Surface Chemistry Routes to Modulate the Photoluminescence of Graphene Quantum Dots: From Fluorescence Mechanism to Up‐Conversion Bioimaging Applications

Abstract

The bandgap in graphene‐based materials can be tuned from 0 eV to that of benzene by changing size and/or surface chemistry, making it a rising carbon‐based fluorescent material. Here, the surface chemistry of small size graphene (graphene quantum dots, GQDs) is tuned programmably through modification or reduction and green luminescent GQDs are changed to blue luminescent GQDs. Several tools are employed to characterize the composition and morphology of resultants. More importantly, using this system, the luminescence mechanism (the competition between both the defect state emission and intrinsic state emission) is explored in detail. Experiments demonstrate that the chemical structure changes during modification or reduction suppresses non‐radiative recombination of localized electron‐hole pairs and/or enhances the integrity of surface π electron network. Therefore the intrinsic state emission plays a leading role, as opposed to defect state emission in GQDs. The results of time‐resolved measurements are consistent with the suggested PL mechanism. Up‐conversion PL of GQDs is successfully applied in near‐IR excitation for bioimaging.

Towards efficient photoinduced charge separation in carbon nanodots and TiO2 composites in the visible region

“…21 The long tail absorption band possibly arises from surface defect states. 24,25 The surface defects are unstable and dissipative in energy, which are unfavorable for efficient electron injection in PVs. 23,[26][27][28] In addition, the reported CDs are generally passivated with insulating long chain molecules, 10,12,29 which act as tunneling barriers and are against efficient electron injection and well performing CD-based optoelectronic devices.…”

Degradação rápida de folhas de policarbonato

“…Trabalhos sobre a atividade fotoluminescente de materiais a base de carbono, tais como dots de carbono excitados com radiação ultravioleta, relataram emissão dominante da região azul (5)(6)(7)(8) . A presença de elementos e grupos também infl uencia a atividade fotoluminescente.…”

“…A presença de elementos e grupos também infl uencia a atividade fotoluminescente. Cadeias alcalinas (-R-OH) ligadas a grafeno induzem a emissão na região azul (6) . Por outro lado, grupos amina, devido aos elétrons desemparelhados, induzem emissão na região vermelha (9) .…”

“…Apesar de a propriedade fotoluminescente ter sido relatada para materiais a base de carbono, como dots de carbono (5)(6)(7)(8)(9)(10) , não há estudos sobre a capacidade do PC de converter radiação ultravioleta em luz visível através da fotoluminescência. Também, ainda não há divulgação de estudos sobre os efeitos de névoa cáustica sobre o PC.…”

Preparation of carbon dot‐based ratiometric fluorescent probes for cellular imaging from Curcuma longa

“…[6] They possess novel properties including water solubility, high stability, biocompatibility, and high optical absorption efficiency with tunable emissions through efficient size dependent excitation. [7][8][9][10] Some reports cite problems when using FNPs such as instability, persistence in the body, and expense of availability. Therefore, exploring novel fluorescence probes to address these limitations and finding new available fluorescence tags as potential bioimaging probes is important.…”