Erbium‐Hyperdoped Silicon Quantum Dots: A Platform of Ratiometric Near‐Infrared Fluorescence

Ratiometric near-infrared (NIR) fluorescence holds great promise for important applications such as temperature sensing, food safety detection, and biological imaging owing to its self-calibration and contactless measurements in the NIR region. For ratiometric NIR fluorescence, the suppression of optical reabsorption and signal interference is crucial. In this work, freestanding erbium (Er)-hyperdoped silicon quantum dots (Si QDs) with UV absorption and NIR emission are synthesized via nonthermal plasma, effectively avoiding optical reabsorption. Er with the valence of +3 is found to be mainly located in the subsurface region of Er-hyperdoped Si QDs, which emit NIR light at the wavelengths of 830 and 1540 nm. The distinct difference between the two NIR wavelengths (Delta lambda = 710 nm) well impedes signal interference in ratiometric NIR fluorescence. It is shown that Er-hyperdoped Si QDs may be a powerful platform of ratiometric NIR fluorescence by exemplarily demonstrating their temperature-sensing capability in a wide temperature range (297-477 K) with high relative sensitivity (3.05% K-1), high-temperature resolution (<0.018 K), and high repeatability (>98%). The temperature sensing of Er-hyperdoped Si QDs may be further employed to construct logic gates, enabling in-sensor computing.