoichiometric BiVO4 film [4]. This problem is also expected in general for multinary oxides composed of elements with very different ablation properties. To alleviate the limitations of conventional PLD, we employ for the first time alternate-target layer-by-layer PLD as a more elegant approach to produce high quality epitaxial BiVO4 films. Briefly, constituent oxide targets are alternately ablated by an excimer laser (λ= 248 nm) to build the desired film one unit cell thick at a time. Stoichiometry is controlled by the number of shots corresponding to a specified laser fluence for the constituent oxide target.To demonstrate the method, we deposited epitaxial BiVO4 films onto (001)-oriented yttrium-stabilized zirconia (YSZ) using 4N-pure Bi2O3 and V2O5 targets. Films grown are single phase BiVO4 as shown by x-ray diffraction. Out-of-plane diffraction peaks indexed to BiVO4(00l) suggests epitaxy of the film onto the substrate; reciprocal space maps of the asymmetric BiVO4(208) and YSZ(204) peaks further confirm the BiVO4(001) || YSZ(001) epitaxial relationship (top figure). Rocking curves of the BiVO4 (004) peak (FWHM ~ 0.015-0.041) indicate high crystalline perfection of the BiVO4 film, almost approaching that of the YSZ substrate (FWHM ~ 0.010). Thickness dependent-rocking curve studies reveal that BiVO4 films are strained to the substrate for film thicknesses under 22 nm; above this critical thickness, film relaxation ensues. In turn, the resulting optoelectronic properties of the BiVO4 film is dictated by its relaxation state. The optical band gap narrows with film relaxation as observed with spectroscopic ellipsometry. Moreover, steady-state photoluminescence emission spectroscopy reveals a sub-bandgap state (A 2, bottom figure) associated with strained BiVO4 films, on top of a state consistent with band-to-band recombination (B1 ). A higher energy sub-bandgap state (A 1, bottom figure) develops as the film relaxes. The implications of the relaxation state on the charge carrier dynamics and photoelectrochemical properties of BiVO4 will be discussed. Figure: (top) reciprocal space maps of the asymmetric BiVO4(208) and YSZ(204) peaks; (bottom) photoluminescence emission spectra of strained and relaxed BiVO4 films.

Immobilization of a [CoIIICoII(H2O)W11O39]7- Polyoxoanion for the Photocatalytic Oxygen Evolution Reaction.

The ongoing transition to renewable energy sources and the implementation of artificial photosynthetic setups call for an efficient and stable water oxidation catalyst (WOC). Here, we heterogenize a molecular all-inorganic [CoIIICoII(H2O)W11O39]7– ({CoIIICoIIW11}) Keggin-type polyoxometalate (POM) onto a model TiO2 surface, employing a 3-aminopropyltriethoxysilane (APTES) linker to form a novel heterogeneous photosystem for light-driven water oxidation. The {CoIIICoIIW11}-APTES-TiO2 hybrid is characterized using a set of spectroscopic and microscopic techniques to reveal the POM integrity and dispersion to elucidate the POM/APTES and APTES/TiO2 binding modes as well as to visualize the attachment of individual clusters. We conduct photocatalytic studies under heterogeneous and homogeneous conditions and show that {CoIIICoIIW11}-APTES-TiO2 performs as an active light-driven WOC, wherein {CoIIICoIIW11} acts as a stable co-catalyst for water oxidation. In contrast to the homogeneous WOC performance of this POM, the heterogenized photosystem yields a constant WOC rate for at least 10 h without any apparent deactivation, demonstrating that TiO2 not only stabilizes the POM but also acts as a photosensitizer. Complementary studies using photoluminescence (PL) emission spectroscopy elucidate the charge transfer mechanism and enhanced WOC activity. The {CoIIICoIIW11}-APTES-TiO2 photocatalyst serves as a prime example of a hybrid homogeneous–heterogeneous photosystem that combines the advantages of solid-state absorbers and well-defined molecular co-catalysts, which will be of interest to both scientific communities and applications in photoelectrocatalysis and CO2 reduction.

Coupling Ruthenium Bipyridyl and Cobalt Imidazolate Units in a Metal-Organic Framework for an Efficient Photosynthetic Overall Reaction in Diluted CO2.

Artificial photocatalytic CO2 reduction, using water as the reductant, is challenging mainly because it is difficult for multiple functional units to cooperate efficiently. Here, we show that the classic photosensitive and H2O-oxidizing ruthenium bipyridyl units and CO2-reducing cobalt imidazolate units can be incorporated into a metal-organic framework using a classic organic ligand, imidazo[4,5-f][1,10]phenanthroline. Under visible light without additional sacrificial agents and photosensitizers, the overall conversion of CO2 and H2O to CO and O2 was achieved by the multifunctional photocatalyst in the CH3CN/H2O mixed solvent with a high CO production rate of 11.2 μmol g-1 h-1 and CO selectivity of ca. 100%. Thanks to its ultramicroporous structure with moderately strong CO2 adsorption ability, the photocatalyst also exhibited high performances with CO/CH4 production rates of 5.15/0.62 and 4.26/0.20 μmol g-1 h-1 in the gas phase with pure and even diluted CO2, respectively. Photoluminescence emission spectroscopy and photoelectrochemical tests confirmed that the photosensitive and catalytic units cooperated well to give suitable photocatalytic redox potentials and fast electron-hole separation.

An Efficient Inclusion Complex Based Fluorescent Sensor for Mercury (II) and its Application in Live-Cell Imaging.

The formation of an inclusion complex between hydroxypropyl-β-cyclodextrin (H-CD) and 4-acetylphenyl-4-(((6-chlorobenzo[d]thiazol-2-yl)-imino)-methyl)-benzoate (L) was investigated by FT-IR, 1H-NMR, X-ray diffraction (XRD), FT-Raman, scanning electron microscope (SEM) techniques in the solid-state, absorption and emission spectroscopy in the liquid state and the virtual state as molecular docking technique. The binding properties of the inclusion complex (H-CD: L) with cations in deionized water was observed via absorbance and photoluminescence (PL) emission spectroscopy. The fluorescence probe (H-CD: L) inclusion complex (IC) was examined for several heavy metal cations, and identified that the PL emission wavelength of the complex displayed a continuous rise in the fluorescence intensity for Hg2+. A linearity range of 1 × 10-8 - 11 × 10-8M and limit of detection value of 2.71 × 10-10M was found to be achieved for the detection of Hg2+. This outcome proves that the inclusion complex H-CD: L would be a promising material for the development a solid-state fluorescence probe for detecting Hg2+. It also shows application in real sample analysis and cell imaging.

Effects of the polarization field on optical transitions and selection rules in Er doped GaN

Effects of the polarization field on the Er3+ intra-4f shell transitions in GaN have been investigated via comparison of photoluminescence emission spectroscopy studies conducted on Er:GaN and Er:YAG. The dominant optical transitions were compared and analyzed. It was observed that the dominant optical transitions in Er:GaN/Er:YAG are between the Stark levels of the same/different irreducible representations. The unique selection rules in Er:GaN are a consequence of the presence of a net local polarization field acting on Er due to the wurtzite crystal structure of GaN. The results provide useful insights into understanding of the dominant optical transitions and the most probable emission lines to be utilized to achieve lasing in Er:GaN.

Construction of new recoverable Ag-Fe3O4@Ca–Al LDH nanohybrids for visible light degradation of piroxicam

Herein, for the first time, a hybrid material is used as an efficient photocatalyst to degrade piroxicam under visible light. By the use of Ag-Fe3O4@Ca–Al LDH hybrid (AFL hybrid), piroxicam (PX) solution was 95% degraded to CO2 and H2O in 150 min. The kinetic study showed that the degradation reaction of PX over photocatalyst adjusts well to a pseudo-first-order reaction kinetic. Optimizing the effective factors on reaction rates such as %Ag, PX solution concentrations, Na2SO4 amount, and catalyst dosage increased the rate constant to 0.03 min−1. The optical and electrical characteristics of AFL hybrid were studied through solid-state UV–vis diffuse absorption, photoluminescence emission (PL) spectroscopy, and photocurrent response, which predicted the high catalytic performance of the hybrid. The active radical capturing tests exhibited that O2– playing a major role in PX photodegradation by the assistant of Na2SO4. Also, the hybrid recovered easily by an external magnetic field.

Exceptional removal of methylene blue and p-aminophenol dye over novel TiO2/RGO nanocomposites by tandem adsorption-photocatalytic processes

Herein, a novel RGO/TiO2 nanocomposites were successfully synthesized via facile mechanical method for photocatalytic removal of methylene blue dye (MB) and p-aminophenol. The as-synthesized composites were characterized by Transmission Electron Microscopy (TEM), X-ray powder diffraction (XRD) and N2-adsorption–desorption isotherms, Photoluminescence emission spectroscopy (PL) and UV–Vis spectroscopy techniques. The photocatalytic performance of the as-synthesized nanocomposites was explored through the degradation of MB in the presence of UV and natural sunlight. The sensitization of TiO2 with RGO exhibited efficient separation of the photoinduced charge carriers, slightly shifted the optical absorption edge towards the visible region and enhanced the photocatalytic activity under UV and natural sunlight irradiation. The dye photodegradation process follows a pseudo-first-order kinetics with respect to the Langmuir-Hinshelwood reaction mechanism. The most probable photocatalytic reaction mechanism has been proposed according to the obtained experimental results of this work.

Local Surface Plasmonic Resonance, Surface-Enhanced Raman Scattering, Photoluminescence, and Photocatalytic Activity of Hydrothermal Titanate Nanotubes Coated with Ag Nanoparticles

In this work, we successfully fabricated homogeneous hydrothermal titanate nanotubes (TNTs) coated with Ag nanoparticles (NPs) and elucidated the role of Ag NPs on local surface plasmonic resonance, surface-enhanced Raman scattering, and the enhanced photocatalytic activity of TNT/Ag nanocomposite. The results showed that the photodegradation process reached equilibrium in just ~5 min for the TNT/Ag nanocomposite, which was much shorter than that of the TNT sample (~90 min). TEM micrographs showed that Ag NPs were well dispersed on the walls of the nanotubes. XRD patterns and Raman spectra indicated that the TNTs were in the monoclinic structure of H2Ti3O7. Furthermore, Raman active modes of the TNTs were significantly enhanced in the TNT/Ag sample, which was attributed to surface-enhanced Raman spectroscopy. The enhanced photocatalytic activity of the TNT/Ag sample was explained by UV-vis diffuse reflectance spectroscopy and photoluminescence emission spectroscopy, which showed local surface plasmonic resonance-induced visible light absorption enhancement and effective charge separation, respectively.

Influence of the concentration of chenodeoxycholic acid on the performance of the N719 dye

The influence of the Chenodeoxycholic acid (CDCA) at different concentrations on the spectroscopic and photovoltaic performances of the N719 dye was determined. Absorption analyses revealed the excellent capacity of the CDCA in stabilizing the N719 dye. The N719 dye exhibited hydroxyl and carboxylic functional groups that were accountable for the strong interactions and fast transport of electrons to the TiO2 surface. The photoluminescence emission spectroscopy of the CDCA-incorporated dye exhibited the feasibility of a large photocurrent generation. The interaction mechanism of CDCA within the N719 dye influenced the efficiency of the fabricated cell because the high photoconversion efficiency of 4.07% was recorded for 0 mM CDCA. This finding was because CDCA decreased the electrolyte contact with the N719 dye, resulting in charge accumulation in the electrolyte and decreased electron density in the N719 dye. Present findings are beneficial for the development of efficient dye-based DSSCs.

Biosynthesis of rod shaped Gd2O3 on g-C3N4 as nanocomposite for visible light mediated photocatalytic degradation of pollutants and RSM optimization

To investigate visible light-driven photocatalytic activity, novel heterogeneous catalysts were constructed employing graphitic carbon nitride (g-C3N4) and gadolinium oxide (Gd2O3). Each catalyst was prepared separately. To begin, melamine was used to synthesize g-C3N4. Gd2O3 was prepared via green synthesis by utilizing Cocos nucifera coir extract as a capping agent. Then the prepared g-C3N4 and Gd2O3 were combined in order to form Gd2O3/g-C3N4 nanocomposite. The sole aim of the fabrication of this nanocomposite is to degrade organic pollutants such as amaranth (AM) and congo red (CR) dye, utilizing visible light. The Gd2O3/g-C3N4 nanocomposite was found to be an efficient catalyst in the degradation of AM and CR dye. The prepared nanocomposite was characterized utilizing various techniques like X-ray diffraction, Fourier transform-infra red (FT-IR), UV–visible diffuse reflectance spectroscopy (UV–Vis DRS) and Photoluminescence emission (PL) spectroscopy. The surface area and the surface charge were examined with the aid of BET analysis and Zeta potential respectively. Scanning electron microscope (SEM) and a Transmission electron microscope (TEM) were used to investigate the synthesized nanocomposite's morphology. In contrast with g-C3N4, Gd2O3 and Gd2O3/g-C3N4 have a larger surface area. The Gd2O3/g-C3N4 nanocomposite's PL emission spectra confirmed the lower electron-hole (e-_h+) pair recombination rate. The Gd2O3/g-C3N4 nanocomposite has proved to be an outstanding catalyst with a degradation efficiency of 95% towards CR. Furthermore, the experiments were optimized using Response surface methodology (RSM). These findings revealed that the dye concentration, pH, and catalyst dosage are important parameters in the photocatalytic degradation process. The high correlation co-efficient for the second order polynomial model demonstrated that the data predicted using RSM was in agreement with the experimental results. This work adds to the understanding of g-C3N4-based rare earth metal oxide nano-photocatalysts for efficient organic pollutant degradation.

Enhancing the photocatalytic activity of Ag-TiO2/SiO2 and its potential application in water treatment

Ag-doped TiO2/SiO2 with visible light response was prepared by a simple sol-gel method using titanium w-butoxide (TNB), tetraethoxysilane (TEOS) as precursors, and silver nitrate (AgNO3). The synthesized Ag-TiO2/SiO2 were characterized by SEM, XRD, PL (photoluminescence) emission and UV-Vis absorption spectroscopy. Their photocatalytic activities were evaluated by treating aqueous solutions of phenol under simulated visible light illumination. The role of silver doped was investigated in the range 1% – 5% (molar ratio), resulting in the best bandgap value of 2.93 eV for Ag(3%)-TiO2/SiO2 compared to 3,18 eV for the un-doped TiO2/SiO2. Consequently, the best phenol treating yield – about 97% after 4 hours – was obtained using Ag(3%)-TiO2/SiO2. So the synthesized Ag(3%)-TiO2/SiO2 might serve as a potential photocatalyst for water treatment using visible lights.

Yellow Emissive Tris(8-hydroxyquinoline) Aluminum by the Incorporation of ZnO Quantum Dots for OLED Applications.

Tris(8-hydroxyquinoline) aluminum complexes are of significant interest because of their remarkable optical and electrical properties, both as an emissive layer and electron injection layer. They emit light in the blue and green ranges of the visible spectrum, so for white organic light emitting diodes (OLEDs), yellow emission is required as well. In this study, we propose the use of zinc oxide quantum dots to tune the emission color of the complex while maintaining its luminous efficiency. Hence, tris(8-hydroxyquinoline) aluminum-zinc oxide nanohybrids with different zinc oxide quantum dots concentrations (10, 20, or 30 wt.%) were synthesized. The structural properties were characterized using powder X-ray diffraction analysis, while the composition and optical characteristics were characterized by Fourier transform infrared spectroscopy, UV-visible absorption spectroscopy, and photoluminescence emission spectroscopy. The results show that increased levels of zinc oxide quantum dots lead to a decrease in crystallinity, double hump emission and a slight red shift in emission peaks. Also, at 20 and 30 wt.% of zinc oxide quantum dots concentrations, yellow emission was observed.

A Highly Efficient Eu2+ Excited Phosphor with Luminescence Tunable in Visible Range and Its Applications for Plant Growth

AbstractA series of RbxK2−xCaPO4F:Eu2+ phosphors are synthesized using a high‐temperature solid‐phase method. An increase in the Rb+ concentration leads to the Eu2+‐excited phosphor emission spectra being shifted from red to cyan. Interestingly, the excitation spectrum does not exhibit any variations, which indicates the possibility of mixing the red (Rb0.2K1.8CaPO4F:Eu2+) and cyan (Rb2CaPO4F:Eu2+) phosphors for plant growth. This luminescence tuning is attributed to the substitution of K+ with Rb+, which produces an inferior crystal‐field splitting that increases the energy at the lowest 5d level, and enhances the rigidity of the crystal structure, which results in a gradual decrease in the Stokes shift and a consequent blue shift in the emission spectrum. Time‐resolved photoluminescence emission spectroscopy further confirms the occurrence of broadband emission owing to the occupation of multiple sites by Eu2+. Light‐emitting devices appropriate for plant growth are fabricated by mixing the two phosphors with a 380‐nm UV chip, and a light‐conversion film is prepared using the red phosphor and PDMS glue. The Chlorella‐based plant growth experiment reveals that the growth rate of Chlorella is 12.2% higher than that of the blank group, indicating the favorable effect of the light‐conversion film on plant growth.

Pegylated Eu-enabled submicron alumina spheres as potential theranostics agent RD cell line as model.

ObjectivesThis study is aimed to synthesis and evaluate PEGylated Eu enabled spherical alumina submicron particles (s-Al2O3:Eu) for potential theranostic applications.MethodsThis study is bisected into two parts, a) synthesis of PEGylated Eu enabled spherical alumina submicron particles (s-Al2O3:Eu), and b) characterization of the synthesized particles to determine their efficacy for potential theranostic applications.The synthesis of the particles involved the following steps. In the first step, s-Al2O3:Eu is synthesized using solvothermal synthesis. In the next step, the particles undergo post synthesis water–ethanol treatment and calcination. The surface of the synthesized s-Al2O3:Eu particles is then coated by PEG to increase its biocompatibility.Once the particles are prepared, they are characterized using different techniques. The microstructure, composition and structure of the particles is characterized using SEM, EDX and XRD techniques. The detection of the functional groups is done using FTIR analysis. The photoluminescence emission spectrum of s-Al2O3:Eu is studied using Photoluminescence spectroscopy. And, finally, the biocompatibility is studied using MTT assay on RD cell lines.ResultsThe microstructure analysis, from the micrographs obtained from SEM, shows that the spherical alumina particles have a submicron size with narrow size distribution. The compositional analysis, as per EDX, confirms the presence of Oxygen, Aluminum and Europium in the particles. While, XRD analysis of s-Al2O3:Eu confirms the formation of alpha alumina phase after calcination at 700 °C. Emission peaks, obtained by Photoluminescence emission spectroscopy, show that the optimum emission intensities correspond to the transition from 5D0 to 7Fj orbital of Eu+3. FTIR analysis confirms the successful coating of PEG. Finally, a cell viability of more than 86% is observed when the biocompatibility of the particles is studied, using MTT assay on RD cell lines.Conclusionss-Al2O3:Eu with narrow distribution are successfully synthesized. Structural and functional characterizations support the suitability of s-Al2O3:Eu as potential theranostic agent.

One-Step Microwave-Assisted Synthesis and Visible-Light Photocatalytic Activity Enhancement of BiOBr/RGO Nanocomposites for Degradation of Methylene Blue.

In this study, bismuth oxybromide/reduced graphene oxide (BiOBr/RGO), i.e. BiOBr-G nanocomposites, were synthesized using a one-step microwave-assisted method. The structure of the synthesized nanocomposites was characterized using Raman spectroscopy, X-ray diffractometry (XRD), photoluminescence (PL) emission spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), and ultraviolet-visible diffuse reflection spectroscopy (DRS). In addition, the ability of the nanocomposite to degrade methylene blue (MB) under visible light irradiation was investigated. The synthesized nanocomposite achieved an MB degradation rate of above 96% within 75 min of continuous visible light irradiation. In addition, the synthesized BiOBr-G nanocomposite exhibited significantly enhanced photocatalytic activity for the degradation of MB. Furthermore, the results revealed that the separation of the photogenerated electron–hole pairs in the BiOBr-G nanocomposite enhanced the ability of the nanocomposite to absorb visible light, thus improving the photocatalytic properties of the nanocomposites. Lastly, the MB photo-degradation mechanism of BiOBr-G was investigated, and the results revealed that the BiOBr-G nanocomposites exhibited good photocatalytic activity.

Insight role of TiO2 to improve the photocatalytic performance of WO3 nanostructures for the efficient degradation of ciprofloxacin

Abstract The current research work is to investigate the photocatalytic efficiency and degradation of ciprofloxacin using WO3/TiO2 nanoparticles under visible light irradiation. The nanoparticles of tungsten trioxide (WO3) and its composite with titanium dioxide (TiO2) i.e. WO3/TiO2 was prepared by hydrothermal method. Four basic characterizations were performed to study the prepared sample materials. To study the morphology of the prepared samples, scanning electron microscopy (SEM) was used. The results of SEM clearly showed that tungsten trioxide (WO3) has Rectangular shaped structure. The average size of the pure Tungsten trioxide nanoparticles was about 40–540 nm. The composite of WO3/TiO2 has spherical structure. The reason behind that was the addition of TiO2 in WO3 changes the morphology of pure WO3, and transformed the rectangular structure to a spherical structure. The presence of TiO2 changes the position and orientation of the nanorods in all possible directions. For the detailed analysis of the functional groups present in these samples, band gap, and optical properties of these samples, Fourier transform infrared spectroscopy (FTIR), ultraviolet visible (UV–VIS) spectroscopy and Photoluminescence (PL) emission spectroscopy was used. UV–Vis spectroscopy results showed that the bandgaps of prepared catalysts vary within the range of 2.76 – 2.5 eV. This decrease in bandgap is directly related with the concentration ratio of TiO2 in WO3. The maximum excitation wavelength observed at 440 nm. The maximum degradation efficiency was at 2% of WO3/TiO2 composite catalyst due to unique morphological structure and increase rate of photo absorption.

Role of PVA capping on photophysical properties of chemically prepared CdS nanomaterials: Insights on energy transfer mechanisms in the capped system

Radiative and nonradiative relaxation mechanisms of carriers in CdS nanomaterials capped by polyvinyl alcohol (PVA) and energy transfer processes between PVA and intrinsic vacancies or defects in CdS have been investigated in the present work. Highly luminescent PVA encapsulated CdS nanomaterials have been synthesized via chemical co-precipitation method with varying PVA concentration. XRD shows a hexagonal (wurtzite) structure of nanomaterials with crystallite sizes ranging from 6 nm to 10 nm. Surface morphology shows spherical shapes of agglomerated nanoclusters; additive makes them more compact and further agglomerated within the nanomaterials. Blue shifting in absorption band of as-synthesized nanomaterial from that of bulk reveals the effect of quantum confinement. Urbach energy is increased; accordingly, the band gap of nanomaterials is also decreased with addition of PVA in CdS. Photoluminescence emission spectroscopy indicates that both excitonic and defect emission intensities are enhanced due to the suppression of nonradiative recombination. The role of interaction between PVA and CdS in controlling emission colours and intensity has been explored. Chromaticity analysis reveals tunability in emission colours with high colour purity. Luminescence quantum efficiency and electroluminescence efficiency have also been assessed. Observed enhancement in optical properties makes the capped CdS nanomaterials promising for future generation QD LED applications.

Effects of X-ray irradiation on the structural and optical properties of microcrystalline Alq3 powder and its potential dosimetry application

Tris-(8-hydroxyquinoline) aluminum (Alq3) is a well-known organometallic compound due to its numerous applications in electronic devices including organic light-emitting diodes, photodiodes, and optoelectronics. It has unique optical properties; however, the effect of ionizing radiation on its properties has not been investigated to date. In this study, Alq3 microrods were pressed into small pellets, annealed at 150 °C for 1 h and then exposed to X-ray radiation at different doses in the range of 5–20 Gy. Subsequently, their structural and optical properties were analyzed by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and photoluminescence (PL) emission spectroscopy. XRD results showed a slight shift in the positions of the Alq3 peaks, with no significant change in the crystallinity or phase of Alq3, whereas the intensity of the Raman and FTIR peaks of these pellets systematically decreased upon irradiation. The intensity of the PL band of Alq3 at 510 nm initially increased to about three times higher than the unirradiated PL signal under 10 Gy irradiation and then started to decrease. The observed decreases in the intensities of the Raman and FTIR peaks are attributed to the slow/gentle degradation of Alq3, particularly to the breakage of its C–H, C–O, and Al–O bonds. In addition, the linear dose response of Raman and FTIR signals present a nearly excellent dose dependence with a minimal percentage error of 1% and 4%, respectively. These results might serve as a basis for the further investigation of Alq3 microrods as a radiation dosimeter. In particular, the observed systematic modifications in the optical properties of Alq3 and the resulting excellent linear response curves of irradiation doses verses signal intensities are quite encouraging.

Phosphate-Templated Encapsulation of a {CoII 4 O4 } Cubane in Germanotungstates as Carbon-Free Homogeneous Water Oxidation Photocatalysts.

The ever‐growing interest in sustainable energy sources leads to a search for an efficient, stable, and inexpensive homogeneous water oxidation catalyst (WOC). Herein, the PO4 3− templated synthesis of three abundant‐metal‐based germanotungstate (GT) clusters Na15[Ge4PCo4(H2O)2W24O94] ⋅ 38H2O (Co4), Na2.5K17.5[Ge3PCo9(OH)5(H2O)4W30O115] ⋅ 45H2O (Co9), Na6K16[Ge4P4Co20(OH)14(H2O)18W36O150] ⋅ 61H2O (Co20) with non‐, quasi‐, or full cubane motifs structurally strongly reminiscent of the naturally occurring {Mn4Ca} oxygen evolving complex (OEC) in photosystem II was achieved. Under the conditions tested, all three GT‐scaffolds were active molecular WOCs, with Co9 and Co20 outperforming the well‐known Na10[Co4(H2O)2(PW9O34)2] {Co4P2W18} by a factor of 2 as shown by a direct comparison of their turnover numbers (TONs). With TONs up to 159.9 and a turnover frequency of 0.608 s−1 Co9 currently represents the fastest Co‐GT‐based WOC, and photoluminescence emission spectroscopy provided insights into its photocatalytic WOC mechanism. Cyclic voltammetry, dynamic light scattering, UV/Vis and IR spectroscopy showed recyclability and integrity of the catalysts under the applied conditions. The experimental results were supported by computational studies, which highlighted that the facilitated oxidation of Co9 was due to the higher energy of its highest occupied molecular orbital electrons as compared to Co4.