Enhanced Photoelectric Properties of CsPbBr3 by SiO2 and TiO2 Bilayer Heterostructures.

CsPbBr3/SiO2 heterostructures were synthesized by the hydrolysis reaction of a mixture of CsPbBr3 nanocrystals (NCs) and (3-aminopropyl)triethoxysilane (APTS) in air. Compared with CsPbBr3 NCs, the CsPbBr3/SiO2 heterostructures exhibit stronger photoluminescence (PL) intensity, longer lifetime of PL (∼40.5 ns), and higher PL-quantum yield (PLQY, ∼86%). The carrier dynamics of CsPbBr3/SiO2 was detected by the transient absorption (TA) spectrum. The experimental results show that SiO2 passivates the surface traps of CsPbBr3 NCs and enhances the PL intensity. However, photoelectrochemical impedance spectra (PEIS) demonstrate that the impedance of CsPbBr3/SiO2 is higher than that of CsPbBr3 NCs, which reduces carrier transport and extraction. Because the application of CsPbBr3/SiO2 in optoelectronics is limited, CsPbBr3/SiO2/TiO2 heterostructures were synthesized by the further reaction of tetrabutyl titanate (TBT). The TiO2 coating can reduce the impedance of the CsPbBr3/SiO2. Importantly, ∼68% of the PL intensity of CsPbBr3/SiO2 is retained. Compared with CsPbBr3/SiO2 and CsPbBr3 NCs, the CsPbBr3/SiO2/TiO2 demonstrates faster carrier transport (κct = 2.4 × 109 s-1) and higher photocurrent density (J = 76 nA cm-2). In addition, CsPbBr3/SiO2/TiO2 shows good stability under (ultraviolet) UV irradiation, along with water stability and thermal stability. Therefore, the double protection approach can enhance the stability of CsPbBr3 NCs and tune the optoelectronic properties of CsPbBr3 NCs.

Metal Halide Single Crystals RbCdCl3:Sn2+ and Rb3SnCl7 with Blue and White Emission Obtained via a Hydrothermal Process.

Until now, effective blue light-emitting materials are essentially needed for the creation of white light and precise color renderings in real-world applications, but the efficiency of blue light-emitting materials has lagged far behind. Here, we present a hydrothermal method to synthesize tin-based metal halide single crystals (RbCdCl3:Sn2+ and Rb3SnCl7). Two single crystal materials with different shapes and phases can simultaneously be synthesized in the same stoichiometric ratio. Rb3SnCl7 has a bulk shape, while RbCdCl3:Sn2+ has a needle shape. The deep blue emission (436 nm) of RbCdCl3:Sn2+ can be obtained under the optimal excitation wavelength irradiation. However, pure blue emission (460 nm) to white light can be obtained by changing the excitation wavelength in Rb3SnCl7. The refinement spectra of the electronic structures of RbCdCl3:Sn2+ and Rb3SnCl7 are investigated by density functional theory. It is concluded that the difference in the distribution of Cl energy states leads to the existence of Cl local defect states, which is the reason for the rich luminescence of the two single crystals. These findings provide a path for realizing single-phase broadband white-emitting materials.

Defective core-shell NiCo2S4/MnO2 nanocomposites for high performance solid-state hybrid supercapacitors.

The roles of oxygen vacancies to enhance the electrochemical performance were not clearly explained in comprehensive research. Herein, the vertically oriented NiCo2S4/MnO2 core-shell nanocomposites are in situ grown on the nickel foam (NF) surface and activated by oxygen vacancy engineering via a chemical reduction method. The scanning electron microscope (SEM) and transmission electron microscope (TEM) results show the shell-MnO2 is well coated on the core-NiCo2S4. The hierarchical core-shell nanostructures synergistically increase conductivity and provide rich faradaic redox chemical reactions. Moreover, the density functional theory (DFT) calculations further indicate that the electronic properties and structure properties in NiCo2S4/MnO2 electrode of reduction for 60 min (NiCo2S4/MnO2-60) are effectively adjusted by introducing oxygen vacancies. Impressively, the NiCo2S4/MnO2-60 electrode delivers substantially appreciable areal capacity of 2.13 mAh·cm-2 couple with superior rate capability. The as-prepared high-performance electrode material can assemble into solid-state hybrid supercapacitor. The fabricated NiCo2S4/MnO2-60//AC device exhibits an exceptional energy density of 43.16 Wh·kg-1 at a power density of 384.21 W·kg-1 and satisfactory cyclic stability of 92.1 % at current density of 10 mA·cm-2 after 10,000 cycles. In general, the work demonstrates the significance of NiCo2S4/MnO2-60 as a highly redox active electrode material for future practical application in supercapacitors.

Highly efficient yellow emission and abnormal thermal quenching in Mn2+-doped Rb4CdCl6.

In this paper, Mn2+-doped Rb4CdCl6 metal halide single crystals were prepared by a hydrothermal method. The Rb4CdCl6:Mn2+ metal halide exhibits yellow emission with photoluminescence quantum yields (PLQY) as high as 88%. Due to the thermally induced electron detrapping, Rb4CdCl6:Mn2+ also displays good anti-thermal quenching (ATQ) behavior with thermal quenching resistance (131% at 220 °C). The increase in the photoionization and the detrapping of the captured electrons from the shallow trap states were appropriately attributed to this exceptional phenomenon based on thermoluminescence (TL) analysis and density functional theory (DFT) calculations. The relationship between the fluorescence intensity ratio (FIR) of the material and temperature change was further explored using the temperature-dependent fluorescence spectrum. It was used as a temperature measuring probe based on absolute sensitivity (Sa) and relative sensitivity (Sb) with the change in temperature. The phosphor-converted white light emitting diodes (pc-WLEDs) were fabricated using a 460 nm blue chip with a yellow phosphor, which has a color rendering index (CRI = 83.5) and a low correlated color temperature (CCT = 3531 K). Because of this, finding new metal halides with ATQ behavior for high-power optoelectronic applications may be made possible by our findings.

Growth of SnX2 (X = Br, I) Single Crystals with Self-Trapped Exciton Emission.

Broadband emission with a large Stokes shift is important to obtain an excellent color rendering index of the solid-state lighting device. Among low-dimensional material and perovskite-like phosphors with broadband self-trapped emission, Sn-based phosphors have attracted much attention due to their high photoluminescence quantum yield (PLQY). However, the disadvantage is that the synthesis of Sn-based phosphors needs to be performed in a glovebox. Upon photoexcitation, the broadband emission of self-trapped excitons results from exciton-phonon coupling induced by the transient distortion of the lattice. Low-dimensional material structures often promote self-trapped emission because of more vibrational degrees of freedom and easier polarization under photoexcitation. Here, zero-dimensional (0D) SnX2 (X = Br, I) single crystals are synthesized by the solvent evaporation method in the air. SnX2 emits blue light, broadband yellow light, and deep red light, among which SnBr2 has the best luminescence performance. The photoluminescence quantum yield (PLQY) of SnBr2 reaches 85% and the Stokes shift reaches 265 nm. The PL intensity of SnX2 is linearly related to excitation power, which preliminarily indicates that the origin of SnX2 luminescence is attributed to self-trapped emission (STE). The white light-emitting diodes (WLEDs) were fabricated using yellow-emitting SnBr2 and blue-emitting BaMgAl10O17:Eu2+, which has a low correlated color temperature (3160 K) and a relatively common color rendering index (79).

Identification of the Intrinsic Dielectric Properties of Metal Single Atoms for Electromagnetic Wave Absorption.

Atomically dispersed metals on N-doped carbon supports (M-NxCs) have great potential applications in various fields. However, a precise understanding of the definitive relationship between the configuration of metal single atoms and the dielectric loss properties of M-NxCs at the atomic-level is still lacking. Herein, we report a general approach to synthesize a series of three-dimensional (3D) honeycomb-like M-NxC (M = Mn, Fe, Co, Cu, or Ni) containing metal single atoms. Experimental results indicate that 3D M-NxCs exhibit a greatly enhanced dielectric loss compared with that of the NC matrix. Theoretical calculations demonstrate that the density of states of the d orbitals near the Fermi level is significantly increased and additional electrical dipoles are induced due to the destruction of the symmetry of the local microstructure, which enhances conductive loss and dipolar polarization loss of 3D M-NxCs, respectively. Consequently, these 3D M-NxCs exhibit excellent electromagnetic wave absorption properties, outperforming the most commonly reported absorbers. This study systematically explains the mechanism of dielectric loss at the atomic level for the first time and is of significance to the rational design of high-efficiency electromagnetic wave absorbing materials containing metal single atoms.

Enhancing the stability of CsPbX3 (X = Br, I) through combination with Y-zeolites for WLED application.

The stability of perovskite quantum dots (PQDs) plays a vital role in practical devices. Besides silica coating, embedding PQDs in zeolites is another strategy to improve their stability significantly. Although the zeolite rigid framework has been reported to protect PQDs, there are few reports on the in situ synthesis of PQDs in zeolites. In this work, cubic phase CsPbX3 (X = Br, I) nanocrystals were successfully prepared by the ion exchange method combined with a non-polar organic trigger. Dropping a certain amount of ZnM2 (M = Br, I) solution into the intermediate product Cs4PbCl6 nanocrystals resulted in the formation of the final CsPbX3 nanocrystals. The ZnM2 solutions were prepared in non-polar solvents (hexane, octane, or chloroform). The highest photoluminescence quantum yield (PLQY) of the synthesized CsPbX3@zeolite composites can reach 83%, with a lifetime of 1.37 µs. The stability of the CsPbX3@zeolite composites thin film against damage from air and light is significantly improved. We fabricated white light-emitting diodes (WLEDs) using CsPbBr3@zeolite as the green light source and CsPbI3@zeolite as the red light source to further emphasize the practical application effect of the CsPbX3@zeolite composites. This work not only provides a new method for the synthesis of CsPbX3 nanocrystals but also involves the in situ synthesis of high stability CsPbX3@zeolite composites within the zeolite.

Tuning Dielectric Loss of SiO2@CNTs for Electromagnetic Wave Absorption.

We developed a simple method to fabricate SiO2-sphere-supported N-doped CNTs (NCNTs) for electromagnetic wave (EMW) absorption. EMW absorption was tuned by adsorption of the organic agent on the precursor of the catalysts. The experimental results show that the conductivity loss and polarization loss of the sample are improved. Meanwhile, the impedance matching characteristics can also be adjusted. When the matching thickness was only 1.5 mm, the optimal 3D structure shows excellent EMW absorption performance, which is better than most magnetic carbon matrix composites. Our current approach opens up an effective way to develop low-cost, high-performance EMW absorbers.

Mn2+/Mn4+ co-doped LaM1-xAl11-yO19 (M = Mg, Zn) luminescent materials: electronic structure, energy transfer and optical thermometric properties.

Dual-emitting manganese ion doped LaM1-xAl11-yO19 (M = Mg, Zn) phosphors were prepared by substituting Zn2+/Mg2+ with Mn2+ and replacing Al3+ with Mn4+. The LaM1-xAl11-yO19:xMn2+,yMn4+ phosphors show a narrow green emission band of the Mn2+ ions at 514 nm and a red emission band of the Mn4+ ions at 677 nm. In addition, the thermal stability of luminescence shows that the response of Mn2+ and Mn4+ to the temperature is obviously different in LaMAl11O19, implying the potential of the prepared phosphors as optical thermometers. The decay lifetime of Mn4+ was changed with temperature due to the different fluorescence intensity ratios of Mn2+ and Mn4+, and a dual-mode optical temperature-sensing mechanism was studied in the temperature range of -50-200 °C. The maximum relative sensitivities (Sr) are calculated as 3.22 and 3.13% K-1, respectively. The unique optical thermometric features demonstrate the application potential of LaMAl11O19:Mn2+,Mn4+ in optical thermometry.

Cr,Yb-codoped Ca2LaHf2Al3O12 garnet phosphor: electronic structure, broadband NIR emission and energy transfer properties.

The combination of a broadband near-infrared (NIR) phosphor and phosphor-converted light-emitting diodes (pc-LEDs) has proven to be an ideal choice for a high-efficiency NIR light source. Here, a garnet-type NIR Ca2LaHf2Al3O12:Cr3+ phosphor is obtained and its emission covered most of the NIR spectral range. Excited by 460 nm blue light, the maximum peak was located at 780 nm with a full width at half maximum (FWHM) of ∼141 nm and an internal quantum efficiency (IQE) of 33%. Moreover, the NIR spectra can be broadened by doping Yb3+ into the Ca2LaHf2Al3O12:Cr3+ garnet phosphor. A super broad FWHM of 300 nm and reduced thermal quenching were acquired, originating from the energy transfer of Cr3+→ Yb3+. The energy transfer process of Cr3+ and Yb3+ is described by means of an energy level diagram and time-resolved spectrum. Finally, a NIR pc-LED is fabricated by combining the Ca2LaHf2Al3O12:Cr3+,Yb3+ phosphor with blue chips, which has a photoelectric conversion efficiency of 10%. These results demonstrate the great potential of Ca2LaHf2Al3O12:Cr3+,Yb3+ in super broadband NIR pc-LED applications.

Large-Scale Synthesis of Three-Dimensional Reduced Graphene Oxide/Nitrogen-Doped Carbon Nanotube Heteronanostructures as Highly Efficient Electromagnetic Wave Absorbing Materials.

Herein, we use reduced graphene oxide as a substrate and NiFe as a catalyst to fabricate three-dimensional (3D) nitrogen-doped carbon nanotube (NCNT)/reduced graphene oxide heteronanostructures (3D NiFe/N-GCTs). The 3D NiFe/N-GCTs are composed of two-dimensional (2D) reduced graphene oxide-supported one-dimensional (1D) NiFe nanoparticle-encapsulated NCNT arrays. The NCNTs exhibit bamboo-like shapes with the length and diameter of 3-10 µm and 15-45 nm, respectively. Besides integration of advantages of 1D and 2D nanomaterials, the 3D NiFe/N-GCT heteronanostructure possesses interconnected network structures, sufficient interfaces, numerous defects, hundreds of void spaces enclosed by bamboo joints and the walls of the NCNT in an individual carbon nanotube, and large surface areas, which can improve their dielectric losses toward electromagnetic wave. Thus, the 3D NiFe/N-GCTs show satisfied property toward electromagnetic wave absorption. Typically, the optimized 3D NiFe/N-GCT displays excellent minimal reflection loss (-40.3 dB) and outstanding efficient absorption bandwidth (4.5 GHz), outperforming most of the reported absorbers. Remarkably, the synthesis of 3D NiFe/N-GCTs only involves vacuum freeze-drying and subsequent thermal treatment process at a high temperature, and thus, the large-scale production of 3D NiFe/N-GCTs can be achieved in each batch, affording the possibility of the practical applications of the 3D NiFe/N-GCTs.

Nanosecond passively Q-switched fibre laser using a NiS2 based saturable absorber.

Q-switched pulse laser generation is successfully demonstrated in both Erbium-doped fibre laser (EDFL) and Thulium-doped fibre laser (TDFL) cavities by employing Nickel disulfide (NiS2) as a saturable absorber (SA). Q-switched pulse laser operation at 1.55 µm and 2.0 µm is obtained at low pump power levels of 37 mW and 48 mW, respectively. For the EDFL, stable passively Q-switched laser output at a wavelength of 1561.86 nm is achieved, with a minimum pulse duration of 237 ns and a repetition rate of 243.9 kHz. For the TDFL, the centre wavelength of the laser output is 1915.5 nm, with a minimum pulse duration of 505 ns and a repetition rate of 214.68 kHz. NiS2 is used as SA for Q-switched laser generation over a broadband wavelength for the first time.

Nonlinear absorption and nonlinear refraction in a chemical vapor deposition-grown, ultrathin hexagonal boron nitride film.

An ultrathin hexagonal boron nitride film is synthesized by a method of chemical vapor deposition. Irradiated by femtosecond laser pulses in the visible spectrum of 400-800 nm, it exhibits multiphoton absorption and positive nonlinear refraction properties. The two-photon and three-photon absorption coefficients are of the order of 10-5 cm W-1 and 10-14 cm3 W-2, respectively. The nonlinear refraction coefficient is as large as ∼10-8 cm2 W-1. These nonlinear coefficients lead to figures of merit that meet the material requirements for all-optical switching devices.

Nonlinear absorption, nonlinear scattering, and optical limiting properties of MoS2-ZnO composite-based organic glasses.

MoS2-ZnO composites were synthesized using a solution-based method. The scanning electron microscopy and transmission electron microscopy analysis demonstrated that ZnO nanoparticles with a size of about 4.5 nm were coated on the basal surface of MoS2 nanosheets with an expanded spacing of the (002) plane. The MoS2-ZnO composite-based poly(methyl methacrylate) (PMMA) organic glasses (MoS2-ZnO-PMMA organic glasses) were prepared through a polymerization process. The nonlinear absorption (NLA), nonlinear scattering (NLS), and optical limiting (OL) properties of the MoS2-ZnO-PMMA organic glasses with different amounts of MoS2-ZnO were investigated using a modified Z-scan technique. Compared to MoS2-PMMA and ZnO-PMMA organic glasses, the MoS2-ZnO-PMMA organic glasses exhibited enhanced NLA, NLS, and OL properties, which were attributed to the interfacial charge transfer between MoS2 nanosheets and ZnO nanoparticles, the layered structure of MoS2 nanosheets, the small size effect of ZnO nanoparticles, and the local field effect. In addition, a changeover from saturable absorption (SA) to reverse saturable absorption (RSA) could be realized in the MoS2-ZnO-PMMA organic glasses by adjusting the input energy. The total nonlinear extinction coefficient and response time of the MoS2-ZnO-PMMA organic glasses could be up to 2380 cm GW(-1) and several hundred picoseconds, respectively. Compared to the MoS2 films, the MoS2-ZnO-PMMA organic glasses have higher optical damage threshold, better mechanical strength and flexibility. Thus the MoS2-ZnO-PMMA organic glasses are very promising for optical devices such as optical limiters, optical shutters, ultrafast lasers, and ultrafast optical switches.

Three-dimensional SiO2@Fe3O4 core/shell nanorod array/graphene architecture: synthesis and electromagnetic absorption properties.

We developed a new strategy, i.e., a seed-assisted method, to fabricate a three-dimensional (3D) SiO2@Fe3O4 core/shell nanorod array/graphene architecture. The fabrication processes involved deposition of ß-FeOOH seeds on the graphene surfaces in the ferric nitrate aqueous solution, subsequent growth of ß-FeOOH nanorod arrays on the graphene surfaces in the ferric chloride aqueous solution under hydrothermal conditions, deposition of SiO2 coating on the surfaces of ß-FeOOH nanorods, and final formation of the 3D architecture by a thermal treatment process. Scanning electron microscopy and transmission electron microscopy measurements showed that the SiO2@Fe3O4 core/shell nanorods with a length and diameter of about 60 and 25 nm, respectively, were almost grown perpendicularly on both side surfaces of graphene sheets. The measured electromagnetic parameters showed that the 3D architecture exhibited excellent electromagnetic wave absorption properties, i.e., more than 99% of electromagnetic wave energy could be attenuated by the 3D architecture with an addition amount of only 20 wt% in the paraffin matrix. In addition, the growth mechanism of the 3D architecture was proposed, and thus, the strategy presented here could be used as a typical method to synthesize other 3D magnetic graphene nanostructures for extending their application areas.

Enhanced reverse saturable absorption in graphene/Ag2S organic glasses.

G/Ag2S composites were synthesized for the first time by a hydrothermal method. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analysis demonstrated that Ag2S nanoparticles with a diameter of about 130 nm uniformly covered the graphene surfaces. G/Ag2S composites were dispersed in methyl methacrylate (MMA), polymerized at 75 °C for 30-35 min, and finally dried at 45 °C for 10 h, to afford G/Ag2S/PMMA organic glasses. The nonlinear absorption (NLA) properties of the G/Ag2S/PMMA organic glasses with different amounts of G/Ag2S were investigated by an open-aperture Z-scan technique. The experimental results showed that the G/Ag2S/PMMA organic glass with an appropriate amount of G/Ag2S exhibited enhanced reverse saturable absorption (RSA) properties compared to G/PMMA and Ag2S/PMMA organic glasses, which was attributed to the notable synergistic effects between graphene and Ag2S. Both one-photon absorption (OPA) in Ag2S and two-photon absorption (TPA) in graphene played important roles in RSA processes of the G/Ag2S/PMMA organic glasses. The effective NLA coefficient ßeff of the G/Ag2S/PMMA organic glasses was in the order of 10(3) cm GW(-1). Thus this kind of organic glasses have great promise in optical limiter and optical shutter applications.

Porous iron molybdate nanorods: in situ diffusion synthesis and low-temperature H2S gas sensing.

In the paper, we developed an in situ diffusion growth method to fabricate porous Fe2(MoO4)3 nanorods. The average diameter and the length of the porous nanorods were 200 nm and 1.2-4 µm, respectively. Moreover, many micropores existed along axial direction of the Fe2(MoO4)3 nanorods. In terms of nitrogen adsorption-desorption isotherms, calculated pore size was in the range of 4-115 nm, agreeing well with the transmission electron microscope observations. Because of the uniquely porous characteristics and catalytic ability at low temperatures, the porous Fe2(MoO4)3 nanorods exhibited very good H2S sensing properties, including high sensitivity at a low working temperature (80 °C), relatively fast response and recovery times, good selectivity, and long-term stability. Thus, the porous Fe2(MoO4)3 nanorods are very promising for the fabrication of high-performance H2S gas sensors. Furthermore, the strategy presented here could be expended as a general method to synthesize other hollow/porous-type transition metal molybdate nanostructures by rational designation in nanoscale.

Three-dimensional hierarchical architectures constructed by graphene/MoS2 nanoflake arrays and their rapid charging/discharging properties as lithium-ion battery anodes.

Charged up: Three-dimensional architectures constructed from graphene/MoS2 nanoflake arrays have been successfully fabricated by a one-step hydrothermal method. MoS2 nanoflakes with thicknesses less than 13 nm grow vertically on both sides of graphene sheets (see figure), which allows the architectures to be more stable during charging and discharging. Even at a high current density of 8000 mA g(-1), their discharge capacity is still up to 516 mA h g(-1).

Quaternary nanocomposites consisting of graphene, Fe3O4@Fe core@shell, and ZnO nanoparticles: synthesis and excellent electromagnetic absorption properties.

This paper presents for the first time a successful synthesis of quaternary nanocomposites consisting of graphene, Fe(3)O(4)@Fe core/shell nanopariticles, and ZnO nanoparticles. Transmission electron microscopy measurements show that the diameter of the Fe(3)O(4)@Fe core/shell nanoparitcles is about 18 nm, the Fe(3)O(4) shell's thickness is about 5 nm, and the diameter of ZnO nanoparticles is in range of 2-10 nm. The measured electromagnetic parameters show that the absorption bandwidth with reflection loss less than -20 dB is up to 7.3 GHz, and in the band range more than 99% of electromagnetic wave energy is attenuated. Moreover, the addition amount of the nanocomposites in the matrix is only 20 wt %. Therefore, the excellent electromagnetic absorption properties with lightweight and wide absorption frequency band are realized by the nanocomposites.

Fe2O3/TiO2 tube-like nanostructures: synthesis, structural transformation and the enhanced sensing properties.

The paper describes for the first time the successful synthesis of Fe(2)O(3)/TiO(2) tube-like nanostructures, in which TiO(2) shell is of quasi-single crystalline characteristic and its thickness can be controlled through adjusting the added amount of aqueous Ti(SO(4))(2) solution. The characterization of samples obtained at different stages using transmission electron microscope indicates that the outer TiO(2) shell is changed gradually from amorphous and polycrystalline phase into quasi-single crystal under thermal actions through the Ostwald ripening process, accompanying the corrosion of the central parts of Fe(2)O(3) nanorods, and the formation of small particles separating each other, leading to the special core/shell nanorods. Furthermore, Fe(2)O(3)/TiO(2) tube-like nanostructures can be transformed into Fe(2)TiO(5) nanostructures after they are thermally treated at higher temperatures. Those nanostructures exhibit enhanced ethanol sensing properties with respect to the monocomponent. Our results imply that not only hollow nanostructures, but also a novel type of nanostructures can be fabricated by the present method for nanodevices.