Search

The heavy‐metal‐free ZnSeTe quantum dots (QDs) hold great promise for the development of modern optoelectronic devices, yet, the nature of the emissive state within remains elusive. Herein, the different emission origins are clarified for the ZnSeTe QDs with dilute and heavy Te contents based on multiple spectroscopic characterizations and first‐principles calculation. In the case of dilute Te incorporation (Te/Se < 20%), the low‐energy tail of the asymmetric emission is ascribed to the recombination from the localized state induced by Te clusters, and the the hot carrier localization process occurs within a timescale of ≈500 fs. As the Te/Se ratio increases above 20%, the charge density difference shows a uniform distribution due to the decrease in electronegativity contrast, such that the carriers become delocalized and tail emission disappears. Meanwhile, the emission line‐width broadens mainly originating from the inhomogeneous broadening effect. These findings are constructive for developing sustainable QDs toward optoelectronic applications. [ABSTRACT FROM AUTHOR]

Transient optical response in perovskite quantum dots (QDs) has remained elusive until now, which hinders their full utilization in optoelectronics. Herein, we reveal that the bandgap renormalization (BGR) dictates the main spectral and dynamical features of transient response in CsPbBr3 QDs. By monitoring the absorption spectral evolution of the monodispersed QDs, the representative BGR is explicitly observed, giving rise to the photoinduced absorption at the higher energy side of the lowest exciton peak in transient absorption spectroscopy. The BGR gradually increases upon photoexcitation as a result of the carrier distribution dependent screening effect. We further demonstrate that the BGR arises from both Coulomb screening and phonon heating under high pump intensities in CsPbBr3 QDs. The synergistic effect leads to the giant BGR energy (ΔE > 60 meV) and the unconventional relationship of ΔE ∝ n1/2, where n is the carrier density. These findings are important for the fundamental understanding and potential applications of the emerging halide perovskite semiconductors. [ABSTRACT FROM AUTHOR]

Semiconductor heterostructures hold the promise for developing novel integrated devices with on‐demand photonic and optoelectronic properties. Herein, the perovskite lateral heterostructures in forms of microplates and microwires are fabricated by precise control of two‐step atmospheric pressure chemical vapor deposition course and the unique optical properties are demonstrated for the first time. The comprehensive spectroscopic and elemental mapping characterizations reveal the core‐shell‐like configuration of the individual heterostructure, which features the fascinating energy routing nature. Taking advantage of the effective photon recycling and the energy transfer processes, the record‐low threshold (≈3.5 µJ cm−2) lasing and the indirect pumping induced lasers from the single micro‐heterostructure are demonstrated. Moreover, the distinctive optical waveguides with propagation length independent output spectra from the microwire heterostructure are realized. These findings represent a significant advance in developing novel and functional optoelectronic devices by engineering the perovskite heterostructure. [ABSTRACT FROM AUTHOR]

Microlasers play an important role in the development of photonics and optoelectronics. As the rising star in the semiconductor family, all-inorganic lead halide perovskites (ILHPs) have been recognized as promising optical gain and lasing media. However, until now, achieving duplicable and single-mode microlasers remains a taunting challenge. Herein, we fabricated rectangular-shaped ILHP microsheets by the chemical vapor deposition method. The single-crystalline nature and the atomically smooth surfaces of the sample enable the achievement of lateral-cavity Fabry–Pérot (F-P) microlasers. Specifically, the lasing characteristics including the wavelength, mode spacing, and Q-factors can be well-reproduced along the axial direction of the individual microsheet. By regulating the width of the ILHP microsheet, the desirable single-longitudinal mode F-P microlaser was eventually achieved. Our results provide an enabling coherent light source for optics-related applications. [ABSTRACT FROM AUTHOR]

The in operando monitoring of catalytic intermediates is crucial for understanding the reaction mechanism and for optimizing the reaction conditions to improve the efficiency of the catalytic protocol; however, until now, this has remained a daunting challenge. Herein, we investigated the interaction of CO2 and H2 with the Cu(111) surface in a CO2 hydrogenation model system by using the in operando technique of near‐ambient pressure X‐ray photoelectron spectroscopy, which is further assisted by ultraviolet photoemission spectroscopy and low‐energy electron diffraction (LEED) measurements. These techniques allowed the direct observation of CO2 dissociation into CO+O on the Cu(111) surface and the adsorption of O on the surface at room temperature. The intermediate HCOO− was unambiguously detected in the CO2+H2 environment, which corroborated the formate pathway for methanol formation on the Cu(111) surface. We further found that O coverage can prevent the build up of graphitic carbon on the Cu surface. By taking advantage of the competitive interplay between Cu−O and graphitic carbon, we have proposed a feasible strategy for inhibition of the formation of graphitic carbon by tuning the CO2 and H2 partial pressures, which may contribute to sustaining the active Cu catalyst under the reaction conditions. Methanol synthesis on catalytic Cu surface: Near‐ambient pressure X‐ray photoelectron spectroscopy measurements unravel the formate pathway for methanol synthesis on the Cu(111) surface and reveal a competing interplay between the Cu−O and graphitic carbon, which may provide a feasible strategy for inhibiting the formation of graphitic carbon by tuning the partial pressures of CO2 and H2 (see picture). [ABSTRACT FROM AUTHOR]

BiFeO3 (BFO) thin films were prepared on (111)Pt/Ti/SiO2/Si substrates via a sol–gel spin-coating method, and the influence of the annealing temperatures on the phase formation, the microstructure and the electrical properties was systematically studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and an HP 4294A precision impedance analyser and a ferroelectric material test system, respectively. The XRD analysis revealed the films to be well-crystallised, and those annealed at approximately 700°C were well-formed in the perovskite phase. The SEM images confirmed that the BFO films had a uniform and dense microstructure with an average thickness of 300nm. As the frequency increased to 1MHz, the dielectric constant of the BFO films remained stable and exhibited only a slight decrease. The film annealed at 715°C exhibited the best dielectric properties with a high dielectric permittivity (ε r=194 at 100kHz) and a low dielectric loss (tanδ=0.02 at 100kHz). The leakage current density of the BFO thin films was also notably low, i.e., 10−6 A/cm2, under an applied electric field of 200kV/cm for the film annealed at 715°C. The excellent electrical properties obtained in the sol–gel-derived BFO films are attributed to the improved phase purity and microstructure. [ABSTRACT FROM AUTHOR]

Colloidal zinc‐chalcogenide quantum dots (QDs) are emerging as the promising heavy‐metal‐free light–emitters, however, the development of light amplification and lasing therein remains challenging. Here, corroborated by comprehensive in situ and transient spectroscopy, it is unraveled that the ultrafast photooxidization‐induced trapping process (≈2 ps) and the sub‐bandgap photoinduced absorption under intense excitation are the main hindrances to light amplification in ZnSeTe QDs. Upon tackling the hurdle by heterostructure engineering, this study demonstrates that the ZnSeTe QDs exhibit intrinsically superior gain performance, including the high gain cross‐section (5.6 × 10−16 cm2), long gain lifetime (615 ps), low pump threshold (≈25.9 µJ cm−2) and high fatigue resistance. On this basis, a microfluidic channel is designed to mass‐produce the micellar cavities whose surfaces are treated to combine with the ZnSeTe QDs. The active QD‐micelle hybrids show state‐of‐the‐art lasing performance and allow the fiber‐based micro‐manipulation toward the single‐mode lasers. These findings not only provide essential knowledge on the gain physics in ZnSeTe QDs, but also open a new avenue to develop high‐performance eco‐friendly lasers. [ABSTRACT FROM AUTHOR]

All-inorganic cesium lead halide perovskites have been emerging as the promising semiconductor materials for next-generation optoelectronics. However, the fundamental question of how the environmental atmosphere affects their photophysical properties, which is closely related to the practical applications, remains elusive. Here, we report the dynamic switching between radiative exciton recombination and non-radiative carrier trapping in CsPbBr3 by controlling the atmospheric conditions. Specifically, we show that the photoluminescence (PL) intensity from the CsPbBr3 crystals can be boosted by ~ 60 times by changing the surrounding from vacuum to air. Based on the comprehensive optical characterization, near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) as well as density functional theory (DFT) calculations, we unravel that the physisorption of oxygen molecules, which repairs the trap states by passivating the PL-quenching bromine vacancies, is accountable for the enhanced PL in air. These results are helpful for better understanding the optical properties of all-inorganic perovskites. Perovskite-based optoelectronics are expected to become an important component of devices such as solar cells and light-emitting diodes. However, how they are affected by environmental conditions is still not fully understood. The authors investigate the mechanisms, which occur for inorganic perovskites when in contact with ambient atmosphere and how this could potentially impact upon device performance. [ABSTRACT FROM AUTHOR]

The electric field effect on the optical properties of semiconductors is important in terms of both fundamental physics and technological applications. Here, we explored the optical behavior of cesium halide perovskites under a varied electric field (F). We revealed the intrinsically distinct photoluminescence (PL) spectral evolution between the quantum-confined perovskites and the bulk phase, indicating the different carrier recombination behaviors under F. Strong PL quenching along with significant broadening of emission linewidths was observed. Notably, the CsPbBr3 colloidal quantum dots and nanoplatelets exhibit an unusual field-induced bandgap increase, which is attributed to the weakened orbital coupling between the Pb 6s and Br 4p states with the increase in F. These results could advance their application potential in optoelectronics. [ABSTRACT FROM AUTHOR]

BiFeO 3 (BFO) thin films doped differently with 5 mol% Mn 3+ and 5 mol% Mn 2+ were prepared on (111)Pt/Ti/SiO 2 /Si substrates by a sol–gel method with rapid thermal annealing. Systematic analyses about the two different doping effects and their underlying mechanisms were performed. Pure and doped BFO films were well crystallized in perovskite structure, whilst doping of Mn 3+ and Mn 2+ resulted in slight distortion in the lattice structure. After doping, smaller grain size, diminished structural defects and denser microstructure were confirmed. Both Mn 3+ and Mn 2+ dopants could reduce the concentration of oxygen vacancies in BFO films, whereas Mn 3+ doping exhibited better ability. As a result, the Mn 3+ doped film showed the highest dielectric permittivity among those three samples, ε r =105 at 100 kHz; meanwhile, the Mn 3+ doped film showed a superior 2 P r value of 79.5 µC/cm 2 , compared to 63.2 µC/cm 2 for the Mn 2+ doped film and unachievable intrinsic ferroelectric polarizations in the undoped BFO film because of high leakage contribution. The leakage current density in medium/high electric field region was dramatically decreased by Mn doping, accompanied with a change of conduction mechanism from the space charge limited conduction to the Schottky mechanism. [ABSTRACT FROM AUTHOR]

Developing a titanium dioxide (TiO2)‐based anode with superior high‐rate capability and long‐term cycling stability is important for efficient energy storage. Herein, a simple one‐step approach for fabricating blue TiO2 nanoparticles with oxygen vacancies is reported. Oxygen vacancies can enlarge lattice spaces, lower charge transfer resistance, and provide more active sites in TiO2 lattices. As a result, this blue TiO2 electrode exhibits a highly reversible capacity of 50 mAh g−1 at 100 C (16 800 mA g−1) even after 10 000 cycles, which is attributable to the combination of surface capacitive process and remarkable diffusion‐controlled insertion revealed by the kinetic analysis. The strategy of employing oxygen‐deficient nanoparticles may be extended to the design of other robust semiconductor materials as electrodes for energy storage. [ABSTRACT FROM AUTHOR]

Black phosphorus (BP) shows great potential in electronic and optoelectronic devices owing to its semiconducting properties, such as thickness-dependent direct bandgap and ambipolar transport characteristics. However, the poor stability of BP in air seriously limits its practical applications. To develop effective schemes to protect BP, it is crucial to reveal the degradation mechanism under various environments. To date, it is generally accepted that BP degrades in air via light-induced oxidation. Herein, we report a new degradation channel via water-catalyzed oxidation of BP in the dark. When oxygen co-adsorbs with highly polarized water molecules on BP surface, the polarization effect of water can significantly lower the energy levels of oxygen (i.e. enhanced electron affinity), thereby facilitating the electron transfer from BP to oxygen to trigger the BP oxidation even in the dark environment. This new degradation mechanism lays important foundation for the development of proper protecting schemes in black phosphorus-based devices. [ABSTRACT FROM AUTHOR]

Black phosphorus (BP) shows great potential in electronic and optoelectronic devices owing to its semiconducting properties, such as thickness-dependent direct bandgap and ambipolar transport characteristics. However, the poor stability of BP in air seriously limits its practical applications. To develop effective schemes to protect BP, it is crucial to reveal the degradation mechanism under various environments. To date, it is generally accepted that BP degrades in air via light-induced oxidation. Herein, we report a new degradation channel via water-catalyzed oxidation of BP in the dark. When oxygen co-adsorbs with highly polarized water molecules on BP surface, the polarization effect of water can significantly lower the energy levels of oxygen (i.e. enhanced electron affinity), thereby facilitating the electron transfer from BP to oxygen to trigger the BP oxidation even in the dark environment. This new degradation mechanism lays important foundation for the development of proper protecting schemes in black phosphorus-based devices. [ABSTRACT FROM AUTHOR]

Polycrystalline (Ba 0.70 Sr 0.30 )TiO 3 (BST) thin films were prepared by ion beam sputtering and postdeposition annealing method, and their crystallization kinetics was monitored in situ. It was found that 550 °C is a critical temperature for the BST׳s perovskite phase formation, below which a long annealing time is needed to obtain good perovskite structure because of a slow crystallization process, while generating much lower inhomogeneous and thermoelastic strains. As a consequence, the ferroelectric/paraelectric state formation in BST films, being strain sensitive, was purposefully tailored through simple kinetics instead of pure thermodynamics. A long time annealing at 530 °C induced a room temperature (RT) ferroelectric state, whereas the annealing at 550 °C and above promoted much faster perovskite crystallization and tailored the film at RT in its paraelectric state, thereby giving rise to two distinct dielectric behaviors. These findings provide important implications for simply controllable state growth of perovskite thin films with desired electrical properties so as to meet their respective requirements in different application fields. [ABSTRACT FROM AUTHOR]