Kundu Subhro, Siddique Abu Bakar, González Irvin Fernando Guzmán, Mireles Kevin Armando Rodríguez, Valverde Maritza Iveth Pérez, Castillo Nicolás Antonio Ulloa, Reghunathan Madhusoodanan, Gutiérrez Domingo Ixcoatl García, Guerra Eduardo Martínez, Ray Mallar
School of Engineering and Sciences, Tecnológico de Monterrey, Monterrey, Nuevo León 64849, Mexico.
Universidad Autónoma de Nuevo León, Centro de Innovación, Investigación y Desarrollo en Ingeniería y Tecnología, Apodaca, 66600, Nuevo León, Mexico.
Nanoscale. 2025 Jul 31;17(30):17647-17657. doi: 10.1039/d5nr01811k.
Understanding the relationship between the local chemical structure and photoluminescence (PL) in graphene quantum dots (GQDs) and nitrogen-functionalized GQDs (N-GQDs) is critical for their advancement in optoelectronics, sensing, and bioimaging. Ensemble measurements mask the structural and functional heterogeneity intrinsic to these quasi-zero-dimensional systems. Here, we employed single-particle photo-induced force microscopy (PiFM) to chemically map individual GQDs and N-GQDs, revealing diverse surface functional groups and bonding architectures that are obscured in bulk analyses. PiFM-IR spectra correlate well with vibrational modes predicted by density functional theory (DFT) on model structures incorporating oxygen and nitrogen functionalities. While ensemble characterization techniques such as Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy support the findings of single-particle analysis, the latter offers significantly superior spatial and chemical resolution. Optical features of the GQDs and the N-GQDs show size- and chemical structure-dependent behaviour such as excitation-dependent emission thresholds and biexponential decay dynamics. These observations support a dual recombination mechanism involving band-edge-to-band-edge transitions and surface-/dopant-mediated transition pathways. By integrating these methods, we established a robust framework for connecting a structure with optical behaviour, highlighting the importance of single-particle studies for rational design of carbon-based quantum materials.
了解石墨烯量子点（GQDs）和氮功能化石墨烯量子点（N-GQDs）的局部化学结构与光致发光（PL）之间的关系，对于它们在光电子学、传感和生物成像领域的发展至关重要。总体测量掩盖了这些准零维系统固有的结构和功能异质性。在这里，我们采用单粒子光诱导力显微镜（PiFM）对单个GQDs和N-GQDs进行化学映射，揭示了在整体分析中被掩盖的各种表面官能团和键合结构。PiFM-IR光谱与在包含氧和氮官能团的模型结构上由密度泛函理论（DFT）预测的振动模式有很好的相关性。虽然拉曼光谱、X射线衍射和X射线光电子能谱等总体表征技术支持单粒子分析的结果，但后者提供了明显更优越的空间和化学分辨率。GQDs和N-GQDs的光学特性表现出尺寸和化学结构依赖性行为，如激发依赖的发射阈值和双指数衰减动力学。这些观察结果支持了一种双重复合机制，涉及带边到带边的跃迁以及表面/掺杂剂介导的跃迁途径。通过整合这些方法，我们建立了一个将结构与光学行为联系起来的强大框架，突出了单粒子研究对于合理设计碳基量子材料的重要性。
