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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...

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.

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.

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).

Amorphous GeSex (x = 2, 4, 6) films were prepared by pulsed laser deposition technique. The optical band gaps ( E g opt ) and refractive indices of the films were derived from the absorption spectra and optical transmission spectra, respectively. The short-wave absorption edges of the films were well consistent with the ‘non-direct transition’ model proposed by Tauc. The dispersion of the refractive index was analyzed in terms of the single-oscillator Wemple–Di Domenico model. The structural units of the films were characterized using Raman spectroscopy. In addition to the basic structural units of edge-sharing GeSe4/2 tetrahedra, there are Se Se homopolar bonds in Se-rich GeSe4 and GeSe6 films. And Ge Ge bonds exist in stoichiometric GeSe2 film. The results also show that the refractive index of the films changes with the Se content. E g opt decreases with the reduction of Se content in the GeSex films. The changes of E g opt were discussed in relation to the structures of the films confirmed by the Raman spectra analysis.

The 80-nm-thickness BaTiO 3 (BT) thin film was prepared on the Pt/Ti/SiO 2 /Si substrate by the RF magnetron sputtering technique. The Pt/BT/Pt/Ti/SiO 2 /Si structure was investigated using X-ray diffraction and scanning electron microscopy. The current–voltage characteristic measurements were performed. The bipolar resistive switching behavior was found in the Pt/BT/Pt cell. The current–voltage curves were well fitted in different voltage regions at the high resistance state (HRS) and the low resistance state (LRS), respectively. The conduction mechanisms are concluded to be Ohmic conduction and Schottky emission at the LRS, while space-charge-limited conduction and Poole–Frenkel emission at the HRS. The electroforming and switching processes were explained in terms of the valence change mechanism, in which oxygen vacancies play a key role in forming conducting paths.

Ho3+ doped Ba0.65Sr0.35TiO3 (BST) nanocrystals was prepared by sol–gel method. The structural and morphological properties of the nanocrystals were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The absorption spectrum, photoluminescence spectrum and fluorescence time decay curve were measured at room temperature. Based on the Judd–Ofelt (J–O) theory, the J–O intensity parameters Ωt (t=2, 4, 6) of Ho3+ doped BST nanocrystals were calculated to be 0.67×10−20 cm2, 1.11×10−20 cm2 and 1.09×10−20 cm2, respectively. The emission probabilities, radiative lifetimes and branching ratios of the different Ho3+ transitions were also determined. The emission cross sections of the important intermanifold transitions 5F4, 5S2→5I8, 5F5→5I8 and 5F4→5I7 have been calculated from the luminescence spectrum. The room temperature fluorescence lifetime of the 5S2→5I8 transition for Ho3+ in BST nanocrystals was measured and the radiative quantum efficiency was estimated to be 61.9%.

Amorphous GeS x (x = 2, 4, 6) films were prepared by the pulsed laser deposition (PLD) technique. The optical band gaps ( E g opt ) and refractive indices of the films were obtained from the optical absorption spectra and transmission spectra, respectively. The short-wave absorption edges of the films were described using the ‘non-direct transition’ model proposed by Tauc. The dispersion of the refractive index was analyzed in terms of the single-oscillator Wemple–Di Domenico model. The structural units of the films were characterized using Raman spectroscopy. In addition to the basic structural units of edge-sharing and corner-sharing [GeS 4 ] tetrahedra, there are S–S homopolar bonds in S-rich GeS 4 and GeS 6 films while Ge–Ge bonds exist in stoichiometric GeS 2 film. The results show that the index of refraction decreases while E g opt increases with the sulphur content in the GeS x films. The changes of E g opt were discussed in relation to the structure of GeS x films, which were confirmed by the Raman spectra analysis.

Ba0.8Sr0.2TiO3 ceramics were prepared by the conventional solid-state reaction method. The effects of different calcining and sintering temperatures on pyroelectric properties of the ceramics were investigated. The TG-DTG test was used to determine the calcining temperature. The XRD results showed that all samples were perfect perovskite structure. SEM results exhibited a homogeneous grain dimensions distribution and dense microsructure in the samples prepared for optimum process condition. The dielectric constant and dielectric loss of Ba0.8Sr0.2TiO3 ceramics are 1681 and 0.0067 at 100 kHz in room temperature, respectively. The pyroelectric coefficient is 4542 μC·m−2·K−1. The mean detection rate (FD) reached 1.42 × 10−4 m3/2·J−1·F−1/2.

Ba0.7Sr0.3TiO3 (BST) thin films were deposited on Pt and SrRuO3(SRO)/Pt hybrid bottom electrodes by radio frequency magnetron sputtering. X-ray analysis indicated that both films were polycrystalline. Dielectric measurements showed that the films on SRO/Pt hybrid bottom electrode had lower dielectric constant and loss than the films on single Pt and the dielectric properties were frequency-independent. The leakage current density of Ba0.7Sr0.3TiO3 thin films on hybrid bottom electrode was also lower. Leakage mechanism investigations showed that the contact between the electrode-film interfaces of thin films on SRO/Pt hybrid bottom electrode was ohmic. Based on the results, the effects of SRO/Pt hybrid bottom electrode on the crystallization and electrical properties of BST thin films were discussed.

Amorphous GeSe2 film was prepared by the pulsed laser deposition technique and annealed at different temperature from 473 to 623 K. Using the ‘non-direct transition’ model proposed by Tauc, the short wavelength absorption edges of the films were well fitted and the optical band gaps ( E g opt ) were determined. The Tauc slope of the as-deposited film is smaller than those of annealed films, which were proposed as an indicator of the degree of structural randomness of amorphous semiconductors. The refractive index and thickness of the films were calculated from the optical transmission spectra using the Swanepoel method. The index of refraction decreased while E g opt increased gradually with increasing the annealing temperature. The thermal-bleaching and thermal-contraction effects were observed, which were interpreted as the reduction in the density of homopolar bonds according to the Raman spectra analysis and the diminution of porous structure in the fragments of the annealed films, respectively.

Barium strontium titanate (Ba1−x Sr x )TiO3 (BST) thin films were deposited on Pt, Ru, RuO2, and Pt/RuO2 electrodes by radio frequency magnetron sputtering. The interfacial structure characteristic of the BST films deposited on various electrodes was investigated. X-ray photoelectron spectroscopy investigations showed that the interfacial diffusion layer in BST/Pt and BST/Ru are approximately 6 and 10 nm, respectively. The BST films are short of Ba and O elements comparing with the stoichiometry Ba0.65Sr0.35TiO3 in the interface region. Dielectric measurement of the BST films with thickness ranging from 70 to 400 nm revealed that the BST films deposited on Pt and Pt/RuO2 bottom electrodes have similar dielectric property, the BST films deposited on Ru have the highest bulk dielectric constant, and the thickness dependence of dielectric constant on the BST film deposited on RuO2 electrode can be neglected. The interfacial layer dielectric constant of BST films deposited on Pt and Ru electrodes are estimated to be about 34.5 and 157.1, respectively. The effect of interfacial dead-layer on the dielectric constant could be eliminated through selecting appropriate bottom electrodes.

Ba0.65Sr0.35TiO3 (BST) thin films were deposited on Pt/Ti/SiO2/Si substrates by radio frequency magnetron sputtering technique. X-ray photoelectron spectroscopy (XPS) depth profiling data show that each element component of the BST film possesses a uniform distribution from the outermost surface to subsurface, but obvious Ti-rich is present to BST/Pt interface because Ti4+ cations are partially reduced to form amorphous oxides such as TiOx (x

The influence of lattice strain on the strength of dipoles in the Ho3+-doped barium-strontium titanate (BST) thin films has been analyzed. Thin films were produced by using the sol–gel technique on Si substrate. The resulting stress due to fabrication process was quantified by analyzing the {200} planes of the cubic perovskite structure and comparing them with the data for bulk materials. The influence of strain and changes due to Ho3+-ion doping were characterized by Raman and visible photoluminescence spectroscopy, which clearly show the evidence for the increased tetragonality due to weaker dipole interaction at B-sites of cubic perovskite in the presence of Ho3+-ions at concentrations larger than 3 mol%. The film strain can therefore be controlled to enhance the intensity of emitted light at 650 nm.

Ba 0.65 Sr 0.35 TiO 3 (BST) thin films doped with Ho 3+ were prepared on silicon substrates by a modified sol–gel technique. The microstructure of the BST films was characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. The results showed that 3 mol% Ho-doped BST has the largest grain size and surface root-mean square roughness. The thickness of the film was about 1.36 μm. The Ho 3+ luminescence intensity reached a maximum value in the sample with 3 mol% Ho 3+ ions concentration sintered at 700 °C. All the results showed that the BST: Ho 3+ films may have potential use for photonic devices.

Sol-gel-derived Ba"0"."6"5Sr"0"."3"5TiO"3 (BST) thin films were etched in CF"4/Ar/O"2 plasma using magnetically enhanced reactive ion etching technology. The maximum etch rate of BST film is 8.47nm/min when CF"4/Ar/O"2 gas mixing ratio is equal to 9/36/5. X-ray photoelectron spectroscopy analysis indicates the accumulation of fluorine-containing by-products on the etched surface due to their poor volatility, resulting in (Ba,Sr)-rich and (Ti,O)-deficient etched surface. Compared to the unetched counterparts, the etched Ba 3d"5"/"2, Ba 3d"3"/"2, Sr 3d"5"/"2, Sr 3d"3"/"2, Ti 2p"3"/"2, Ti 2p"1"/"2 and O 1s photoelectron peaks shift towards higher binding energy regions by amounts of 1.31, 1.30, 0.60, 0.79, 0.09, 0.46 and 0.50eV, respectively. X-ray diffraction (XRD) analysis reveals that intensities of the etched BST (100), (110), (200) and (211) peaks are lowered and broadened. Raman spectra confirm that the Raman peaks of the etched film shift towards lower wave number regions with the values of 7, 6, 4 and 4cm^-^1, and the corresponding phonon lifetimes are longer than those of the unetched film because of the plasma-induced damage. When the etched films are postannealed at 650^oC for 20min under an O"2 ambience, the chemical shifts of Ba 3d, Sr 3d, Ti 2p and O 1s peaks, the variations for atomic concentrations of Ba, Sr, Ti and O, and the Raman redshifts are reduced, while the corresponding XRD peak intensities increase. It is conceivable that the plasma-induced damage of the etched film could be partially recovered during the postannealing process.

BaxSr1−xTiO3 (BST) thin films were grown on different substrates with or without LaNiO3 (LNO) layer by a modified sol–gel process. The BST thin films obtained have full perovskite phase with dense and crack-free surface. BST thin films on different substrates with LNO layer show (100) preferential orientation, the texture coefficient (TC) value is calculated to be about 42.7%, whereas those without LNO layer show a fairly reduced preferential orientation, the TC value is just about 24.8%. It is considered that the preferential orientation is induced by the interface stress between LNO and BST. Electrical property measurements showed that BST thin film with a LNO interlayer has lower capacitance and larger dielectric loss, which is due to smaller grains of the thin film.

Ba"0"."6"5Sr"0"."3"5TiO"3 (BST) thin films doped with holmium were prepared on silicon and fused quartz substrates by a modified sol-gel technique. The microstructures of BST films were characterized by atomic force microscopy (AFM) and X-ray diffraction (XRD). The results showed that 3mol% Ho-doped BST has the largest grain size and surface root-mean square roughness. The transmission spectra of Ho-doped BST films were measured by spectrophotometer. The refractive index and thickness of 1mol% Ho-doped BST film was calculated using envelope method from the transmission spectra. It showed that the refractive index increased from 1.94 to 2.09 as wavelength decreased from 700nm to 400nm, which was smaller than pure BST thin films we have reported. The average oscillator strength and wavelength were estimated using a Sellmeir-type dispersion equation. These results show the potential of using Ho-doped BST thin films as an electro-optical novel material.