Simple synthesis of multifunctional N, S-doped carbon quantum dots for Cu2⁺ ion detection and luminescent applications

Abstract

This study successfully synthesized multifunctional nitrogen- and sulfur-doped carbon quantum dots (N, S-CQDs) using thiobenzamide and citric acid as precursors through a hydrothermal process under neutral conditions. The synthesized N, S-CQDs exhibited an average diameter of approximately 15 nm, which is notably larger than that of unmodified CQDs. Unlike conventional CQDs, the N, S-CQDs demonstrated stable yellow fluorescence that remained invariant under different excitation wavelengths. Furthermore, their surface functional groups endowed them with multifunctional luminescent properties. Specifically, these functional groups enhanced the sensitivity toward Cu²⁺, enabling the N, S-CQDs to exhibit a response to Cu²⁺ with extremely low detection limit (LOD) of 0.197684 and 0.149791, thus demonstrating excellent Cu²⁺ detection performance. Additionally, the N, S-CQDs displayed unique yellow luminescence with a quantum yield of 28.05%, rendering them a promising alternative to YAG: Ce³⁺ for applications in white light LEDs and fluorescent anti-counterfeiting labels. The fabricated simple WLED achieves an EQE of 32.39% with chromaticity coordinates of (0.3299, 0.2718). Given the simplicity and efficiency of the synthesis method, these N, S-CQDs hold significant potential for diverse applications across multiple fields.