Regulating trap distribution to achieve high-contrast mechanoluminescence with extended saturation threshold through co-doping Nd3+ in CaZnOS: Bi3+, Li+

Much attention has been paid to exploiting phosphors with novel mechanoluminescence (ML); however, there are few reports on how to improve the contrast during imaging and the practical applicability. In this work, CaZnOS:Nd3+,Bi3+,Li+, which generates visible and near-infrared light emission under both external stress and ultraviolet excitation, has been prepared and investigated. Effective energy transfer from the Bi3+ ions to the Nd3+ ions is observed, and this is demonstrated to involve quadrupole-quadrupole interactions. The lifetime of the afterglow from Bi3+ is reduced drastically from 2050 to 122 s, and the saturation threshold is raised greatly from 620 to 3000 N compared with an Nd3+-free sample. Benefiting from less interference from afterglow, the signal-to-noise ratio in ML images increases five-fold. In addition, the five-fold increase in the saturation threshold can be attributed to alterations to some deep trap states, which can lower the utilization of carriers related to ML, upon the incorporation of Nd3+. Moreover, a smart ML pencil has been fabricated. With this smart ML pencil, visible ML from Bi3+ can be used to achieve anti-counterfeiting handwriting with high contrast, and the near-infrared ML from Nd3+ can be used for bio-stress imaging. This visible and near-infrared dual-mode ML phosphor is promising for self-powered stress monitoring and imaging.