Regulation And White Light Emitting Diode Application Of Full-color Fluorescent Graphene Quantum Dots

Fluorescent graphene quantum dots(GQDs)have attracted enormous scholarly attention due to their obvious advantages over conventional organic fluorophores and semiconductor quantum dots whose notable poor photostability,toxicity,and environmental hazards are well-documented.Their excellent properties including superior photostability and biocompatibility,simple and inexpensive synthesis,ease of surface modification,tunable excitation and emission properties make GQDs promising candidates for a vast variety of applications in energy conversion and storage devices,flexible devices,catalysis and biomedical fields,etc.The main research contents of this paper includes the following four parts:1.Full-color fluorescent GQDs were prepared in one-pot by regulating the electron withdrawing/electron-donating groups on the surface of GQDs with the acids.The highest quantum yield was as high as 72%.The increasing electron-withdrawing groups on the surface of GQDs originated from acid reagents boost their photoluminescence wavelength redshift and rise their particle sizes,elucidating the quantum size effect.These GQDs emit bright and remarkably stable full-color fluorescence ranging from blue to red light,and even white light.Full-color emissive polymer films and all types of high color rendering index WLEDs are synthesized by mixing multiple kinds of CQDs in appropriate ratios.And successfully applied full-spectrum fluorescent GQDs to white LED devices,and successfully regulated cold,standard and warm white LEDs.The success of the spectral tunability of GQDs will accelerate the development of carbon-based material systems with forward-looking optical phenomena.2.White luminescent GQDs(WGQDs)were prepared by using 1,5-diaminonaphthalene as the precursor and chloroform as the chlorine source and reacting in ethanol at 230 ~oC for 12 h.The modulation of chlorine doping amount and reaction temperature gives the WGQDs a single-crystalline structure and bright white fluorescence properties.In particular,the WGQDs also exhibit novel and robust white phosphorescence performance for the first time.An optimum fluorescence quantum yield of WGQDs is 34%,which exceeds the majority of reported WGQDs and other white luminescent materials.After a series of characterizations,it was found that this unique dual-mode optical characteristic of the WGQDs originates from the synergistic effect of low-defect and high chlorine-doping in WGQDs.Finally,it was successfully applied to the targeted fluorescent probe of the autonomous cell nucleus,and it can be excited and imaged at the wavelength of 633 nm.Secondly,it was successfully compounded on the purple chip to modulate the warm white light device LED.Finally,due to its excellent phosphorescence effect,it is successfully used in information anti-counterfeiting3.We introduce a simple,super-fast and scalable strategy that obtains GQDs within three minutes under microwave irradiation(MA-GQDs).The MA-GQDs exhibit excellent fluorescence quantum yields up to 35%in the optimum reaction condition.The MA-GQDs with single-crystalline and few-layers structure can reach the visible region with the longest absorption wavelength at 700 nm.Moreover,these ultra-bright fluorescence and stability MA-GQDs as phosphor and fluorescence probe could be efficiently applied in white light-emitting diodes and cell-imaging fields.The developed pathway to GQDs can provide unambiguous and remarkable insights into the design of high-fluorescence and few-defect GQDs,and expedite the applications of GQDs.4.Fluorescent probes with superior two-photon fluorescence are highly attractive in the field of bioimaging.Herein,we report a one-pot hydrothermal route to synthesis amine,sulfo cofunctionalized GQDs,which acts as efficient one-photon and two-photon fluorescent probes for cellular imaging.As synthesized GQDs exhibit ultrastability due to the edge-site functionalization of amine and sulfo groups.In addition,GQDs display attractive two-photon fluorescence properties.The two-photon absorption cross section of GQDs reaches up to 31,000 GM,which substantially exceeds that of the majority of traditional fluorescent materials.Furthermore,the noncytotoxicity GQDs exhibit a negligible photothermal effect under 808 nm femtosecond laser irradiation,which is suitable for long-term two-photon imaging and observation.These findings open new possibilities for using two-photon fluorescent GQDs in various biological applications.