Mechanism of photoluminescence properties of lyocell fibers changing with crystallinity

Although there have been sporadic reports that the crystallinity of cellulose has a significant impact on photoluminescence (PL) properties, the degree and pattern of this effect have not been thoroughly explored and elucidated. Here, we assume that crystallinity is positively correlated with PL emission. Then, lyocell fiber (CLY), a common man-made cellulose fiber, is selected to solve the above problems by exploring the PL emission properties of different crystallinity systems. Through the comparison of PL and persistent room temperature phosphorescence (p-RTP) emission properties under different crystallinity of CLYs, it is found that crystallinity is the key factor determining the above emission properties. The change trend of quantum yields is determined by the crystallinity. Through molecular interaction analysis and theoretical calculation, it is found that hexamers have more red shifted emission than tetramers, and to be more advantageous for phosphorescence emission. These interesting phenomena can be reasonably explained by clustering-triggered emission (CTE) and crystallization-Induced Phosphorescence (CIP) mechanism. Furthermore, these findings, in turn, offer more fundamental implications to the underlying mechanism of nonconventional chromophores. More meaningful is that these results can be used as a theoretical reference for real-time monitoring of CLY or other natural fiber in the actual mercerizing process.