Sustainable one-step synthesis of rare-earth-doped carbon quantum dots from agro-industrial and electronic waste precursors

The key scientific question addressed in this study is whether an agro-industrial biomass precursor and a real electronic-waste-derived rare-earth source can be coupled in a single hydrothermal process to produce carbon quantum dots (CQDs) with preserved carbon-core structure and tunable optical/magnetic properties. A one-step, waste-based hydrothermal synthesis of CQDs directly from cherry-seed biomass and spent fluorescent-lamp phosphor powder is reported, achieving in situ modification with rare-earth elements (REEs). The method simultaneously enables carbonization, nanoparticle formation, and REE coordination without multi-stage post-functionalization Structural and morphological characterization by HR-TEM reveals small graphitic domains (~2–4 nm) preserved upon REE modification. XPS and EDX provide evidence for surface-associated REE species, particularly Dy- and Ho-containing environments, coordinated to oxygen- and nitrogen-containing functional groups. Carbon K-edge XAS analysis indicates that the CQDs preserve a stable sp 2 -dominated carbon framework, with structural features governed primarily by surface-localized oxygen-containing functional groups. FT-IR and UV–Vis spectroscopy indicate changes in the surface ligand environment and the emergence of subtle metal-related electronic states. Photoluminescence studies demonstrate tunable emission: undoped CQDs blue-shift upon dialysis (λₑₘ ≈ 440 nm), whereas REE-doped show red-shifted emission (λₑₘ ≈ 500 nm) and enhanced radiative pathways via metal-ligand charge transfer. Magnetic measurements reveal a three-fold increase in paramagnetic responsiveness in REE-doped CQDs compared to undoped counterparts. These findings establish a sustainable, facile route to multifunctional CQDs with combined optical and magnetic properties, highlighting their potential relevance for future imaging-related applications, provided that cytotoxicity, colloidal stability in biological media, and REE ion-leakage are systematically evaluated.