Multimode Dynamic Photoluminescence of Bi 3+ -Activated ZnGa 2 O 4 for Optical Information Encryption.

Optical storage technology for information encryption is a popular means of safeguarding information. Herein, a Bi 3+ -activated ZnGa 2 O 4 multimode dynamic photoluminescence (PL) material is developed. Upon being irradiated with an ultraviolet lamp at a fixed excitation wavelength of 254 nm, the ZnGa 2 O 4 : x % Bi 3+ ( x = 0.5-5.0) samples exhibit varying degrees of dynamic PL emission due to a distinct Bi 3+ doping effect. The mechanism underlying the dynamic PL of ZnGa 2 O 4 : Bi 3+ associated with Bi 3+ -activated trap concentration modulation is investigated using thermoluminescence spectra. Additionally, the ZnGa 2 O 4 : 5% Bi 3+ sample shows a reversible thermally responsive dynamic PL with a color variation from blue to red upon heating from 283 to 393 K. Predesigned procedures based on single-wavelength-mediated photochromic and thermochromic dynamic PL emissions of ZnGa 2 O 4 : Bi 3+ are designed for rewritable optical data storage and high-level information encryption. Also, an enhanced encryption scheme with a mask encoding technique applying a ZnGa 2 O 4 : Bi 3+ hybridized polyvinylidene difluoride film is then proposed to increase the security level. Accordingly, this work provides a feasible way to rationally design dynamic PL material offering more creative designs for safeguarding information via encryption.