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)BO3 have been rapidly synthesized by microwave processing, followed by a proper annealing. Incorporation of Bi3+ greatly enhances the emission intensity of Eu3+ and of Tb3+. Under the excitation at 260 nm, the spheres exhibit UV emission at 330 nm (3P1→1S0 transition of Bi3+), green emission at 546 nm (5D4→7F5 transition of Tb3+) and orange-red emission at 592 nm (5D0→7F1 transition of Eu3+), mainly due to the three energy transfer processes of Bi3+→Tb3+, Bi3+→Eu3+, and Tb3+→Eu3+. However, under the excitation at 230 nm, the Tb3+→Eu3+ energy transfer contributes to the orange-red emission of Eu3+ and the green emission of Tb3+, in the absence of Bi3+ emission. The maximum energy transfer efficiency of Bi3+→ “Eu3+ and Tb3+” and Tb3+→ Eu3+ is 63% and 50% for (Y0.883Tb0.02Eu0.09Bi0.007)BO3. The (Y0.963Tb0.02Eu0.01Bi0.007)BO3 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.