UV Vis Absorption Edge Research Articles

Optical properties and luminescence behavior of Tb3+-Doped SiO2–Al2O3–BaO–BaF2 oxyfluoride glasses and glass ceramics

In this study, oxyfluoride glasses with chemical composition of 45SiO2–15Al2O3–10BaO–30BaF2-xTbF3 (x = 0.2, 0.4 and 0.6 (mole ratios)) were prepared through the conventional melt-quenching method. Raman and FTIR spectra as well as molar volume calculations proved the creation of more non-bridging oxygens (NBOs) in presence of more TbF3 content. Accordingly, absorption edge in UV–Vis spectra showed a slight red-shift to longer wavelengths. The glass with 0.4 mol ratios of TbF3, exhibited the highest photoluminescence emission and its green-to-blue intensity ratio was 0.66. Therefore, this sample was chosen and heat treated at 630, 650 and 675 °C to prepare glass ceramic samples. For the sample heat treated at 650 °C, photoluminescence intensity increased and green-to-blue intensity ratio reached 0.69. Also, lifetimes of green and blue emissions increased from 3.35 ms to 3.67 ms and from 2.95 ms to 3.10 ms, respectively, when the base glass heat treated at 650 °C. Formation of BaF2 nanocrystals in glass ceramics moved the UV–Vis absorption edge to longer wavelengths significantly. Increment of the weak and dangling bonds in crystallized samples reduced Fermi energy, indirect and direct optical band gap energies from 3.792 eV to 3.301 eV, from 3.522 eV to 3.093 eV and from 4.095 eV to 3.582 eV respectively, which led to higher semiconducting behaviors.

Studying the structural, optical, and electrical characteristics of Zn2SnO4 films using a direct current magnetron sputtering method

In this study, the characteristics of ZTO films are examined by varying the substrate temperature at an Ar ambient pressure of 3 × 10−3 Torr. The elemental content of Zn, Sn, and O in the generated Zn2SnO4 films was confirmed using X-ray dispersive and X-ray photoelectron spectroscopy. The result reveals that the Zn/Sn ratio for the film formed at 300 °C reaches 2. The (222) and (311) lattice planes validated the cubic inverse spinel structure of ZTO films in the X-ray diffraction investigation. Atomic force microscopy was used to measure surface roughness, and the RMS rose in a range of 1.34–4.79 nm as the substrate temperature increased. Field-emission scanning electron microscopy revealed that the average crystal grain size grew in the region of 60–95 nm as the substrate temperature increased. The UV–vis absorption edge shift validates the Burstein-Moss shift rule, with a bandgap of ZTO-300 achieving the greatest value of 3.75 eV, corresponding to the largest carrier concentration. Electrical characteristics were investigated using Hall measurements. Film conductivity was primarily determined by the electron concentration or the presence of oxygen vacancies. The lowest resistivity measured was 5.4 × 10−3 Ω cm, which corresponded to an electron concentration of 8.57 × 1019 cm−3. The current-voltage characteristics of the ZTO/p-Si junction proved its rectifiable quality. Because of the low resistivity of the ZTO-300 sample, the ZTO-300/p-Si heterojunction has the largest photocurrent (4.72 10−3 A), making it suitable for use in optoelectronic devices.

Microemulsion synthesis of Ga and Sr doped BiFeO3 nanoparticles and evaluation of their ferroelectric, optical, dielectric and photocatalytic properties

A series of Ga and Sr doped bismuth ferrite (BiFeO₃) was synthesized using a facile microemulsion technique and characterized using XRD, SEM, Raman, PL and UV–vis techniques. The XRD and Raman study revealed the rhombohedral phase of Bi1-xSrxFe1-xGayO3 with R3‾c space group. The average crystalline size was in range of 28–42 nm. From P-E loop, the saturation polarization (Ps), coercivity (Hc) and remanence (Pr) were determined and value of Pr and Ps increased with increasing dopant contents. Furthermore, there was a decline in dielectric loss with increased frequency and dopant content. The PL revealed that the highly substituted material had lower re-combination rate and higher charge (e−-h+) separation, which was finally responsible for its enhanced photo-catalytic activity. For Ga and Sr doped BiFeO₃, UV–Vis absorption edge exhibited substantial red shift thus reducing bandgap from 1.91 to 1.19 eV for highest doped composition. Finally, the photocatalytic activity of the material was investigated using methyl orange (MO) as model contaminant. Bi1-xSrxFe1-xGayO3 exhibited much better photocatalytic efficiency and degraded 87% dye in comparison to pristine BiFeO3 (66%) within 70 min under solar light. Also, stability of samples was demonstrated through re-cycling experiment. Bi1-xSrxFe1-xGayO3 had higher stability and reusability compared to BiFeO₃. Based on these findings, Bi1−xSrxFe1−yGayO3 material may find use in high frequency devices and photo-catalytic applications for treatment of industrial wastes due to its promising dielectric and photo-catalytic outcomes.

Incorporation of N in p-type Zn-N-doped SnO2 films by varying N2 content in sputtering gas mixture

This study investigates a variation of the N2 content in the mixed sputtering gas effects on the optical, electrical, and structural properties of p-type Zn-N-doped SnO2 films. The incorporation of N into the tin oxide lattice of the synthesized films was confirmed by energy-dispersive X-ray spectroscopy, X-ray diffraction (XRD) analysis, ultraviolet–visible (UV–vis) spectroscopy, and Hall measurements. Further, atomic force microscopy, field-emission scanning electron microscopy, and current-voltage characteristics confirmed the substitution of O by N in the SnO2 lattice. The sufficiently large N3−–O2− substitution in the SnO2 lattice was confirmed by a (200) cubic plane in the XRD pattern. N3−–O2− substitution was also ascertained by the redshift of the UV–vis absorption edge. The crystallinity increased significantly with an increase in N3−–O2− substitution in the SnO2 lattice, including an increase in the crystal grain size and a decrease in surface roughness. The optimum N3−–O2− substitution for the film synthesized using 80% N2 in the mixed sputtering gas resulted in the best crystal quality. This film showed the highest hole mobility and the greatest increase in the photocurrent of the film/n-Si heterojunction. The excess N-substituted O content in the tin oxide lattice degraded the crystal quality. Therefore, the optimally synthesized film is more suitable for optoelectronic devices.

Structural evolution and ferroelectric properties of relaxor ferroelectric single crystal Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 under high pressure

Relaxor ferroelectric crystals of lead magnesium niobate–lead titanate (PMN-xPT) have attracted great attention due to their extraordinary dielectric, piezoelectric, and electromechanical properties. PMN-xPT shows different relaxor behavior and structural phase transitions in a wide temperature and chemical component range. Here, we studied spectroscopy and ferroelectricity of PMN-0.28PT under high pressure. The appearance of a new Raman band and the sudden redshift of UV-vis absorption edge imply a structural phase transition at about 8 GPa. More importantly, the ferroelectricity of the sample is suppressed above a pressure of 5 GPa, and there is no ferroelectricity under further compression. We suggest that the disappearance of ferroelectricity may be related to the polar nanoregions being suppressed by pressure. Our observations of ferroelectricity disappearance above 5 GPa indicate the B-site cation rearrangement in the several nanometers region.

Ferroelectric polarization-enhanced photodegradation performance for dyes in BaTiO3/AgAlO2 heterostructure

Introducing an internal electric field into photocatalysts is an efficient strategy to inhibiting the charge carrier recombination which is the obstacle to the photocatalytic technology. Herein, we propose to construct BaTiO3/AgAlO2 heterostructure with improved photocatalytic performance through a polarization effect. The ferroelectric BaTiO3 particles with nanocube morphology are distributed over ellipsoid-like AgAlO2. The UV–vis absorption edges extend from 415 to 545 nm owing to the energy band overlap. The ultrasound-assisted photocatalysis efficiency of methyl blue under BaTiO3/AgAlO2 is increased by 22 %. Photoelectrochemical results indicate that the separation efficiency of photoinduced carriers is enhanced by the polarization effect. Moreover, the photocurrent of the BaTiO3/AgAlO2 after polarization is increased by 1.6 times of that before polarization. Piezoelectric force microscope shows that the phase angle has a great change, confirming the polarization switching process. The butterfly-shaped displacement-voltage hysteresis loop confirms the local piezoelectric response originated from BaTiO3.

Ce and Fe doped LaNiO3 synthesized by micro-emulsion route: Effect of doping on visible light absorption for photocatalytic application

A series of La1−xCexNi1−yFeyO3 (x, y = 0.00–0.25) NPs was fabricated via micro-emulsion route and effect of doping was investigated on the basis of optical, photocatalytic and structural properties. The as-synthesized NPs were characterized via XRD, Raman analysis, SEM and UV–visible techniques. The XRD results confirmed the rhombohedral perovskite phase particles with particles of 60–80 nm range. UV–vis absorption edge showed significant red shift thereby tuning the band gap from 2.77 to 2.64 eV. The photocatalytic effectiveness of LaNiO3 and La0.80Ce0.20Ni0.80Fe0.20O3 catalysts was performed by degrading Congo red (CR) dye under visible light exposure. Substituted catalyst exhibited superior photodegradation by showing 97% degradation in comparison to pristine LaNiO3 (63% only) in 120 min. Degradation of CR followed the pseudo fist order kinetics. In addition, the catalyst dose effect, dye concentration and pH variation was studied for Cr dye degradation. Enhanced photocatalytic activity and narrow bandgap of Ce and Fe doped LaNiO3 introduce such materials as efficient visible active photocatalysts to be utilized in dye removal application from waste water and in photovoltaic applications, respectively.

Silver nanoparticles-supported graphitic-like carbon nitride for the electrochemical sensing of nitrobenzene and its derivatives

Nitrobenzene (NB) is toxic even at low concentrations and hence its contamination in the environment is a pervasive concern. The electrochemical techniques have emerged as rosy method to sense and degrade NB and graphitic carbon nitride (g-C3N4) catalysts are found to be promising for this. In this study, silver nanoparticles (AgNPs)-decorated n-[3-(trimethoxysilyl)propyl]ethylenediamine (EDAS)-modified graphitic carbon nitride nanocomposites [EDAS/(g-C3N4-Ag)NC] having various silver concentrations are prepared through a facile method and applied for the electrochemical sensing of NB derivatives. UV–vis absorption edge at 430 nm together with a broad surface plasmon resonance (SPR) peak at 450 nm indicates the existence of AgNPs on the g-C3N4 nanosheets. FTIR spectra endorse the presence of g-C3N4 nanosheets in the composite. The presence of Ag in EDAS/(g-C3N4-Ag)NC is confirmed by transmission electron microscopy, energy dispersive X-ray analysis, and cyclic voltammetry (CV). The nanocomposite prepared with 2 mM Ag+ shows superb electrocatalytic activity toward the reduction of nitrobenzene and its derivatives. Sensitivity of the modified electrode and limit of detection (LOD) for NB assessed by square wave voltammetry are found to be 0.594 A M−1 cm−2 and 2 µM, respectively, in the linear range of 5–50 µM.

Investigation on the growth, structural, optical, thermal and third-order nonlinear optical (NLO) properties of 2,3-dimethyl-N-[(E)-2,4,5-trimethoxybenzylidene] aniline (DTA) organic single crystal

Good-quality organic nonlinear single crystal of 2,3-dimethyl-N-[(E)-2,4,5-trimethoxy benzylidene] aniline (DTA) was synthesized and successfully grown at room temperature by adapting slow evaporation technique using mixed solvent of acetone and methanol. The crystal structure was experimentally confirmed by single-crystal X-ray diffraction, where the DTA crystals crystallize in the centric space group (P $$\overline{1}$$ ) with triclinic crystal system. The surface morphology of DTA was examined by the Field Emission Scanning Electron Microscope (FE-SEM) technique. The presence of various modes of functional groups of the title crystal was analyzed by Fourier-Transform Infra-Red (FT-IR) spectra. Ultraviolet–Visible-Near Infrared (UV–Vis–NIR) spectrum showed high optical transparency of ~ 88% in the Vis and NIR region with a UV–Vis absorption edge of 390 nm. The result of photoluminescence studies suggests that the DTA crystal can be used as source material to exhibit green emission light. From thermogravimetric-differential scanning calorimetry (TG-DSC) analysis, the melting point of the grown crystal was found to be 111 °C. The standard Z-Scan technique was employed to evaluate the third-order nonlinear optical properties of the DTA crystal. The obtained third-order nonlinear parameters were compared with few of the already reported NLO crystals. All these findings indicate that the title crystal may be an attractive material for nonlinear optical device applications.

Facile construction of silver-based solid solution heterophase for efficient visible-light-driven photocatalytic degradation of tetracycline

Silver-based solid solutions as photocatalysts exhibit potential applications owing to the unique crystal and electronic structures, but single phase usually encounters low separation efficiency of photoinduced carriers and poor visible-light absorption, causing low photocatalytic activity. Thus, it is meaningful to design novel solid solution photocatalysts to solve these issues. In this work, mixed-phase heterostructures of α/β-AgAl0.4Ga0.6O2 solid solution are in-situ obtained by phase transformation of β-AgAl0.4Ga0.6O2 pre-prepared by a simple solid-state reaction. The study of phase and microstructure demonstrates that the mixed-phase heterostructure includes two phases of α and β-AgAl0.4Ga0.6O2 with high crystallinity. Platelet-like α phase is combined with polyhedral β phase, yielding close contract and large interfaces owing to in-situ preparation by phase transformation. The UV–vis absorption edge of mixed-phase heterostructure can be controlled from 500 to 575 nm through the energy band overlap of two phases. The mixed-phase heterostructure exhibits the improved visible-light photocatalytic performance. The degradation rate of tetracycline reaches 87% in comparison to the 31% for α phase and the 69% for β phase. This is mainly attributed to the enhanced carrier separation and migration efficiency verified by photoelectrochemical investigation. Especially, the photocurrent value of mixed-phase heterostructure is 5 and 7 times higher than those of β phase and α phase, respectively. Considering the practical applications, the effects of tetracycline concentration, photocatalyst dosage, pH, and coexistence anions on the photocatalysis performance were investigated for tetracycline degradation. In addition, the recyclability, oxidization species, possible photocatalytic mechanisms were also studied and proposed. This work might promote the prospective research of semiconductor photocatalysis in wastewater purification.

Hydrothermal synthesis of star-shaped Bi5O7Br catalysts with strong visible light catalytic performance

Micron star-shaped Bi5O7Br catalysts were synthesized, with Bi(NO3)3·5H2O and cetyltrimethylammonium bromide (CTAB) as raw materials, by using a simple hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and UV–visible diffuse reflectance spectroscopy (UV–vis DRS) were used to characterize the samples. It was found that tetragonal star-shaped Bi5O7Br crystals with high crystallinity could be obtained as pH value of the solution was about 9. Compared with flaky BiOBr particles, the star-shaped Bi5O7Br sample displayed red-shift in the UV–visible absorption edge, whereas the band gap was reduced to 2.57 eV and the specific surface area was increased. Among all samples, the star-shaped Bi5O7Br had the highest photocatalytic efficiency. After visible light irradiation for 10 min, the degradation rate of the rhodamine B (RhB) solution with a concentration of 10 mg·L−1 was almost 100%. Also, its photocatalytic activity was nearly unchanged after five cycles. It is believed that such Bi5O7Br could be used as stable and effective visible light catalysts.

Synthesis, photophysical, electrochemical and computational study of indolocarbazole based donor acceptor type conjugated polymers

This research reports the synthesis and characterization of two new donor–acceptor type conjugated polymers carrying indolocarbazole as donor, benzothiadiazole and diketopyrrolopyrrole as acceptor via stille coupling polymerization reactions. The structures of the polymer were established by spectroscopic techniques and polymer molecular weight by gel permeation chromatography. Further the linear optical and electrochemical properties of the polymers have been investigated. Polymers showed broad absorption and good fluorescence behaviour with good quantum yields. Optical bandgaps of the polymers were estimated using UV–visible absorption edge and found to be 2.34 and 2.12 eV respectively. Further, theoretical evaluation of the polymers was carried using density functional theory to investigate their geometrical, electrochemical and optical properties using DFT/B3LYP. The obtained results are in good agreement with the experimental results.

Single-step synthesis of Fe-TiO2 nanotube arrays with improved light harvesting properties for application as photoactive electrodes

Research on TiO2 nanotubes gained prominence in the past years due to their photoelectrochemical behavior. Metallic ion doping via a simple and fast method of production can dictate a path in order to achieve and improve such application. This work reports an innovative single-step anodization synthesis of iron-doped TiO2 nanotubes. Titanium foils were anodized at three potentials (20, 40 and 60 V) for 1 h. The resulting arrays were characterized by scanning electron microscopy, X-ray diffraction, Raman, XPS and UV–Vis diffuse reflectance spectroscopy. SEM images showed that higher anodization potentials successfully produced Fe-TiO2 nanotubes without a passivating top-layer. XRD and Raman results indicate that Fe ions were introduced in the anatase framework. Fe-doping produced a shift in the UV–Vis absorption edge towards the visible region, which reflected onto the photoelectrochemical performance of the electrodes. The Fe-TiO2 sample anodized at 60 V developed a current density of 1.9 × 10−4 A·cm−2, i.e., 2.5 times greater than that of the undoped TiO2 sample. The results indicate that the obtained Fe-TiO2 nanotube arrays are promising materials for application as photoactive electrodes.

Using thiol-amine solvent mixture to prepare main group heterometallic chalcogenides

By using a n-butylamine (BA)-1,2-ethanedithiol (EDT) solvent mixture as reaction medium, three new heterometallic chalcogenides have been prepared, namely [HBA]2.6[In2.6Sn1.4Se6S2] (1), [HBA]0.8[HR-MP]2[In2.8Sn1.2Se6S2] (2) (R-MP = (R)-2-methylpiperazines) and [H3TAEA]2[InGe4S11(SH)2(OH)] (3) (TAEA = tris(2-aminoethyl)amine). Compounds 1 and 2 feature anionic two-dimensional [InxSn4-xSe6S2]x− layers built up by [M4Q10] (M = In/Sn, Q = Se/S) T2 clusters. Protonated HBA+ and HR-MP+ cations serve as charge balance agents located between the layers. Compound 3 contains discrete [InGe4S11(SH)2(OH)]6− anionic clusters, in which the In3+ ion adopts a unique penta-coordination geometry with five S2− ions. These compounds were characterized by single crystal X-ray diffraction, powder X-ray diffraction, energy dispersive X-ray spectroscopy, solid-state UV–Vis diffuse reflectance spectroscopy, and thermogravimetric analyses. The steep UV–Vis absorption edges indicate the band gaps of 1.86 eV for 1, 2.13 eV for 2 and 2.78 eV for 3.

Thin film characterization of Ce and Sn co-doped CdZnS by chemical bath deposition

Abstract Cerium and tin co-doped cadmium zinc sulfide nanoparticles (CdZnS:Ce)Sn were synthesized by chemical bath deposition method with a fixed concentration of Ce (3.84 mol%) and three different concentrations of Sn (2 mol % and 4 mol% and 6 mol%). They showed broad photoluminescence spectra in the visible region under the ultraviolet excitation with a wavelength of 325 nm. The photoluminescence emission peaks were obtained at 540 nm, 560 nm and 570 nm for CdZnS, CdZnS:Ce and (CdZnS:Ce)Sn thin films, respectively having different concentrations of Sn. It has been observed that the photoluminescence emission peak shifted to higher wavelength region with an increase in intensity by Ce doping and Ce–Sn co-doping. Further enhancement in luminescence peak intensity has been observed by increasing concentration of Sn in (CdZnS:Ce)Sn films. Average crystallite size, measured from XRD data, was found to be increased with increasing concentration of Sn. An increase in the concentration of Sn shifted the UV-Vis absorption edge toward the higher wavelength side. Energy band gap for undoped CdZnS and Ce–Sn co-doped CdZnS varied from 2.608 eV to 2.405 eV. The SEM micrographs of CdZnS and (CdZnS:Ce)Sn films showed the leafy-like and ball-like structures. The presence of Sn and Ce was confirmed by EDAX analysis.

Synthesis, crystal structure, optical absorption study, and electronic structure of Cs3FeCl5

The single crystals of Cs3FeCl5 were synthesized at 973 K using the sealed tube solid-state molten flux method using CsCl as a reactive flux. The polycrystalline sample of Cs3FeCl5 was obtained by the stoichiometric reaction of CsCl and FeCl2 powders at 823 K by the sealed tube solid-state method. The crystal structure of Cs3FeCl5 was determined by single-crystal X-ray diffraction study at 298 (2) K. This ternary halide crystallizes in the body-centered tetragonal crystal system in I4/mcm space group with cell constants of a = b = 9.279 (1) Å and c = 14.824 (3) Å with four formula units per cell. The asymmetric unit of Cs3FeCl5 contains five crystallographically independent atomic sites: Cs1 (site symmetry: m.2 m), Cs2 (422), Fe1 (4¯2 m), Cl1 (..m), and Cl2 (4/m..). Each Fe atom in Cs3FeCl5 structure is bonded to four Cl1 atoms in a slightly distorted tetrahedral fashion to form isolated FeCl42− units. These FeCl42− units are separated by the Cs+ cations and infinite [CsCl] linear chains. Charge balance in this closed-shell compound can be achieved by 3 × Cs+, 1 × Fe2+, and 5 × Cl−. Bond valence sum (BVS) calculation also supports this assignment of formal oxidation states of elements in Cs3FeCl5 structure. The electronic structure calculation for Cs3FeCl5 performed within a density functional theoretical framework predicts a band gap of 3.5 eV, which is in good agreement with the experimental band gap of 3.71 (2) eV, that was estimated from the UV–vis absorption edge study of polycrystalline Cs3FeCl5.

RETRACTED ARTICLE: Fabrication of Hexagonal Disc Shaped Nanoparticles g-C3N4/NiO Heterostructured Nanocomposites for Efficient Visible Light Photocatalytic Performance

A hexagonal shaped nickel oxide/graphitic carbon nitride (NiO/g-C3N4) heterojunction composite was synthesized via a facile microwave irradiation route joint with succeeding calcination process. The structural, morphological and optical properties of the catalysts were characterized by XRD, TEM, Raman, UV–DRS, PL and BET analysis. XRD and TEM results exposed that cubic structure and with two dimensional hexagonal discs shaped morphology with sizes in the range of 30–40 nm. The incorporation of g-C3N4 caused a red-shift of the UV–Vis absorption edge of NiO. Moreover, exfoliation of bulk g-C3N4 into two dimensional g-C3N4 nanodiscs offers large surface area (102 m2/g) and exposed active sites, which are beneficial for photocatalytic activity enhancement. The photocatalytic activity of the photocatalysts was analyzed by degradation of congo-red and malachite green (MG) under induced visible light irradiation. The results demonstrates that NiO/g-C3N4 with 1.2 mass ratios shows the optimal overall photocatalytic performance such as huge degradation efficiency (97%), high rate constant (0.02012 min−1) and high stability (only loss ~ 3.5) after 7 cycles test (for MG dye). The superior photoactivity of NiO–g-C3N4 photocatalysts possibly will be recognized to the successful interfacial charge transfer between NiO and g-C3N4, thus suppressing the recombination of the photoexcited electron–hole pairs.

Large exciton binding energy, high photoluminescence quantum yield and improved photostability of organo-metal halide hybrid perovskite quantum dots grown on a mesoporous titanium dioxide template

Herein, we demonstrated a novel synthetic route to grow size-tunable hybrid perovskite (CH3NH3PbI3 and CH3NH3PbBr3) quantum dots (QDs) using a Fluorine-doped TiO2 (F-TiO2) mesoporous template and these QDs exhibit large exciton binding energy, high photoluminescence quantum yield and improved photostability. The pore size in F-TiO2 template is tuned by varying the HF molar concentration during its solvothermal growth and size of the perovskite QDs embedded in F-TiO2 pores is tuned in the range 1.7–5.1 nm, as revealed from the TEM analysis. A systematic blue-shift in UV–visible absorption edge, as well as photoluminescence (PL) spectrum, is observed with the reduced size of the perovskite QDs due to strong quantum confinement. The CH3NH3PbI3 QD with average size ∼1.7 nm exhibits ∼47 nm blue shift in the PL spectra, ∼43 fold enhancement in PL intensity and ∼25% PL quantum yield (QY). On the other hand, CH3NH3PbBr3 QD of similar size exhibits dramatically enhanced (∼124 times) PL emission with narrow line width and a PLQY of ∼57%, which is significant for the template-assisted growth of perovskite QDs film. The quantitative analysis of the PL emission energy vs QD size shows an excellent fit with the Brus equation confirming the strong quantum confinement effect in the perovskite QDs. Analysis of low-temperature PL spectra reveals very high exciton binding energy (162–272 meV) for the QDs as compared to the bulk film (32 meV) due to the high effective dielectric constant, and high electron-hole recombination probability in the QDs, which is consistent with the extremely high PLQY and stable emission from the QDs. The blue shift of the PL peak with increasing temperature is explained on the basis of localization effect. Time-resolved PL analysis for both the perovskite QDs reveals faster life time compared to their bulk counterparts, confirming the significant radiative recombination of carriers in the QDs at the room temperature. The CH3NH3PbBr3 QDs embedded in porous F-TiO2 template maintain its initial PL intensity up to several hours (≥10 h) under the UV laser exposure (18mW), while that of the bulk film decreases to <67%. Thus, template grown hybrid perovskite QDs exhibiting high photostability and very high PLQY demonstrated here are promising for the next generation optoelectronic applications.

Enhanced photoelectrochemical water oxidation on WO3 nanoflake films by coupling with amorphous TiO2

High surface states induced photoelectrochemical (PEC) activity and stability issue is the major performance bottleneck for nanostructured WO3 photoanode. Here we report that amorphous TiO2 (α-TiO2) be used as passivator to modify the surface states of WO3 nanoflakes film for improving its PEC water oxidation performance. In comparison with bare WO3 film, the α-TiO2-coupled WO3 (α-TiO2/WO3) film is of higher PEC water oxidation activity and stability. The photocurrent on α-TiO2/WO3 film photoanode is improved by 2 times that reached 1.4 mA/cm2 in 0.1 M Na2SO4 solution at 0.8 V (vs. SCE). After α-TiO2 coupling, the UV–vis absorption edge and intensity of WO3 film do not change obviously, but the formation and oxidation kinetics of H2O2 on WO3 photoanode are modified. The density functional theory calculations indicate the monoclinic WO3(002) has a surface energy of 1.17 J/m2, whereas the α-TiO2/WO3(002) with a much lower surface energy of 0.3 J/m2. Additionally, the length of TiO bond of α-TiO2 is changed from the initial 1.929 Å to a shorter length of 1.886 Å and a longer length of 2.290 Å in α-TiO2/WO3(002) through the O2--W6+ bonding effect at α-TiO2/WO3 interface. Therefore, the enhanced PEC water oxidation performance on α-TiO2/WO3 film can be attributed to that α-TiO2 passivates the surface states of WO3 nanoflakes film, and the formation of H2O2 from the photoexcited-electrons/dissolved-oxygen route is depressed and the PEC oxidation of H2O2 is accelerated.

Enhanced photocatalytic performance of silver–based solid solution heterojunctions prepared by hydrothermal method

Silver–based solid solution with phase heterojunctions (α/β–AgAl0.4Ga0.6O2 heterostructure) was fabricated through phase transformation under hydrothermal treatment. X–ray diffraction and Raman spectra showed the phase transformation behavior, phase structure and composition of the samples. Transmission electron microscopy illustrated the mixed morphology of near–spherical β phase together with platelet α phase and the formation of phase heterojunctions. UV–vis absorption edges of the α/β–AgAl0.4Ga0.6O2 heterostructure were adjusted from 470 to 515 nm by controlling phase ratio under different hydrothermal temperatures. The heterostructure displayed the enhanced photocatalysis activity for the degradation of methyl orange in comparison to single α or β phase. In addition, electrochemical properties including small diameter of the arc radius and maximum photocurrent indicated high separation and fast transfer efficiency of the photoinduced carriers across the phase heterojunctions. Therefore, both of the enhanced utilization of visible light and efficient carrier separation of α/β–AgAl0.4Ga0.6O2 heterostructure contributed to its excellent photocatalysis property.