Tetrapod-like ZnO (T-ZnO) nanostructures were synthesized by a simple vapor phase oxidation method without any catalysts or additives. We optimized the performances of T-ZnO nanostructures by adjusting the partial pressure of Zn vapour in the total pressure of the quartz chamber and obtained T-ZnO nanostructure materials of high purity, uniform morphology and size and high aspect ratio with a low turn-on electric field of 2.75 V μm−1, a large field enhancement factor of 3410 and good field emission stability for more than 70 hour continuous emission. Besides, based on the optimized T-ZnO, we developed metal grid mask-assisted water-based electrostatic spraying technology, and fabricated a large-scale, pollution-free, hole-shaped array T-ZnO nanostructure cathode used in a triode structure field emission planar light source. The controllable performances of the triode device were intensively investigated and the results showed that the triode device uniformly illuminated with a luminous intensity as high as 8000 cd m−2 under the conditions of 200 V grid voltage and 3300 V anode voltage. The research in this paper will benefit the development of a high performance planar light source based on T-ZnO nanostructures.

•Graphene quantum dots (GQDs) were synthesized from double walled carbon nanotubes.•The GQDs have uniform size distribution.•The fluorescent lifetime of GQDs is wavelength-dependent.•GQD–PMMA nanocomposite exhibits nonvolatile rewritable memory effect.•Flexible memory was realized based on the GQD-based nanocomposite.We presented a facile method to prepare graphene quantum dots (GQDs) from double-walled carbon nanotube with blue light emission in a chlorobenzene solution, which enabled the preparation of GQD–polymer hybrid nanocomposite. The wavelength-dependent fluorescent lifetime of the GQDs was investigated by using time-resolved photoluminescence technique. Significantly, nonvolatile rewritable memory effect was observed for the GQD-based nanocomposite, suggesting the promising applications of GQDs in data storage. Moreover, due to the easy solution process, we demonstrated the design and realization of flexible GQD-based memory device. This work may expand the application of GQDs to the portable electronic devices.Graphical abstract

•Graphene/Ag/Al-doped zinc oxide (AZO) multilayer films were fabricated.•The film can maintain high conductivity and transmittance during bending test.•The film was used as the anode to fabricate a green FOLED.•The FOLED exhibited a high flexibility and light-emitting stability upon bending.Graphene/Ag/Al-doped zinc oxide (AZO) multilayer films were fabricated by using chemical vapor deposition and magnetron sputtering methods. The electrical and optical properties of the transparent conductive graphene/Ag/AZO films were investigated. The graphene/Ag/AZO film can maintain high conductivity and transmittance without obvious degradation during bending test. A green flexible organic light emitting diode with a structure of graphene/Ag/AZO/N,N-diphenyl-N,N-bis(1-napthyl)-1,1-biphenyl-4,4-diamine/tris(8-hydroxyquinoline) aluminum(III)/lithium fluoride/Al exhibited a stable green emission and light-emitting efficiency during the cycle bending test. The multilayer films hold promise for application in flexible optoelectronic devices.Graphical abstract

A mechanical surface treatment is presented by using adhesive tape to modify the surface morphology of graphene cathodes and to improve their field emission properties. The treated graphene cathodes have numerous vertical sharp edges, which act as excellent field emission sites. Effectively improved field emission properties with low turn on field, low threshold field, high emission current density and high field enhancement factor are obtained due to the full utilization of the unique structure and excellent properties of graphene.•Mechanical surface treatment was used to modify the surface morphology of graphene.•Adhesive tape was used for mechanical surface treatment.•Efficient field emission of graphene film was obtained due to the post-treatment.•Low turn-on and threshold field can be obtained.•High emission current density and field enhancement factor can be achieved.

Vertical graphene field emission cathodes were fabricated using screen-printing and the following selective photoetching techniques. Excellent field emission properties of the screen-printed vertical graphene film were obtained with low turn on field, high maximum current density, and large field enhancement factor. The organic layer anchoring the vertical graphene sheets acted as negative feedback layer, which contributed to the high uniformity and stability of the field emission device. The results pave the low-cost way for applications of graphenes in large-scale field emission devices.Highlights► Vertical graphene field emission cathode was formed by screen-printing. ► Excellent field emission properties of the vertical graphene sheets were obtained. ► The organic layer anchoring the graphene sheets acted as negative feedback layer. ► The graphene-based field emission device has good emission stability.

Large scale zinc oxide (ZnO)-adhering patterned graphene cathodes were realized by using spin-coating technique, and their field emission characteristics were investigated. The graphene sheets edges are extracted from the hybrid cathode to form emission centers, leading to high field enhancement and low threshold field. The ZnO film improves the interface contact and adhesion of graphene sheets with the electrode and acts as negative feedback resistive layer, which contributes to the uniformity and long-time stability. Our study opens up avenues for application of graphene sheets in field emission device utilizing efficient, large scale, pattern and low-cost technology.Highlights► Large scale ZnO-adhering patterned graphene cathode was fabricated. ► Simple solution process was used. ► Excellent field emission can be achieved due to the extraction of graphene edges. ► The presence of ZnO film improves the uniformity and long-time stability.

Three-layer structured hybrid bistable devices (HBDs) utilizing graphene sheets sandwiched between polymer layers were fabricated by laminating two glass substrates coated with patterned electrodes and spacers. The hybrid devices using polystyrene (PS) and poly(vinyl-carbazole) (PVK) as matrix layer for graphene sheets demonstrated write-once-read-many-time and volatile memory effects, respectively. It is found that the memory properties of the HBDs can be tailored by varying the depth of the charge traps formed between the polymer matrix and graphene sheets. The possible operating mechanisms of the HBDs were analyzed based on the investigation of current–voltage characteristics for the hybrid devices.Graphical abstractHighlights► A tri-layer hybrid memory was fabricated by laminating two substrates with spacers. ► By using PVK as matrix for graphene sheets, the device exhibits WORM effect. ► The device shows volatile memory effect if graphene was sandwiched between PS layers. ► The behavior was due to various depth of traps formed between polymer and graphene.

Carbon nanotube (CNT)/Ag/Al-doped zinc oxide (AZO) multilayer films are fabricated on a plastic substrate by using spraying and magnetron sputtering methods at room temperature. The electrical and optical properties of the transparent conductive CNT/Ag/AZO films are investigated. The introduction of Ag and AZO layer can smoothen the surface, and improve the conductivity and optical transmittance of the multilayer films. The Ag thickness is optimized by estimating the figure of merit of the films. The CNT/Ag/AZO films can maintain high conductivity and transmittance without obvious degradation during repeated bending. The results indicate that the multilayer films have potential applications in flexible optoelectronic devices.Highlights► Carbon nanotube/Ag/Al-doped zinc oxide (AZO) multilayer films are fabricated. ► The introduction of Ag and AZO can improve conductivity and optical transmittance. ► Ag thickness is optimized according to figure of merit of the film. ► The films can maintain high conductivity and transmittance during bending tests.

Multilayer transparent electrode based on Al-doped zinc oxide (AZO)/Ag/Al-doped zinc oxide (AZO) was fabricated by sputtering, and a green organic light-emitting diode (OLED) device utilizing AZO/Ag/AZO as anode was fabricated. The AZO/Ag/AZO multilayer film exhibited superior square resistance and optical transmittance to those of commercial indium tin oxide (ITO). In comparison with the green OLEDs based on ITO and pure AZO anode, the green OLED based on AZO/Ag/AZO showed the highest light-emitting efficiency. The results indicate that AZO/Ag/AZO multilayer electrodes are a promising low-cost， low-toxic and low-temperature processing electrode scheme for OLED application.Highlights► AZO/Ag/AZO multilayer film was fabricated by sputtering. ► The film showed superior optical and electrical properties to those of ITO. ► Green OLEDs based on ITO, AZO, and AZO/Ag/AZO anodes were fabricated. ► The OLED with AZO/Ag/AZO anode exhibited the highest light-emitting efficiency.

White organic light-emitting diode (WOLED) with a structure of ITO/poly(N-vinylcarbazole) (PVK)/4,7-diphenyl-1, 10-phenanthroline (Bphen)/tris(8-hydroxyquinoline)aluminum (Alq3)/LiF/Al has been fabricated via the thermal evaporation technique. The electroluminescence (EL) spectrum of the as-fabricated WOLED covers from 380 to 700 nm of the visible light region with a wide blue emission from PVK and an interesting new red emission. The red emission at 613 nm in EL spectra of the WOLED was attributed to electroplex emission at PVK/Bphen interface since it was not observed in photoluminescence spectra. The WOLED showed a Commission International De l'Eclairage coordinate of (0.31, 0.32), which is very close to the standard white coordinate (0.33, 0.33).Highlights► A white organic light-emitting diode was fabricated by vacuum deposition. ► A new red emission at 613 nm was observed in the electroluminescence spectra. ► Red emission comes from electroplex instead of exciplex at PVK/Bphen interface. ► The device has a CIE coordinate of (0.31, 0.32).