Aniket Mukherjee, David Nečas, Lucie Janů, Jénnifer Gómez, Jan Michalička, Naděžda Pizúrová, Adrian Cernescu, Martina Janůšová, Lenka Zajíčková

Fluorescent Crystalline Carbon Quantum Dots Discovered in Amorphous Organic Films with Amino Groups

Advanced Materials (submitted)

Carbon quantum dots (CQDs), a class of photoluminescent nanoparticles, have a broad potential in biomedicine, photonics, and electronics owing to their biocompatibility and tunable optoelectronic properties. Here, we report the serendipitous discovery of crystalline CQDs with unique fluorescent behavior within otherwise amorphous amino-functionalized organic thin films, revealing a previously unknown pathway for CQD formation in low-temperature plasma polymerization of organic precursors. The CQDs are spherical, with diameters from 3 to 14 nm, and exhibit a graphitic crystalline structure with a lattice spacing of 0.335 nm. Due to their origin, the CQDs incorporate nitrogen and oxygen functionalities and are thus intrinsically heteroatom-doped. Analysis of optical properties proved dual-emission photoluminescence, comprising excitation-dependent and excitation-independent components. The excitation-dependent emission arises from the sp² graphitic core and its size-dependent quantum confinement, whereas the excitation-independent emission originates from discrete surface states associated with functional groups. Notably, the latter can be resolved into violet and ultraviolet emissions, the ultraviolet (3.88 eV) representing a distinct feature of these CQDs. Furthermore, molecular fluorophores are excluded as the source of the observed photoluminescence.

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