Green Synthesis of Carbon Quantum Dots with Good Photoluminescence Properties from <i>Prosopis farcta</i> and Their Applications as Fe ³⁺ Ion Detectors and Optical Nanothermometers

Abstract Carbon quantum dots (CQDs) derived from biological sources have gained a great attention in healthcare and environmental applications, including biosensing bioimaging, electrocatalytic oxidation, and metal ion detection. In this study, for the first‐time, the fabrication of water‐soluble CQDs is reported using Prosopis farcta as a natural precursor via a one‐pot hydrothermal synthesis. The green‐synthesized CQDs were characterized in terms of their functional groups and morphology. Transmission electron microscopy (TEM) revealed an average particle size of 1.95 nm, while spectroscopic analysis confirmed a strong fluorescence emission with a quantum yield (QY) of 27.6%. The CQDs possess carbonaceous cores with surface functional groups and show a maximum green emission wavelength at 495 nm. Particularly, the characterized CQDs show excellent sensitivity toward Fe 3 ⁺ ions, leading to fluorescence quenching, enabling the development of a facile and efficient fluorescent sensing method for Fe 3 ⁺ detection. This sensor demonstrated a linear response in the range of 0.1–0.5 µM with a detection limit as low as 15 nM. Furthermore, the method was successfully adapted for the analysis of environmental water samples, achieving satisfactory recovery rates. This work introduces a novel, eco‐friendly approach to CQD synthesis from Prosopis farcta and presents a promising strategy for highly sensitive and selective Fe 3 ⁺ detection, with potential applications in optical nano‐thermometry and environmental monitoring.