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Accompanied by internal defect evolution in the perovskite lattice, the naturally formed “hollow” defects and obviously blue-shifted emission of CsEuCl3 nanocrystals were observed.

Mn4+-activated phosphors have become a hotspot in the development of inorganic red phosphors due to the fascinating photoluminescent properties. Herein, the synergetic manipulation of the flux effect and charge compensation was employed to improve the performance of Mn4+-activated CaAl12O19 red phosphors. The crystallinity was improved by appropriate Zn2+-doping, while nonradiative transition between Mn4+ ions is reduced by charge compensation of the formation of Mn4+–Mg2+ pairs with Mg2+ dopants. Thus, the emission of Mn4+-activated CaAl12O19 red phosphors has been remarkably enhanced. The low probability of nonradiative transition between Mn4+ ions was demonstrated by the thermal stability analysis. To depict the luminescent process, the crystal-field strength (Dq), and Racah parameters (B and C) were calculated to determine the sequence of the energy levels. Meanwhile, the warm WLEDs with high CRI and low CCT were obtained using the prepared phosphors as red-emitting composition. Our results clearly suggested that the synergetic strategy by combining the flux effect and charge compensation is an effective method to enhance the luminescence of CaAl12O19:Mn4+, and CaAl12O19:Mn4+/Zn2+/Mg2+ red-emitting phosphors, which have potential application value in warm WLEDs.

In this work, a dual p-n heterojunction of Cu2O/Ni(OH)2/TiO2 with type-II band alignment and matched build-in electric field was fabricated. This dual p-n heterojunction promoted the separation and transfer of charge carriers, which is much more efficient than individual p-n heterojunction. Photocatalytic hydrogen evolution under the simulated sunlight shows a high rate of 6145 μmol g−1 h−1 for Cu2O/Ni(OH)2/TiO2, which is 1.9 and 2.7 times that of Ni(OH)2/TiO2 and Cu2O/TiO2, respectively. The apparent quantum yield of Cu2O/Ni(OH)2/TiO2 is about 20.2% under the irradiation of monochromatic light (λ = 420 nm). The recycling test of hydrogen evolution also verified a high stability for this dual heterojunction. The type-II band alignment and matched build-in electric field was confirmed, which accelerate the migration of charge carriers. The width of space-charge layer was calculated and proved that the p-n junctions in Cu2O/Ni(OH)2/TiO2 are fully-depleted, which largely reduced the bulk recombination of charge carriers. The synergistic effect of the improved visible-light response, type-II band alignment, matched build-in electric field, and fully-depleted space-charge layer contributes to the enhanced photocatalytic hydrogen evolution.

Intergrowth ceramic series Bi4Ti3O12/Bi4.5Na0.5Ti4O15 have been prepared through solid state reaction. X-ray diffraction analysis shows the coexistence of Bi4Ti3O12 and Bi4.5Na0.5Ti4O15 phases with slight lattice distortion. Scanning electron micrographs present the growth of grains and grain boundaries with different contents of Bi4.5Na0.5Ti4O15. The relaxation dielectric properties of the ceramics have been observed. The room-temperature dielectric constant at 100 Hz is initially increased and then decreased with the increase of Bi4.5Na0.5Ti4O15. The impedance spectroscopy and the electrical modulus are also measured for explaining the dielectric behavior. The Nyquist plots display different semicircle arcs at 300 and 600 K. The imaginary part of electrical modulus has two peaks in the range of the measuring temperature. They prove the common influence of grains and grain boundaries on the dielectric properties. For further fitting the experimental data by Arrhenius theory, activation energy is obtained for grains and grain boundaries. Finally, the relaxor dielectric properties are attributed to the competition mechanism from the different growth situation of grains and grain boundaries with increasing Bi4.5Na0.5Ti4O15. Therefore, this kind of ceramics ought to be promising candidates for multifunctional device applications.

Synergistic the modulation of photon absorption capability and interfacial charge transfer of the photocatalyst are highly required for developing high-performance heterojunction photocatalysts. The ternary CdS-graphene quantum dots-titanate nanotubes (CdS-GQDs-TNTs) nanocomposite have been prepared by an in situ growth method. The physicochemical characterization reveals that the GQDs are firmly decorated on both inner and outer surface of TNT through the formation of Ti–O–C chemical bonding, and CdS QDs are loaded on the outer surface of TNTs through strong interfacial interaction. The intimate integrated CdS-GQDs-TNTs nanocomposite exhibits much superior photocatalytic performance toward H2 production compared with binary GQDs-TNTs and pure TNTs photocatalyst, which can be attributed to the combined interaction of the stronger visible light harvesting, the longer lifetime of photogenerated electron−hole pairs, faster interfacial charge transfer rate, fast and long-distance electron transport pass. The interfacial charge transfer mechanism of CdS-GQDs-TNTs ternary composite are proposed based on photoelectrochemical measurements.

Crystal structure, morphology, magnetic, and dielectric properties of (1 − x)Bi2Fe4O9–xMgFe2O4 bicomponent ceramics are investigated in detail. The material has been synthesized via sol–gel method. Analysis of X-ray diffraction data of the bicomponent ceramics shows the coexistence of orthorhombic Bi2Fe4O9 and spinel MgFe2O4 phases with no third phase. Microstructural and surface morphology displays the homogeneous grain distribution with different grain sizes of Bi2Fe4O9 and MgFe2O4. The magnetic measurement shows decreasing coercivity and increasing values of remnant and saturation magnetization with the increase in MgFe2O4. Temperature-dependent dielectric properties and electrical modulus are conducted in the temperature range of 27–527 °C with the frequency ranging from 1 to 30 kHz. Two abnormal peaks are, respectively, observed at low and high temperature ranges. The variation of electric properties is closely related to the composition of MgFe2O4. The results of dielectric and electrical modulus indicate the appearance of dielectric relaxation in (1 − x)Bi2Fe4O9–xMgFe2O4. Combined with the study of activation energy, the dielectric relaxation is mainly induced by different electric responses of various charge carriers intrinsically dominating in a thermally activated process with the incorporation of MgFe2O4. The combination of Bi2Fe4O9 and MgFe2O4 enhances the coexistence of magnetic and electric properties in the present composites. It is quite promising from application point of view.

Epitaxial PbTiO3 films with a smooth and dense surface were fabricated by a promising hydrothermal synthesis on an Nb:SrTiO3(100) substrate. The resulting coated substrate was used to fabricate a Pt/PbTiO3/Nb:SrTiO3 heterostructure device. The device exhibited a multilevel storage capacity with an appropriate R OFF / R ON ratio and excellent endurance and retention. An electric conduction analysis indicated that the resistive switching behavior of the device was attributed to the trap controlled space-charge-limited current conduction that was caused by the oxygen vacancies in the PbTiO3 hydrothermal films. The modulation of the Pt/PbTiO3 Schottky-like junction depletion under an applied electric field is thought to be responsible for the resistive switching behavior of the device in the carrier injection-trapped/detrapped process.

The large number of energy levels available to lanthanide ions makes the emission mechanism of lanthanide-doped luminescent materials extremely complicated. Herein, we focus on the discussion and analysis of luminescence manipulation in Gd2O3:Yb3+/Er3+ nanocrystals and systematically investigate ion-ion interaction–induced energy transfer in up- and downconversion processes to shed light on the manipulation mechanism, showing that the luminescence of the above nanocrystals can be controlled by varying the content of Yb3+. Based on Dexter's energy transfer theory and the fact that excitation of Er3+ ions results in the appearance of emission attributed to the 2F5/2→2F7/2 transition of Yb3+ in the near-infrared region (950–1100 nm), this behavior is ascribed to the occurrence of energy transfer from Er3+ to Yb3+.

Tailoring the band gap and understanding the underlying mechanism are important for extending the applications of graphene quantum dots in optoelectronics. In this work, we synthesize fluorinated graphene oxide quantum dots (F-GOQDs) through a photochemical method, and study their optical properties. The obtained F-GOQDs exhibit a maximal blue-shift of photoluminescence (PL) emission of ca. 77 nm compared to that of the graphene oxide quantum dots (GOQDs). The PL shift results from the substitution of the hydroxyls and carbonyls groups with fluorine during the fluorination process, which can tune the band gap of the GOQDs. Density functional theory (DFT) calculations support our proposed mechanism for band gap tuning in the GOQDs through the use of fluorination.

Light-modulated lead-free perovskites-based memristors, combining photoresponse and memory, are promising as multifunctional devices. In this work, lead-free double perovskite Cs2AgBiBr6 films with dense surfaces and uniform grains were prepared by the low-temperature sol-gel method on indium tin oxide (ITO) substrates. A memory device based on a lead-free double perovskite Cs2AgBiBr6 film, Pt/Cs2AgBiBr6/ITO/glass, presents obvious bipolar resistive switching behavior. The ROFF/RON ratio under 445 nm wavelength light illumination is ~100 times greater than that in darkness. A long retention capability (&gt, 2400 s) and cycle-to-cycle consistency (&gt, 500 times) were observed in this device under light illumination. The resistive switching behavior is primarily attributed to the trap-controlled space-charge-limited current mechanism caused by bromine vacancies in the Cs2AgBiBr6 medium layer. Light modulates resistive states by regulating the condition of photo-generated carriers and changing the Schottky-like barrier of the Pt/Cs2AgBiBr6 interface under bias voltage sweeping.

High-quality CH3NH3PbI 3−xClx (MAPIC) films were prepared using potassium chloride (KCl) as an additive on indium tin oxide (ITO)-coated glass substrates using a simple one-step and low-temperature solution reaction. The Au/KCl-MAPIC/ITO/glass devices exhibited obvious multilevel resistive switching behavior, moderate endurance, and good retention performance. Electrical conduction analysis indicated that the resistive switching behavior of the KCl-doped MAPIC films was primarily attributed to the trap-controlled space-charge-limited current conduction that was caused by the iodine vacancies in the films. Moreover, the modulations of the barrier in the Au/KCl-MAPIC interface under bias voltages were thought to be responsible for the resistive switching in the carrier injection trapping/detrapping process.

Additional file 1 Supporting Information.

Correction for ‘Enhanced photoluminescence stability and internal defect evolution of the all-inorganic lead-free CsEuCl3 perovskite nanocrystals’ by Yalei Gao et al., Phys. Chem. Chem. Phys., 2022, 24, 18860–18867, https://doi.org/10.1039/D2CP01374F.

Materials with tunable photoluminescence (PL) are highly desirable. It can lead to important applications such as photodetectors, bio-imaging, and broadband modulators. In this work, nitrogen-doped graphene oxide quantum dots (NGOQDs) were synthesized by hydrothermal method. The microstructures as well as optical properties of NGOQDs were studied. The as-prepared NGOQDs present tunable PL and exhibit a maximal PL blue-shift of ca. 88 nm compared to that of the graphene oxide quantum dots (GOQDs). The observed PL blue-shift of the NGOQDs is attributed to the high content of pyridine-like and pyrrolic-like nitrogen atoms doping in the NGOQDs. Our proposed mechanism for the PL blue-shift of the NGOQDs is supported by density functional theory (DFT) calculations.

Highly efficient H2 production from water splitting has been achieved by N-doped titanate nanotubes (N-TNTs) decorated with graphene quantum dots (GQDs) in this work. In order to promote charge carrier transmission at the interface, a facile and environmentally friendly in situ growth method was employed to construct a strongly coupled N-TNT/GQD composite photocatalyst. The results revealed that N atoms were effectively doped into the crystal lattice of the TNTs in the form of both interstitial N and substitutional N, and the GQDs were decorated onto both the inner and outer surfaces of the N-TNTs through the formation of Ti-O-C chemical bonds. Photoelectrochemical measurements proved that, in N-TNT/GQD composite, N-doping can extend light response to the visible-light range, and the coupling with GQDs not only enhanced visible-light absorption, but also promoted interfacial charge carrier transfer. Due to the synergistic effect between N-doping and GQD coupling, the closely integrated N-TNT/GQD composite exhibits a much superior photocatalytic H2 production performance under UV-vis irradiation, being 2.1 times higher than that of pure TNTs.

A crystalline BiFeO 3 (BFO) heteroepitaxial film was produced by mild hydrothermal epitaxy on a Nb–SrTiO 3 (100) (NSTO) substrate. The resulting coated substrate was used to fabricate a Pt/BFO/NSTO heterostructure device. The device exhibits reversible bipolar resistive switching behavior. The resistance states can be reversibly switched among multiple levels, by changing the magnitude of the reset pulse voltage. This illustrates the devices potential in multilevel nonvolatile memory devices. The resistive switching behavior of the device is attributed to trap-controlled space-charge-limited current conduction, which is controlled by oxygen vacancies in the film. The modulation of the Pt/BFO Schottky-like junction depletion under an applied electric field is thought to be responsible for the resistance switching behavior of the device, in the carrier injection-trapped/detrapped process.

Epitaxial CaTiO3 films, with smooth and dense surface, were fabricated by the promising hydrothermal synthesis on the Nb:SrTiO3(001) substrate. The resulting coated substrates was used to prepare Pt/CaTiO3/Nb:SrTiO3 heterostructure devices. The devices present a bipolar resistive switching behavior. Both high and low resistance states have not obvious degradation within ∼3 h and 1000 cycles measurements, which demonstrates the devices possess excellent retention and endurance characteristics. The resistive switching behavior of the devices can be explained by the trap-controlled space charge limited current conduction mechanism. Moreover, the modulation of the Pt/CaTiO3 Schottky-like barrier under an applied electric field is also responsible for the switching behavior, in the carrier injection-trapped/detrapped process.

The magnetic anisotropy of epitaxial, high-index Fe(h0) films is investigated. The strength of the in-plane uniaxial magnetic anisotropy increases monotonically with the inclination angle between Fe(001) and Fe(h0l). This increase is demonstrated to be caused by the cubic magnetocrystalline anisotropy and not by surface- or interface-related effects. The magnetic anisotropy of epitaxial, high-index Fe(h0) films is investigated. The strength of the in-plane uniaxial magnetic anisotropy increases monotonically with the inclination angle phi between Fe(001) and Fe(h0l). This increase is demonstrated to be caused by the cubic magnetocrystalline anisotropy and not by surface- or interface-related effects. image

The bipolar resistive switching behavior in a device based on an crystalline iron-based organic-inorganic, perovskite-like material of (CH3NH3)2FeCl4 (MAFC), was examined and studied. Both high and low resistance states appeared to have no obvious degradation during a measurement period of 600 s with 400 cycles in a Ag/MAFC/Cu device, which also exhibited good thermal stability over a wide temperature range of 290 to 340 K. The conductivity-state switching behavior was derived from the competition between the ionic current within the MAFC and the Faradaic current that originated from oxidative reactions at the Ag/MAFC/Cu interface. A model explaining the oxidative reaction process was established to describe the symmetric resistive switching behavior in the Ag/MAFC/Cu cell. With an applied bias voltage sweeping, the oxidative layers passivated and dissipated at the Ag/MAFC/Cu interface that resulted in the competition between the induced current and the ionic current, and thus caused a symmetric resistance change. On the basis of this interfacial effect, the MAFC crystals can be used as memristor elements in devices for write-read-erase-rewrite process.

In this paper, a new type of hydrogen‐bonding‐directed layer‐by‐layer (LBL) ultrathin film with photosensitive cinnamoyl chromophores was prepared. It could induce uniform alignment of liquid crystals (LCs) after being irradiated by linearly polarised ultraviolet light (LPUVL). The hydrogen‐bonding‐directed formation of a photochromic multilayer film was achieved on the basis of an alternating assembly of poly(4‐vinylpyridine) (PVPy) and poly(4‐acryloyloxy)cinnamic acid (PCA). The assembly process was followed by UV–visible spectroscopy. The nature of the interaction between the two polymers was identified as a hydrogen bond through Fourier transform infrared spectroscopy. When the film was irradiated by LPUVL, the cinnamoyl units in the film underwent [2+2] cycloaddition along the electric vector direction of the LPUVL. The polarised UV–visible spectra proved that the film was anisotropic, and then the film could induce homogeneous alignment of nematic LCs. With the number increment of the bilayers, the ...

A novel strategy based on self‐assembly technology was devised for design of photosensitive material as a ferroelectric liquid crystal (FLC) alignment layer. This development offers new tools for the study and control at the molecular level of the interaction of FLCs with solid surfaces. The photoreactive material was self‐assembled to the substrate by covalent bond linkage due to a special chemical adsorption reaction. Through ester bond linkage, a cyano group with strong polarity was introduced to be terminus of the film. Under irradiation of linearly polarised ultraviolet light, an optically anisotropic self‐assembled film was easily obtained. The irradiated film was demonstrated to result in homogenous alignment of FLC by optical transmittance measurements and polarising optical microscopy images of a FLC cell at different rotation angles. The alignment quality of the FLC on this self‐assembled monolayer film is comparable to that of commercial rubbed polyimide film. Furthermore, it was also found tha...

A novel layer‐by‐layer (LBL) film containing dual photoreaction groups, cinnamoyl and azobenzene, was prepared from poly(diallyldimethylammonium chloride) (PDDA) and a photosensitive polyanion, PCAzo, in aqueous solution via electrostatic attraction. The film was able to induce uniform alignment of liquid crystals (LCs) with good stability and 2.3° pretilt angle by oblique irradiation with linearly polarised ultraviolet light (LPUVL). UV absorption and FTIR spectroscopic results indicate that the photoreactions of the two photoreactive groups jointly participate in generating the anisotropy of the film. The dichroic ratio of the film was found to depend on the number of adsorbed layers. The thicker film has the larger dichroic ratio after the LPUVL irradiation. The reorientation behaviour of the LC molecules was found to be associated with the LBL film thickness. Experiment results revealed that the photo‐crosslinking of the cinnamoyl groups was responsible for the stability of the anisotropic orientation...

A novel vertical alignment film for nematic liquid crystals is reported based on electrostatic self‐assembly of alkyl sulfonic salts in aqueous solution. A series of self‐assembled films with different alkyl chain lengths were prepared and used as alignment films. It was revealed that only when the number of carbon atoms in the alkyl chain approaches 11 or larger, could the self‐assembled film induce vertical alignment of liquid crystals. We also found that the homeotropic alignment of liquid crystals was related to the surface roughness of self‐assembled films. In addition, this vertical alignment film showed good electro‐optical characteristics and excellent thermal stability.

Photosensitive fluorinated polyesters (polymer‐n) of varying molecular mass M n (number‐average molecular mass) were synthesized. The thin films formed from polymer‐n samples could induce liquid crystal (LC) alignment after irradiation by linearly polarized ultraviolet light. The LC alignment direction on the irradiated films was investigated in detail by linearly polarized infrared spectroscopy and polarizing optical microscopy. It was found that LC alignment behaviour changed with change in the molecular mass of polymer‐n: irradiated films with lower or higher M n induced homeotropic or homogenous alignment, respectively. There was no clear morphological anisotropy in these aligned films, as observed by atomic force microscopy. The surface energies of the irradiated films were also measured using the indirect contact angle method, where both surface energy and its polar component increased with increasing M n. The variation in M n could be considered as a main reason for varying alignment behaviour.

In this paper, a new layer-by-layer (LBL) ultrathin film with photosensitive cinnamoyl chromophores was prepared. It could induce uniform alignment of liquid crystals (LC) after irradiated by linearly polarized ultraviolet (LPUV) light. First, a photosensitive polycation containing cinnamoyl side groups was synthesized. Then a layer-by-layer ultrathin film was prepared in an aqueous solution of the polycations and poly (sodium 4-styrenesulphonate). The spectra of UV–vis absorption and ellipsometric measurement showed that the LBL film was uniform and suitable for the photoalignment of LC. When the film was irradiated by LPUV light, the cinnamoyl units in the film underwent [2 + 2] cycloaddition along the electric vector direction of the LPUV light. The polarized UV–vis spectra also proved that the film was anisotropic, and then the film could induce the homogeneous alignment of nematic LC. With the number of bilayers increasing, the alignment effect of multilayer film became better, and the contrast ratio became higher.

A photoalignment film derived from photosensitive self-assembled monolayer with a p-phenylenediacrylate group is reported. The precursor film was prepared by self-assembled reaction of chemical adsorption, and then the film was irradiated by linearly polarized ultraviolet light. The photoalignment film induces nematic liquid crystal to align homogeneously, and the alignment direction of the liquid crystal molecules is perpendicular to the polarized direction of incident ultraviolet light. By variation of the length of the alkane chain and the different functional group at its terminus, the self-assembled photoalignment films with different polarity were prepared and determined. The film with n-alkyl benzene moieties showed better alignment performance than the others.

We report a novel epitaxial growth of EuTiO3 films on SrTiO3(001) substrate by hydrothermal method. The morphological, structural, chemical, and magnetic properties of these epitaxial EuTiO3 films were examined by scanning electron microscopy, transmission electron microscopy, high-resolution X-ray diffractometry, X-ray photoelectron spectroscopy, and superconducting quantum interference device magnetometry, respectively. As-grown EuTiO3 films with a perovskite structure were found to show an out-of-plane lattice shrinkage and room-temperature ferromagnetism, possibly resulting from an existence of Eu3+. Postannealing at 1,000°C could reduce the amount of Eu3+, relax the out-of-plane lattice shrinkage, and impact the magnetic properties of the films. PACS 81.10.Aj; 81.15.-z; 61.05.-a

Epitaxial LaFeO3-PbTiO3 (LFPTO) thin films were hydrothermally grown on the Nb-SrTiO3 (100) (NSTO) substrates with a thickness about 250 nm. As fabricated Pt/LFPTO/NSTO/Pt devices exhibit reversible bipolar resistive switching behavior. The resistance ratios between high resistance state and low resistance state exceed three orders of magnitude, which can be maintained over 6 h without observable degradation. It indicates that the Pt/LFPTO/NSTO/Pt devices reveal excellent data retention and endurance characteristics. The resistive switching mechanism of the device could be attributed to the trap-controlled space-charge-limited current conduction which is controlled by the localized oxygen vacancies in the films. Furthermore, variation of Pt/LFPTO Schottky junction depletion thickness and barriers height modulated by oxygen vacancies at Pt/LFPTO interface was suggested to be responsible for the resistance switching behaviors of the devices.

Layer-by-layer films have been fabricated from diazoresin (DR) and poly[4-sulfonyl phenoxy(4-acryloyloxy)cinnamate, sodium salt] (PACSS) in aqueous solution via electrostatic attraction. The ionic bonds between the diazonium ions and sulfonate ions in the film were converted into covalent bonds by irradiation with 365 nm UV light. It was also confirmed that the vinylene units of the cinnamoyl group in PACSS did not change in this process. Covalently attached self-assembled ultrathin films containing photosensitive cinnamoyl groups could align liquid crystals (LC) uniformly with good stability after irradiation with linearly polarized ultraviolet light (LPUVL). In this work, polarized UV-vis spectroscopy was utilized to investigate the photochemical process of the covalent film. It was found that cinnamoyl moieties parallel to the polarization direction of the LPUVL were consumed by the photoreaction faster than those perpendicular to the polarization direction. It can be concluded that the selective photoreaction induced the anisotropy of the films. Experimental results revealed that the degree of photoreaction and the dichroic ratio of the films depended on the number of adsorbed layers and the irradiation time. These results were correlated with the LC homogeneous alignment behavior in the parallel LC cell. The reorientation behavior of the LC molecules was found to be associated with the covalent film thickness and irradiation time.