Self‐Assembled Organic Single‐Crystals Embedded with Dual‐Color Phosphorescent Carbon Dots for Aqueous RTP Materials

New types of aqueous room-temperature phosphorescent (RTP) materials have attracted significant attention due to their ability to resist quenching in aqueous and oxygen-containing environments. Herein, a novel aqueous RTP material, namely S-CDs@SA composite, is successfully prepared via a one-pot hydrothermal method, using sulfanilic acid (SA) as the precursor and cysteamine hydrochloride as the auxiliary agent to enhance the phosphorescence intensity. This material is composed of SA single crystals embedded with sulfur-doped carbon dots (S-CDs). Under 365 nm excitation, it shows blue fluorescence centered at 476 nm. After the excitation stops, strong phosphorescence appears at 586 nm along with a weak shoulder peak at 495 nm. The composite achieves a phosphorescence quantum yield of 9% with an afterglow lifetime of 827.5 ms, and its luminescence remains stable in aqueous environments. Notably, the phosphorescence color of the material shifts from yellow to green at both low (77 K) and high (388 K) temperatures, while the addition of a small amount of water can suppress the thermochromic effect at high temperatures. Owing to these unique phosphorescent characteristics, S-CDs@SA exhibits considerable potential for application in advanced information encryption technologies.