Defect-assisted dynamic multicolor modulation in KLu 3 F 10 :Tb crystals for anti-counterfeiting.

Excitation-dependent dynamic multicolor luminescent materials show potential for promising applications in the field of anti-counterfeiting. However, for most ultraviolet (UV)-excited lanthanide-doped materials, more than two types of activators are incorporated to realize multicolors. In this study, for the first time, KLu 3 F 10 :Tb crystals were used to realize excitation-dependent multicolor emissions. The morphology was modified by tuning the surface-coated citric acid (CA) content. During hydrothermal reactions, fluorine vacancy defects are formed on the crystal surface, and carboxyl groups (-COOH) are coated on the crystal surface to maintain the charge balance. Under 254 nm UV excitation, typical Tb 3+ green emissions were observed, while a strong broadband emission peaking at 442 nm appeared in addition to these Tb 3+ emissions under 365 nm excitation. The energy transfer (ET) process between the defect state and Tb 3+ is clarified. This work may promote the development of single-type activator-doped multicolor luminescent materials for high-level anti-counterfeiting.