Engineering of the luminescent properties for graphene quantum dots (GQDs) presents two enormous challenges: 1) The bandgap of GQDs is mainly determined by structural defects (size, shape, and the fraction of sp² and sp³ domains), which results in non-stoichiometric nature; 2) the preparation methods limit the achievement of an accurate chemical structure of GQDs, leading to many controversial explanations over the relationship between the structural defects and bandgaps. Here, single-layered GQDs with an exact structure are obtained by in-situ reaction of intercalated precursors in the confined nanospace of layered double hydroxides (LDHs). Subsequently, the structure-property relationship is uncovered, demonstrating the enhanced fluorescence and activated room temperature phosphorescence of the as-prepared GQDs-LDHs, which originate from synergistic effects: 1) strong confinement provided by the nanospace of LDHs; 2) rich O-containing functional groups on the surface of GQDs resulting from LDH catalysis. Moreover, the colorless nature and dual-emission characteristics of GQDs-LDHs satisfy the preconditions as anti-counterfeiting markers for protecting valuable documents (bank notes, commercial invoices, etc.). Particularly, owing to the low toxicity of GQDs and the edible property of LDHs, the GQDs-LDHs/gelatin capsules could be the new generation of potential green anti-counterfeiting material in the field of food and drugs.

中文翻译：

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受限纳米空间中单层石墨烯量子点的双模发射：防伪和传感器应用

石墨烯量子点（GQD）发光特性的工程设计面临两个巨大挑战：1）GQD的带隙主要由结构缺陷（sp ²和sp ³域的大小，形状以及分数）决定，这导致了化学计量性质；2）制备方法限制了GQD精确化学结构的实现，导致关于结构缺陷和带隙之间关系的许多有争议的解释。在这里，通过原位获得具有精确结构的单层GQD层状双氢氧化物（LDHs）的受限纳米空间中嵌入前体的反应。随后，发现了结构-性质关系，证明了所制备的GQDs-LDHs具有增强的荧光和活化的室温磷光，其起协同作用：1）LDHs纳米空间提供的强约束作用；2）由LDH催化产生的GQD表面富含O的官能团。此外，GQDs-LDH的无色性质和双重发射特性满足了作为保护贵重文件（钞票，商业发票等）的防伪标记的先决条件。特别是由于GQD的低毒性和LDH的可食用性，