Implanting bismuth in color-tunable emitting microspheres of (Y, Tb, Eu)BO3 to generate excitation-dependent and greatly enhanced luminescence for anti-counterfeiting applications

To prevent counterfeiting, a lot of advanced security technologies have been developed, including luminescent printing. Therefore, the pigments with advanced security features are urgently pursued for luminescence printing-based anti-counterfeiting technology. Here, micron-sized spheres of hexagonal-structured and color-tunable emitting (Y, Tb, Eu, Bi)BO 3 have been rapidly synthesized by microwave processing, followed by a proper annealing. Incorporation of Bi 3+ greatly enhances the emission intensity of Eu 3+ and of Tb 3+ . Under the excitation at 260 nm, the spheres exhibit UV emission at 330 nm ( 3 P 1 → 1 S 0 transition of Bi 3+ ), green emission at 546 nm ( 5 D 4 → 7 F 5 transition of Tb 3+ ) and orange-red emission at 592 nm ( 5 D 0 → 7 F 1 transition of Eu 3+ ), mainly due to the three energy transfer processes of Bi 3+ →Tb 3+ , Bi 3+ →Eu 3+ , and Tb 3+ →Eu 3+ . However, under the excitation at 230 nm, the Tb 3+ →Eu 3+ energy transfer contributes to the orange-red emission of Eu 3+ and the green emission of Tb 3+ , in the absence of Bi 3+ emission. The maximum energy transfer efficiency of Bi 3+ → "Eu 3+ and Tb 3+ " and Tb 3+ → Eu 3+ is 63% and 50% for (Y 0.883 Tb 0.02 Eu 0.09 Bi 0.007 )BO 3 . The (Y 0.963 Tb 0.02 Eu 0.01 Bi 0.007 )BO 3 spheres exhibit a distinct excitation-dependent luminescence behavior. Facile switching the excitation wavelength from 260 nm to 230 nm yields emission color changing from orange to green yellow, which possesses the advanced security feature.