Producing sustainable flame-retardant room temperature phosphorescent materials from natural wood assisted by borax

Materials exhibiting room temperature phosphorescence (RTP) and flame-retardant properties show great potential in a wide range of applications. However, such materials were rarely reported. Here, we found that the RTP of lignin is activated by borax. This is because borax forms non-covalent interaction with lignin, enhancing the spin-orbit coupling (SOC) and restricting the vibration of lignin. Encouraged by this result, borax was introduced into a wood matrix (B-wood) to activate the RTP of naturally occurring lignin in a wood matrix with a lifetime of ∼263.1 ms. Moreover, B-wood displays V-0-level flame retardant properties, the highest level in UL-94 standard (typical standard in evaluating flame retardant properties). As a demonstration of potential applications, B-wood was processed into multifunctional wooden materials and films, which simultaneously exhibit flame retardant properties and generate RTP emission.