Trap engineering in ZnGa2O4:Tb3+ through Bi3+ doping for multi-modal luminescence and advanced anti-counterfeiting strategy

Optical information encryption based on luminescence materials have received much attention recently. However, the single luminescence mode of the luminescence materials greatly limits its anti-counterfeiting application with high safety level. Here, a series of luminescence materials of Tb 3+ and Bi 3+ co-doped ZnGa 2 O 4 phosphors with great correspondence in photoluminescence (PL), persistent luminescence (PersL), and thermoluminescence (TL) modes was synthesized by the conventional solid-phase method for the application in multi-modal anti-counterfeiting fields. Under the excitation of 254 nm, ZnGa 1.99 O 4 :0.01 Tb 3+ , yBi 3+ (y = 0.001,0.002) sample exhibited a broad blue emission band (the transition from [GaO 6 ]) at 440 nm and the characteristic emission peaks of Tb 3+ at 495 nm, 550 nm, 591 nm and 625 nm, corresponding to the transitions of 5 D 4 - 7 F n (n = 6, 5, 4, 3), respectively. Interestingly, the co-doping of Bi 3+ ions improve the crystallinity and particle size of the phosphor, subsequently enhanced the PL intensity of Tb 3+ to 6 times that of Tb 3+ singly doped ZnGa 2 O 4 phosphor. Further, the flexible films with multi-modal luminescence properties have been fabricated through the unique TL and PersL characteristics of ZnGa 2 O 4 : Tb 3+ , Bi 3+ phosphors, including “Optical information storage film”, “snowflake and characters” and “QR code”. Moreover, a set of optical information encryption is obtained by combining ZnGa 2 O 4 :Tb 3+ , Bi 3+ phosphor and red emitting phosphor. The results indicate that ZnGa 2 O 4 :Tb 3+ , Bi 3+ phosphor with multi-modal stimulus response can be expected to be potentially used in the applications of optical information storage and anti-counterfeiting fields.