Interface Defect and Spatial Charge Transfer Contribute to the Dynamic Anticounterfeiting and Fingerprint Recognition...

The Ba_1-xCa_xMoO₄ and BaMo_1-xW_xO₄ (x = 0.5-0.9) phosphors were synthesized by the polyacrylamide gel method. The introduction of Ca ion into BaMoO₄ formed a type I heterojunction between BaMoO₄ and CaMoO₄, while W ion was added to BaMoO₄ formed a single phase of BaMo_1-xW_xO₄. The interaction between interfaces and defects causes a reduction in the band gap (E_g) value of the Ba_1-xCa_xMoO₄ phosphor and an increase in the E_g value of the BaMo_1-xW_xO₄ phosphor due to the Burstein-Moss effect compared to BaMoO₄. The orange-red fluorescence peaks at 638 and 680 nm were detected in Ba_1-xCa_xMoO₄ due to the formation of a type I band arrangement heterojunction, as well as the defects at the interface, as a result of a 530-nm excitation wavelength. The difference is that when excited by a wavelength of 256 nm, the BaMo_1-xW_xO₄ phosphor emits purple and blue light emission peaks at 378 and 424 nm, respectively. The ¹T₂ → ¹A₁ transition in [MoO₄]^2- and [WO₄]^2- leads to the blue-violet luminescence of the BaMo_1-xW_xO₄ phosphor. These phosphors have been found to be suitable for dynamic anticounterfeiting and fingerprint recognition applications due to their special interface defect and spatial charge transfer.