Rhodamine B-Derived Low-Toxicity Full-Color Carbon Dots with Wide Tunable High-Stable Liquid-State Lasers

Carbon dots (CDs) serve as a novel, non-toxic, cost-effective, and highly-stable solution-processable nanolaser material. However, compared to commonly used commercial laser dyes, CDs exhibit lower photoluminescence quantum yields (PLQYs), radiation transition rates, and gain coefficients. Consequently, this leads to higher laser thresholds that significantly impede the expansion of practical applications for CDs. Therefore, enhancing the gain performance of CDs is crucial in guiding the design of CD gain materials and promoting their practical applications. Herein, Rhodamine B (RhB) is employed as a sole precursor for the synthesis of full-color CDs (FCDs) with vibrant blue, green, yellow, red, and NIR (denoted as B-CDs, G-CDs, Y-CDs, R-CDs, and NIR-CDs) fluorescence through cross-linking, polymerization, and carbonization processes. The photoluminescence (PL) spectra ranged from 434 to 703 nm. Notably, the PLQYs and gain performance of FCDs are improved due to cross-linked enhanced emission (CEE) effects. Green, yellow, red, and NIR laser emission is achieved with lower laser thresholds and exhibited superior laser stabilities than RhB. Furthermore, cytotoxicity tests confirm that FCDs possess significantly lower toxicity than RhB. This study not only validates the applicability of CEE in CDs for developing multicolor gain materials but also advances the practical application of miniaturized lasers based on CDs.