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A method for achieving the accurate measurement of the antiferroelectric-ferroelectric (AFE-FE) phase switching time based on the electrically induced light scattering effect was designed. The AFE-FE switching times of lanthanum-modified lead zirconate titanate (PLZT) transparent ceramics decreased with the increase of the applied electric fields, and the logarithm of the switching time was approximately proportional to the electric field reciprocal. The random orientation of the polycrystalline structures with dispersion-distributed mixed phases of the PLZT transparent ceramics was the intrinsic mechanism affecting the corresponding switching times in the applied electric field. The smaller electrode size samples switched faster than the larger samples in the same electric field. The size effect of the switching times occurred due to the higher dielectric constant of the ceramics and the parameters of the test circuit, and the larger capacitance of the samples resulted in a longer rising time of the applied electric field, which in turn slowed down the phase switching and prolonged the switching time.

Deep-red luminescence emission makes CsPbI3 nanocrystals (NCs) promising materials for various applications, but their use is limited in practice by instability in moist ambient environments. Incor...

Low-dimensional lead-free metal halides, which feature strong quantum confinement effects, have recently attracted great attention due to their excellent optical properties and favorable stability under ambient conditions. Although controllable synthetic strategies, structural characterization and linear optical properties of lead-free metal halides have been widely reported, relevant studies on their nonlinear optical properties are still lacking, which hinders their applications in nonlinear photonic devices. Herein, two types of millimeter-level high-crystallinity cesium copper halide single crystals (SCs), i.e., Cs3Cu2I5 and CsCu2I3, with high photoluminescence (PL) quantum yields, are synthesized using an antisolvent vapor-assisted crystallization method. Their phonon energies are comparatively studied by using Raman spectroscopy and temperature-dependent PL spectroscopy. More importantly, comparison studies of the multiphoton absorption (MPA) properties of Cs3Cu2I5 and CsCu2I3 SCs are performed for the first time. Strong multiphoton excited PL emissions with large anisotropy factors are observed in these two types of SCs. Through the measurement of nonlinear transmittance, it is found that CsCu2I3 SCs exhibit much larger MPA coefficients compared with Cs3Cu2I5 SCs, which is attributed to the larger density of states in the former. This work broadens the applications of cesium copper halides in nonlinear optoelectronics and light polarization related devices.

Based on the extensive investigation on graphene and graphene derivatives asymmetrically functionalized with a variety of molecular groups and the concept of Janus materials with asymmetric facial properties, Janus two-dimensional (2D) materials as derivatives of the 2D material family, including Janus graphene, Janus transition metal chalcogenides, etc., have attracted much attention in recent years. Janus 2D materials have been demonstrated experimentally and theoretically to possess unique properties such as an out-of-plane piezoelectric polarization and strong Rashba effect due to their out-of-plane asymmetry. Here, the recent progress of emerging Janus 2D materials, including Janus graphene, prediction and fabrication of various different Janus 2D materials and Janus 2D van der Waals heterostructures, is presented. The investigations on the unique properties and potential device applications of Janus 2D materials are summarized. Finally, the conclusion and prospects for the future explorations on Janus 2D materials are also provided.

Hybrid organic-inorganic metal halides have emerged as highly promising materials for a wide range of applications in optoelectronics. Incorporating chiral organic molecules into metal halides enables the extension of their unique optical and electronic properties to chiral optics. By using chiral (R)- or (S)-methylbenzylamine (R-/S-MBA) as the organic component, we synthesized chiral hybrid copper halides, (R-/S-MBA)2 CuCl4 , and investigated their optical activity. Thin films of this material showed a record anisotropic g-factor as high as approximately 0.06. We discuss the origin of the giant optical activity observed in (R-/S-MBA)2 CuCl4 by theoretical modeling based on density functional theory (DFT) and demonstrate highly efficient second harmonic generation (SHG) in these samples. Our study provides insight into the design of chiral materials by structural engineering, creating a new platform for chiral and nonlinear photonic device applications of the chiral hybrid copper halides.

In recent years, it has witnessed a rapid development of the fluorescent carbon dots (CDs) due to their unique optical properties and wide range of applications. However, difficulties in synthesizing long wavelength-emitting CDs have been the major drawback of CDs, which limited their applications in fields such as bioimaging and carbon-based white light-emitting diodes. Herein, on the basis of surface electron state engineering, we prepared surface metal-ion-functionalized CDs by treating solvothermally synthesized CDs with alkali metal aqueous solutions (LiOH, NaOH or KOH). Especially, we focused the CDs treated with LiOH solution (Li-CDs) because these CDs’ absolute photoluminescence quantum yield is as high as 34% in dilute ethanol solution under 550 nm excitation compared with those treated with NaOH or KOH solutions. The electron transport effect of alkali metal ions was confirmed. Moreover, the obtained Li-CDs show high optical pH sensitivity within pH values 1–4.5 and were applied to pH sensing. This work not only proposes a feasible and controllable method to construct long wavelength-emitting CDs, but also shows the application potentiality such as pH sensing devices.

Crystalline calcium aluminates are a critical setting agent in cement. To date, few have explored the microscopic and dynamic mechanism of the transitions from molten aluminate liquids, through the supercooled state to glassy and crystalline phases, during cement clinker production. Herein, the first in situ measurements of viscosity and density are reported across all the principal molten phases, relevant to their eventual crystalline structures. Bulk atomistic computer simulations confirm that thermophysical properties scale with the evolution of network substructures interpenetrating melts on the nanoscale. It is demonstrated that the glass transition temperature (T g) follows the eutectic profile of the liquidus temperature (T m), coinciding with the melting zone in cement production. The viscosity has been uniquely charted over 14 decades for each calcium‐aluminate phase, projecting and justifying the different temperature zones used in cement manufacture. The fragile–strong phase transitions are revealed across all supercooled phases coinciding with heterogeneous nucleation close to 1.2T g, where sintering and quenching occur in industrial‐scale cement processing., The evolution mechanism of different calcium‐aluminate phases during fast heating to about 3200 K and subsequent cooling is revealed by measuring their associated thermophysical properties (e.g., viscosity and density) using the self‐developed aerodynamic levitation technique and by bulk‐scale computationally modeling these properties and the atomistic structural changes. The fragile‐to‐strong phase transitions are discovered across all supercooled calcium‐aluminate liquids.

The bismuth layer-structured Na0.5Bi4.5-xPrxTi4O15 (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) (NBT-xPr3+) ceramics were fabricated using the traditional solid reaction process. The effect of different Pr3+ contents on dielectric, ferroelectric and piezoelectric properties of Na0.5Bi4.5Ti4O15 ceramics were investigated. The grain size of Pr3+-doping ceramics was found to be smaller than that of pure one, the maximum dielectric constant and Curie temperature Tc gradually decreased with increasing Pr3+ contents, and the dielectric loss decreased at high temperature by Pr3+-doping. Moreover, the activation energy (Ea), resistivity (Z’), remanent polarization (2Pr) and piezoelectric constant (d33) increased by Pr3+-doping. The NBT-xPr3+ ceramics with x = 0.3 achieved the optimal properties with the maximum dielectric constant of 1109.18, minimum loss of 0.00822 (250 kHz), Ea of 1.122 eV, Z’ of 7.9 kΩ cm (725 oC), d33 of 18 pC/N, 2Pr of 12.04 μC/cm2. The enhancement was due to the addition of Pr3+ which suppressed the decreasing of resistivity at high temperature and made it possible for NBT-xPr3+ ceramics to be poled in perpendicular direction, implying that it is a great improvement for Na0.5Bi4.5Ti4O15 ceramics in electrical properties.

New lead-free dielectric ceramics, Na 1+x BiTi 6 O 14+0.5x (x = −0.02, − 0.01, 0.01, 0.02), were prepared by the conventional solid-state method. Micro-structural and electrical properties of Na 1+x BiTi 6 O 14+0.5x were studied. XRD showed all the samples exhibited a single structured phase. Grains decreased at the beginning, then grew with the increasing x content in SEM. Impedance spectra (IS) analysis evidenced the phenomena that the dielectric permittivity increased firstly, then decreased, while the loss had the opposite trend. Z* plots showed that Na 1+x BiTi 6 O 14+0.5x ceramics were a kind of dielectrics. The activation energy ( E a ) could be calculated in the range of 1.53–1.65 eV, which indicated they were dielectric ceramics. Na 1+x BiTi 6 O 14+0.5x ceramics (x = 0.01) sintered at 1040 °C showed prominent dielectric properties with a dielectric constant of 25.76, loss of 0.07%, E a of 1.65 eV, density of 3.463 g/cm 3 , impedance of 0.532 MΩ cm, -Z′′ max of 0.1958 MΩ cm, capacitance of 5.56 pF/cm (600 ℃), which were enhanced much compared with other samples. The existence of dielectric properties with high dielectric constant, low dielectric loss and wide operating temperature range makes it possible to develop the ceramics into high-temperature capacitors.

As a new member of lead-free Na 0.5 Bi 0.5 TiO 3 (NBT) ceramics based on bismuth layer-structured ferroelectrics (BLSFs), Bi x Ti 3 O 6+1.5 x ( x = 3.96, 3.98, 4.0, 4.02, 4.04) ceramics was prepared by a conventional mixed oxide route. In order to explore the ferroelectric and dielectric properties, we changed the content of Bi in the ceramics. XRD patterns of Bi x Ti 3 O 6+1.5 x demonstrated that the new material was a single phase of Bi-layered perovskite structure. Through impedance spectra analysis, we found that the Bi 4.02 Ti 3 O 12.03 ceramics sintered at 1100 °C showed excellent dielectric properties with a highest dielectric constant of 8967.49 and a lowest dielectric loss of 0.00298 measured under 10 kHz, which were enhanced much compared with Bi 4 Ti 3 O 12 prepared by the same means. Meantime, the Curie temperature of the whole samples was about 670 °C. In addition, the ferroelectric hysteresis loops of all the samples indicated that they were ferroelectric materials, and Bi 4 Ti 3 O 12 ceramics sintered at 1100 °C processed a remanent polarization (2 P r ) of 12.206 µC/cm 2 and a coercive field of 29.542 kV/cm. SEM can roughly describe the results of the dielectric spectrum and ferroelectricity with different Bi concentration through grain size mechanics. Because of the high dielectric constant, wide operating temperature and low dielectric loss, the Bi 4 Ti 3 O 12 ceramics have a broad application prospect in components, such as sensors, high-temperature capacitors and so on.

As a new kind family of lead-free Na0.5Bi0.5TiO3 (NBT) ceramics, bismuth layer-structured ferroelectrics (BLSFs), Na0.5BixTi3.98Mg0.02Oy (x = 4.48, 4.50, 4.52) were synthesized by a conventional mixed oxide route. Studies have found that the dielectric properties of Na0.5Bi4.5Ti4O15 can be optimized through changing the Bi content of the ceramics or Mg-doping on Ti-site under different sintering temperatures. X-ray diffraction analysis indicated that the new material was in a single BLSFs phase. The dielectric constant of Mg-doped Na0.5Bi4.5Ti3.98Mg0.02Oy was improved and dielectric loss of Na0.5Bi4.5Ti3.98Mg0.02Oy changed slowly under 500 °C with the increased sintering temperature. We found that the dielectric properties of the sample sintered at 1120 °C with the highest permittivity of 1122.5 and the lowest dielectric loss of 0.01 were relatively better than those of the other samples. SEM can be better to explain the results of the dielectric spectrum at different sintering temperatures through grain size mechanics. Z* plots showed that Na0.5Bi4.5Ti3.98Mg0.02Oy ceramics are a kind of dielectrics. Thus, Na0.5BixTi3.98Mg0.02Oy (x = 4.48, 4.50, 4.52) can be used as high-temperature capacitors and phase shifter with high dielectric constant, low dielectric loss and wide operating temperature range.

Perovskite nanocrystals (PeNCs) are attractive in high-color gamut display technology as light converters which can achieve saturated green and red lights, respectively. However, PeNCs are intrinsically fragile against ambient conditions, such as moisture and oxygen and it is hard to maintain their performance in long-term operation. In this work, a new hierarchical encapsulation method is proposed, integrated with surface modification by halide ions protection, nano-scaled encapsulation by in situ capping SiO2 and embedding into poly (methyl methacrylate) (PMMA) matrix composites, to achieve a stable perovskite light converting composite sheet for LED remote-type encapsulation. The storage stability, as well as the operational stability of perovskite composites, were confirmed by the spectra evolution from encapsulated LEDs with normalized blue emission intensity. The 2D maps of spectra and aging measurement indicate that the silica encapsulation can well protect the PeNCs in the PMMA matrix from the ambient circumstance during a long-term storage process. Additionally, the hierarchical encapsulation for PeNCs/silica/PMMA showed better operational stability than the direct encapsulation of PeNCs/PMMA, and the correspondent Commission Internationale de L'Eclairage color coordinates tracking also indicated more stable color properties, which demonstrates the great potential in photoluminescent display applications.

Chiral ligand conjugated transition metal oxide nanoparticles (NPs) are a promising platform for chiral recognition, biochemical sensing, and chiroptics. Herein, we present chirality-based strategy for effective sensing of mercury ions via ligand-induced chirality derived from metal-to-ligand charge transfer (MLCT) effects. The ligand competition effect between molybdenum and heavy metal ions such as mercury is designated to be essential for MLCT chirality. With this know-how, mercury ions, which have a larger stability constant ( K f ) than molybdenum, can be selectively identified and quantified with a limit of detection (LOD) of 0.08 and 0.12 nmol/L for D-cysteine and L-cysteine (Cys) capped MoO 2 NPs. Such chiral chemical sensing nanosystems would be an ideal prototype for biochemical sensing with a significant impact on the field of biosensing, biological systems, and water research-based nanotoxicology.

Using the vanadium oxyacetylacetone (VO(AcAc)2) as the precursor and white powdery tungstic acid as the doping W source, we fabricated the W-doped porous VO2 films by spin-coating method followed by annealing under the N2 atmosphere at 550 °C for half an hour. Compared to the pure VO2 film, the 5 at.% W-doped film exhibits a simultaneous enhancement of the near-IR switching efficiency at 2000 nm from 47.5 to 55.0 % and the maximum value of visible transmittance at 30 °C from 39.5 to 46.7 % as well as the one at 90 °C from 44.7 to 58.1 %, which further confirmed the practicability of introducing pores into the VO2 film as a strategy to enhance the thermochromic properties. In addition, a possible connection is presented about the relationship of metal–insulator transition process and the evolution of the phase compositions and morphology. A possible connection between the morphology and the thermochromic performance for the W-doped VO2 films was presented.

Transition metal oxides (TMOs) consist of a series of solid materials, exhibiting a wide variety of structures with tunability and versatile physicochemical properties. Such a statement is undeniably true for chiral TMOs since the introduction of chirality brings in not only active optical activities but also geometrical anisotropy due to the symmetry-breaking effect. Although progressive investigations have been made for accurately controlled synthesis and relevant explanations on the chirality origin of such materials, the overall field of chiral TMOs is still in its infancy with adequate space for interdisciplinary communications and development. Herein, therefore, recent advances in both experimental phenomena and theoretical calculations in this area are reviewed, to elucidate the underlying chiral origin with respect to their fabrications process, triggering new insights for further evolution of this field.

The increasing interest and rapid progress in the artificial neural networks have driven extensive research in resistive switching memory based on various insulators and two-dimensional nanomaterials. Herein, we have demonstrated a kind of resistive switching memory device based on GaSe layered nanorods fabricated by liquid phase exfoliation (LPE) method with a lateral graphene/GaSe/graphene structure. The single crystalline GaSe layered nanorods mixed with a few nanoflakes were synthesized by shear and ultrasonic (bath and probe) exfoliation methods, which showed high quality and hexagonal crystalline structure. The electrical properties and the resistive switching behavior were investigated, indicating the charge trapping/detrapping effect is the dominant resistive switching mechanism. This work suggests a novel strategy to develop the resistive switching devices based on various 2D materials by using LPE method, and these 2D-nanomaterials-based memristors have the potential to be used for constructing neuromorphic computing systems.

Due to their unique optoelectronic properties, doped semiconductor nanocrystals (NCs) are promising fluorescent probes for deep-tissue bioimaging applications. However, studies on the photophysical properties of cadmium-free doped NCs are scare. In this study, we synthesized and studied the photophysical properties of one type of cadmium-free doped NCs (Cu: ZnInS/ZnS NCs), which exhibit near infrared-I (NIR-I) emission at 730 nm and long emission lifetime up to 1.38 μs. Femtosecond transient absorption spectra revealed a strong exciton coupling effect between the Cu2+ ions and the ZnInS/ZnS host, with a fast energy transfer time of ≈100 ps. More importantly, Cu: ZnInS/ZnS NCs exhibit efficient volume-normalized two- and three-photon absorption cross-sections in NIR-I (800-900 nm) and NIR-III regions (1600-1990 nm), with maximum values up to 6.9 GM nm-3 at 800 nm and 1.1×10-80 cm6 s2 photon-2 nm-3 at 1600 nm, respectively. This study can shed light on the exploration of novel environmentally friendly doped NCs for deep-tissue bioimaging applications.

Porous thermochromic pure and tungsten (W)-doped vanadium dioxide (VO2) films have been prepared on silica substrates by spin coating via a sol–gel process and annealing in ammonia (NH3) atmosphere. NH3 with weak reducing capacity can prevent V4+ from further oxidization and contribute to the formation of porous structure. These films exhibit enhanced visible transparency and switching property at near-infrared wavelengths across the metal–insulator transition (MIT). The transmittance change in the VO2 film annealed at 2.0 × 103Pa is as high as 52.9 % at λ = 2000 nm, and its solar modulation efficiency reaches up to 9.4 %. W-doping shifts the MIT temperature of the VO2 films from 55 to 28 °C, while the films remain the excellent modulating ability in near-infrared region, and the decreasing efficiency of V0.99W0.01O2 film can achieve to 20 K/at.%, which will greatly favor the practical application of VO2-based smart windows. Transmittance spectra for pure VO2 film in the range of 250–2500 nm and the recorded transmittance–temperature hysteresis loop in the range of 20–90 °C of the W-doping VO2 films after annealing at 500 °C for 30 min (middle inset).

La0.67Sr0.33MnO3 (LSMO) films were prepared on SrTiO3 single-crystal substrates by the pulsed laser deposition method. X-ray photoelectron spectra (XPS) were measured for the LSMO films as-prepared, annealed in oxygen and in vacuum, respectively. Multiple peaks fitting for Mn 2p3/2 XPS spectra shows that Mn2+ appears and the ratio of Mn3+/Mn4+ increases on the surface of LSMO film annealed in vacuum comparing with the as-prepared film, though the saturation magnetization (Ms) changes little. Mn6+ and Mn7+ can be detected while Mn4+ decreases much on the surface of LSMO film annealed in oxygen. The change of Mn3+/Mn4+ results in the obviously reduce of Ms. O1s spectra show the gradual changes of Mn-O, Sr-O and La-O. Analysis indicates that Mn2+ forms at the surface defects of LSMO films. Annealing in vacuum hardly affects the magnetic property of LSMO films. But annealing in oxygen greatly changes the valence states of Mn, which weakens the magnetic property of LSMO films.