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

Abstract 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 (Δλ = 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.