Highly Efficient Light‐Emitting Diode of Graphene Quantum Dots Fabricated from Graphite Intercalation Compounds

Abstract

wileyonlinelibrary.comCOMMUNICATION electrochemical processing, [ 9 ] have been suggested to date. Despite some success in the synthesis of GQDs, these methods have limitations as well, such as the requirement of special equipment and extremely expensive raw materials, long fabrication times, low production yields, and the use of harmful chemical reagents. In this contxt, the method of oxidation and a further cutting reaction of graphite is appealing for the mass production of GQDs. [ 9,[11][12][13][17][18][19][20] However, numerous oxygenous functional groups and defects are inevitably generated both on the basal plain and at the edges of GQDs. This significantly infl uences the dispersion properties of GQDs and makes it diffi cult to control the emission wavelength of GQDs. [21][22][23][24] This oxidation of GQDs thwarts both fundamental understanding of the origin of luminescence and attempts to realize practical applications. In particular, the use of GQDs as an alternative to organic active materials for light-emitting diodes (LEDs) remains challenging due to low production yields and low quantum yields. The development of novel strategies to synthesize high-quality GQDs with controlled oxidation on a large scale is thus crucial.Herein, we suggest an easy and mass-producible route to obtain high-quality GQDs with controlled oxidation by graphite intercalation compounds (GICs). The proposed method is cost-effective and eco-friendly, as potassium-sodium tartrate (KNaC 4 H 4 O 6 ·4H 2 O) serves as both an intercalant into graphite and a solvent in the solvothermal reaction. After the formation of GICs, a dissolution process in water generates a large amount of GQDs (>60% yield) without requiring any surfactants or hazardous chemical solvents. More interestingly, in contrast to the visible emission of most GQDs synthesized from an oxidation method, our GQDs emit near the UV range (∼400 nm), which has been reported as the intrinsic emission wavelength of GQDs with low oxidation. [ 21,23,25 ] This result extends and confi rms our current understanding of the fl uorescence mechanisms of GQDs with respect to quantum confi nement effects, [26][27][28] recombination of localized electron-hole pairs, [ 8,18 ] triplet states from zigzag sites, [ 17 ] oxygenous emissive traps, [ 11 ] and intrinsic/extrinsic states. [ 25 ] We also found that the fl uorescence of GQDs originated from two overlapped spectral bands with intrinsic and extrinsic states and fi rst discovered the carrier transfer process from intrinsic to extrinsic states. Furthermore, the degree of oxygen content, which controls the fl uorescence color, was controlled simply by changing the sizes of the GQDs. These results were realized by preparing highquality GQDs with a narrowly distributed size via GICs.To confi rm the superior performance of these GQDs and suggest the possibility of optoelectronic applications, we With strong optical absorptivity and a widely tunable bandgap, graphene is an attractive material for optical and optoelectronic devices. [ 1,2 ...

Origin of White Electroluminescence in Graphene Quantum Dots Embedded Host/Guest Polymer Light Emitting Diodes

“…The PLED using GOQDs blended PVK as emissive layer exhibited a lower current density than that of the PLED using PVK as emissive layer owing to better charge balance achieved by GOQDs. The device performance of our simple structured PLED is relatively poor (maximum luminance is 1 cd/m 2 at 11 V) compared with reported results13. However, this simple structure of PLED is more suitable to reveal the origin of EL emission in PLEDs, which satisfies our research purpose.…”

“…Here, GQDs were synthesized by amidative cutting of tattered graphite (Ami-GQD). Jeon’s group also reported similar results using poly(9-vinylcarbazole (PVK) as host matrix13. In both cases, it is suspected that EL from GQDs originated from (1) electron and hole transfer from the host to GQDs, which were injected into the host from the electron and hole transporting layers; (2) direct electron and hole injection into GQDs from the electron and hole transporting layers; and (3) energy transfer from the host to GQDs guest.…”

The New Graphene Family Materials: Synthesis and Applications in Oxygen Reduction Reaction

“…Generally, the graphitic materials, such as carbon nanotubes (CNTs) [38,39], carbon fiber [40], grapheme oxide (GO) [41], grapheme [36], graphite [42] and other materials [43][44][45], are usually used as the carbon source to produce GQDs. Chemical acid oxidation [41,46,47], the electrochemical approach [38,48,49], the hydrothermal or solvothermal cutting method [50][51][52] and the physical method [53,54] are employed to synthesize GQDs.…”

Recent Advances in Graphene Quantum Dots as Bioimaging Probes

“…Generally, the approaches can be divided into two groups: top-down and bottom-up methods. In the top-down methods, GQDs are usually synthesized through the cleavage of relatively large bulk precursors, such as graphite [53][54][55], carbon black [56][57][58], coal [59][60][61], metal-organic framework (MOF) [40], 3D graphene [62], graphene oxide (GO) [63][64][65][66][67], carbon nanotubes [68][69][70], carbon fiber [53,[71][72][73] and C 60 [74,75] into small pieces of graphene sheets by chemical oxidation etching [76][77][78][79][80][81], electrochemical exfoliation [65,[82][83][84][85], Li/K intercalation [86,87], hydrothermal/solvothermal treatment [88][89][90][91][92][93][94], microwave irradiation [95...…”