Adv. mater.: GQD @ BNO with high efficiency photoluminescence is used for AC powder electroluminescent display device

Graphene quantum dots (gqds) are one of the members of graphene family Because of their unique optical properties and good biocompatibility, they are widely concerned by scientists These excellent properties also make gqds become a substitute of semiconductor quantum dots (QDs), which are more toxic At present, many research groups have reported gqds based light-emitting diodes (gqds led s), whose preparation strategy is to introduce gqds into the active layer composed of organic main materials and gqds dopants However, compared with the most advanced QDs based light emitting diodes (qleds), the performance of these QDs LEDs is still poor, mainly due to the π - π interaction in the plane structure of the gqds, which leads to the serious aggregation of the gqds The aggregation of this solid-state gqds induces photon reabsorption and non radiative energy transfer, which leads to aggregation fluorescence quenching (ACQ) ACQ limits the maximum doping concentration of gqds in organic host, resulting in poor performance of GQD LEDs Gqds in powder state does not even emit fluorescence and can not be used as active materials of any solid LEDs Therefore, it is a challenging research topic to find an effective way to control the aggregation of gqds to reduce its ACQ effect The researchers reported a way to reduce the ACQ effect by dispersing gqds in the polymer matrix Although the steric hindrance of the polymer chain partially reduces the aggregation of gqds, due to the thick polymer coating, the pl-qy of the prepared material is low and not suitable for carrier injection Recently, Professor seokwoo Jeon of the Korean Academy of science and technology and his collaborators built gqds @ BNO, a high-efficiency photoluminescent material, into boron oxynitride (BNO) substrate by simple microwave-assisted method, and used it as the active material of AC powder electroluminescent (acpel) display devices This is the first acpel device based on gqds This achievement was published in advanced materials (DOI: 10.1002 / ADMA 201802951) under the title of "efficient solid state photoluminescence of graphite quantum dots embedded in boron oxynitride for AC electronic device" Firstly, GQD @ BNO (Figure 1a) was prepared by microwave-assisted heating, and then it was characterized Scanning electron microscope (SEM) images show that GQD @ BNO has irregular shape (Figure 1b) In addition, three gqds samples with different loading rates (R GQD) were analyzed by X-ray photoelectron spectroscopy (XPS) and C1s (Figure 1c) The results show that with the increase of R GQD from 0.06 wt% to 0.96 wt%, the C1s binding energy of C=O changes from 288.8 eV to 289.3 eV, which means that the amount of hydrogen bond between C=O on GQDs and -OH on the surface of BNO increases in the GQDs with higher loading rate In addition, the reliability of the above results was further confirmed by Fourier transform infrared (FT-IR) analysis (Figure 1D) of GQD @ BNO samples with different rgqds (source: adv mater.) then, the fluorescence properties of GQD @ BNO were studied (Figure 2) Compared with gqds aqueous solution, the fluorescence quantum yield of GQD @ BNO increased to 34.5% (Figure 2a) In addition, at 413 nm, the fluorescence intensity of GQD @ BNO is about 5.7 times higher than that of gqds aqueous solution, and the fluorescence of gqds powder is completely quenched due to photon self absorption and non radiation energy transfer between gqds aggregates However, between the emission wavelength of 270 nm and 310 nm, the fluorescence intensity of GQD @ BNO is lower than that of BNO (Figure 2b), which indicates that the fluorescence energy is transferred from BNO donor of wide band gap to gqds receptor of narrow band gap, thus promoting the pl-qy increase of GQD @ BNO (source: adv mater.) because GQD @ BNO has high-efficiency solid-state fluorescence characteristics, the author further verified the applicability of GQD @ BNO as an active material in acpel devices (Figure 4) Typical structures of acpel devices include top electrode / dielectric layer / light-emitting layer / dielectric layer / bottom electrode (Figure 4a) The electroluminescence mechanism of acpel devices based on gqds is shown in Figure 4C, which shows the influence of BNO substrate on the electroluminescence performance Due to the role of local dielectrics, BNO not only helps electrons to tunnel into the gqds through electrical excitation, but also prevents dielectric breakdown under high electric field, so as to achieve efficient electroluminescence (source: adv mater.) conclusion: by embedding gqds into BNO matrix, the author constructed GQD @ BNO with high efficiency photoluminescence and used it as the active material of acpel device The fluorescence quantum yield of gqds increased significantly with the addition of BNO matrix It is predicted that the performance of the device can be further improved and the quantum yield of fluorescence can be increased by designing wider gap matrix materials precisely.