Search

All-inorganic perovskite semiconductors have received significant interest for their potential stability over heat and humidity. However, the typical CsPbI3 displays phase instability despite its desirable bandgap of ~1.73 eV. Herein, we studied the mixed halide perovskite CsPbI2Br by varying the silver doping concentration. For this purpose, we examined its bandgap tunability as a function of the silver doping by using density functional theory. Then, we studied the effect of silver on the structural and optical properties of CsPbI2Br. Resultantly, we found that ‘silver doping’ allowed for partial bandgap tunability from 1.91 eV to 2.05 eV, increasing the photoluminescence (PL) lifetime from 0.990 ns to 1.187 ns, and, finally, contributing to the structural stability when examining the aging effect via X-ray diffraction. Then, through the analysis of the intermolecular interactions based on the solubility parameter, we explain the solvent engineering process in relation to the solvent trapping phenomena in CsPbI2Br thin films. However, silver doping may induce a defect morphology (e.g., a pinhole) during the formation of the thin films.

All-inorganic cesium lead bromide (CsPbBr3) quantum dots (QDs) have received a surge of attention in the field of light-emitting diode (LED) display and lighting. Hence, it is interesting to study the composite film composed of CsPbBr3 and light-emitting MDMO-PPV matrix polymer. In this study, we investigate the phase behavior among the components, MDMO-PPV, toluene (solvent), and oleic acid and oleylamine (the surface ligands for QDs) based on the Flory-Huggins theory with the group contribution method for the first time. Here we find that the MDMO-PPV and ligand molecules are immiscible whereas MDMO-PPV and toluene are partially miscible. Then through the x-ray diffraction (XRD) patterns, we demonstrate that CsPbBr3 QDs form a nanoscale domain with ∼33–52 nm crystallites in the MDMO-PPV matrix. Furthermore, the scanning electron microscope (SEM) images display that CsPbBr3 QDs can be highly aggregated at MDMO-PPV:CsPbBr3= 50:50 composition. Then, through the ultraviolet-visible (UV–vis) and photoluminescence (PL) spectra, the enhancement of PL intensity is observed at ∼30–50 wt% CsPbBr3. Finally, the electrochemical impedance spectra indicate that the composite film exhibits less resistance (∼3.2×104 Ω) than the pure MDMO-PPV film (∼1.4×107 Ω), suggesting that the MDMO-PPVCsPbBr3 composite approach is promising for electrochemical and optoelectronic applications.

The phase change of all-inorganic cesium lead halide (CsPbI3) thin film from yellow δ-phase to black γ-/α-phase has been a topic of interest in the perovskite optoelectronics field. Here, the main focus is how to secure a black perovskite phase by avoiding a yellow one. In this work, we fabricated a self-doped CsPbI3 thin film by incorporating an excess cesium iodide (CsI) into the perovskite precursor solution. Then, we studied the effect of organic additive such as 1,8-diiodooctane (DIO), 1-chloronaphthalene (CN), and 1,8-octanedithiol (ODT) on the optical, structural, and morphological properties. Specifically, for elucidating the binary additive–solvent solution thermodynamics, we employed the Flory–Huggins theory based on the oligomer level of additives’ molar mass. Resultantly, we found that the miscibility of additive–solvent displaying an upper critical solution temperature (UCST) behavior is in the sequence CN:DMF > ODT:DMF > DIO:DMF, the trends of which could be similarly applied to DMSO. Finally, the self-doping strategy with additive engineering should help fabricate a black γ-phase perovskite although the mixed phases of δ-CsPbI3, γ-CsPbI3, and Cs4PbI6 were observed under ambient conditions. However, the results may provide insight for the stability of metastable γ-phase CsPbI3 at room temperature.

Recently, tuning the green emission of CsPbBr3 quantum dots (QDs) to blue through quantum size and confinement effects has received considerable attention due to its remarkable photophysical properties. However, the synthesis of such a blue-emitting QD has been challenging. Herein, supersaturated recrystallization was successfully implemented at room temperature to synthesize a broadband blue-emitting ZnBr2-doped CsPbBr3 QD with an average size of ~3 nm covering the blue spectrum. The structural and optical properties of CsPbBr3 QDs demonstrated that QD particle size may decrease by accommodating ZnBr2 dopants into the perovskite precursor solution. Energy-dispersive spectroscopy confirmed the presence of zinc ions with the QDs. This work provides a new strategy for synthesizing strongly quantum-confined QD materials for photonic devices such as light-emitting diodes and lighting.

Room temperature (RT) synthesis of the ternary cesium lead bromide CsPbBr3 quantum dots with oleic acid and oleylamine ligands was developed by Zeng and coworkers in 2016. In their works, the supersaturated recrystallization (SR) was adopted as a processing method without requiring inert gas and high-temperature injection. However, the oleic acid ligand for haloplumbate is known to be relatively unstable. Hence, in this work, we employed the eco-friendly olive oil to replace the oleic acid portion for the SR process at RT. Resultantly, we found that the cube-shaped nanocrystal has a size of ~40–42 nm and an optical bandgap of ~2.3 eV independent of the surface ligands, but the photoluminescence lifetime (τav) and crystal packing are dependent on the ligand species, e.g., τav = 3.228 ns (olive oil and oleylamine; here less ordered) vs. 1.167 ns (oleic acid and oleylamine). Importantly, we explain the SR mechanism from the viewpoint of the classical LaMer model combined with the solvent engineering technique in details.

Water pollution by organic contaminants is one of the most severe issues confronting the world today as a result of the rapid increase of industrialization, urbanization, human population growth, and advances in agricultural technologies. Several attempts have been made to address global water pollution issues by utilizing conventional wastewater treatment technologies. However, conventional wastewater treatment methods have several limitations such as low efficiency, high operation costs, generation of secondary waste, require additional chemicals as oxidants and extra energy. Therefore, Heterogeneous photocatalysis has gained a lot of attention in the degradation of persistent organic pollutants because it combines high efficiency, environmental friendliness, cheap cost, and safety. Subsequently, the designing of novel nanocomposite photocatalysts with strong visible light-harvesting ability, efficient charge separation and transportation, and superb stability is imminently desired for wastewater treatment. Recently, the notion of combining g-C 3 N 4 with TiO 2 to design high photocatalytic performance heterojunction photoactive nanocomposites for organic pollutant degradation has received a lot of attention. Meanwhile, the construction of g-C 3 N 4 /TiO 2 -based heterojunction nanocomposites may enhance the ability of harvesting visible light, boost charge separation and transfer efficiency, and robust photocatalytic activity. Firstly, this review concisely explained the main sources of water pollution, as well as potential treatment approaches and the fundamental mechanism of heterogeneous photocatalysis. Subsequently, the details of properties, synthesis techniques, photoactivity modification strategies, and photocatalytic applications of g-C 3 N 4 , TiO 2, and g-C 3 N 4 /TiO 2 heterojunction photocatalysts are presented. Following that, the recent advances aimed at improving the photocatalytic performance of various types of visible-light-driven g-C 3 N 4 /TiO 2 heterojunction photocatalysts for organic pollutant degradation in wastewater are presented in detail. Finally, some concluding remarks and perspectives on the challenges and opportunities for constructing different types of g-C 3 N 4 /TiO 2 -based heterostructured photocatalysts are presented.

Recently, polymeric graphitic carbon nitride (g-C3N4) has been explored as a potential catalytic material for the removal of organic pollutants in wastewater. In this work, graphitic carbon nitride (g-C3N4) photocatalysts were synthesized using mixtures of low-cost, environment-friendly urea and thiourea as precursors by varying calcination temperatures ranging from 500 to 650 °C for 3 h in an air medium. Different analytical methods were used to characterize prepared g-C3N4 samples. The effects of different calcination temperatures on the structural, morphological, optical, and physiochemical properties of g-C3N4 photocatalysts were investigated. The results showed that rhodamine B (RhB) dye removal efficiency of g-C3N4 prepared at a calcination temperature of 600 °C exhibited 94.83% within 180 min visible LED light irradiation. Photocatalytic activity of g-C3N4 was enhanced by calcination at higher temperatures, possibly by increasing crystallinity that ameliorated the separation of photoinduced charge carriers. Thus, controlling the type of precursors and calcination temperatures has a great impact on the photocatalytic performance of g-C3N4 towards the photodegradation of RhB dye. This investigation provides useful information about the synthesis of novel polymeric g-C3N4 photocatalysts using a mixture of two different environmentally benign precursors at high calcination temperatures for the photodegradation of organic pollutants.

The pristine WO _3 (tungsten trioxide) and Cu/Ni Co-doped WO _3 nanoparticles were synthesized by the co-precipitation synthesis methods with fixed wt.% of nickel, i.e., 5 wt.%, and different wt.% of copper, i.e., 2, 3, 5 wt.%. The structural, optical and electrical properties, as well as the surface morphology were investigated thoroughly by various characterization techniques. All the doped/co-doped and un-doped samples had an orthorhombic structure, according to the XRD measurements. The XRD results further confirmed that the average crystalline size ranged from 46 to 25 nm after the dopant concentration was introduced. Reflectance spectroscopy was used to investigate the optical properties of the prepared nanomaterials and revealed that the optical band gap varied from 2.80 to 2.63 eV with dopant concentrations. The room temperature photoluminescence study showed that the emission peaks were observed in the visible region with slight peak shift towards short wavelength with dopant concentrations. The FTIR studies described the different mode of band related to a functional groups present in the materials and the stretching mode of O–W–W observed from 550 to 1050 cm ^−1 . The I-V studies confirmed that the prepared samples had a good ohmic contact behavior and the resistivity decreased from 6.3 × 10 ^−3 Ω.cm to 0.63 × 10 ^−3 Ω.cm with doping concentrations.

In this work, the un-doped, Cu-doped, and (Ni, Cu) co-doped SnO2 nanoparticles (NPs) were synthesized using the sol–gel method with a fixed concentration of copper dopant while varying the nickel concentrations. The structural, optical and electrical properties, as well as the surface morphology, were investigated systematically by various characterization techniques. The X-ray diffraction (XRD) study confirmed that the prepared samples had a tetragonal rutile crystal structure for all single-doped/co-doped and un-doped SnO2 NPs. The XRD results further confirmed that the crystalline sizes varied from 16 to 10 nm with the concentrations of the dopants. The UV–Vis diffusion reflectance spectroscopy (DRS) analysis showed that the optical band gap was found to be decreased from 3.38 to 3.27 eV when the dopant concentrations were increased. The energy dispersive analysis of X-ray spectra (EDX) results confirmed the presence of the expected elements in the prepared samples. Three major photoluminescence (PL) emission peaks were observed in the visible region, with a small shift toward lower wavelengths with dopant and co-dopant concentrations. Chemical bonding and the position of the O–Sn–O bond at 600–660 cm−1 were confirmed by the Fourier transform infrared spectroscopy (FTIR) study. The activation energies and conduction mechanisms of the prepared samples were investigated using the Hall Effect measurement method. The I–V studies confirmed that the prepared samples had a good ohmic contact behavior and the resistivity decreased significantly for co-doped sample. [ABSTRACT FROM AUTHOR]

Lead-free (Ba0.85Ca0.15) (Ti0.90Zr0.10)O3 (15/10 BCZT) piezoelectric ceramics were prepared by a standard solid solution and sintered at different temperature of 1300 °C and 1500 °C at a time. The 15/10BCZT piezoceramics were prepared at 1300 °C sintering temperature by doping different amount of MnO2.The ceramics show a phase transition from a freoelectric tetragonal phase to a rhombohedral and tetragonal ferroelctric phase and to a single rhombohedral phase with increasing MnO2 content. The addition of MnO2 significantly improves the sinterbility of the 15/10BCZT piezoceramics, and reducing the sintering temperature from 1500 °C to 1300 °C by 200 °C but showing comparable piezoelectric properties. With 0.4 mol% of the dopant, ∼96.5% of the theoretical density of the ceramics was achieved with excellent piezoelectric coefficient d33 ~ 534pC/N, which is nearly equal to the value obtained from the ceramics sintered at 1500 °C which has a piezoelectric coefficient d33 ~ 570pC/N, high density (~ 5.59 g/cm3), maximum remnant polarization (Pr = 24 μC/cm2), relatively large grain size (10.4 μm) and the least coercieve field (Ec = 0.42 kV/mm). However, a high concentration of MnO2 deterioated the properties of the ceramics because of increasing of oxygen vacancies and associated defects. The results indicate that the BCTZ-y mol% MnO2 ceramics are one of the promising lead-free piezoelectric candidates for high temperature applications. [ABSTRACT FROM AUTHOR]

We carried out a Rayleigh analysis of the dielectric permittivity of a lead-free piezoceramic system (1−x)(BaTi0.88Sn0.12)–x(Ba0.7Ca0.3)TiO3 across the composition and temperature induced polymorphic phase transformations to determine the trend in the reversible and irreversible domain wall motion across the composition and temperature induced structural changes. Experiments were carried out on three representative compositions x  =  0.10, 0.2, and 0.25 exhibiting rhombohedral, orthorhombic, and tetragonal phases at room temperature. While confirming that the irreversible Rayleigh parameter is large in the orthorhombic phase, we discuss a correspondence between the reduction in the coercive field and the corresponding increase in the irreversible Rayleigh parameter. We also show how the proximity of the Curie point to the polymorphic phase boundary greatly undermines this correspondence. [ABSTRACT FROM AUTHOR]