Multicolor-emitting Er3+ and Er3+/Yb3+ doped Zn2GeO4 phosphors combining static and dynamic identifications for advanced anti-counterfeiting application

Abstract

Anti-counterfeiting labels based on luminescence materials are a newly emerging technique for protecting legal goods and intellectual property. In the anti-counterfeiting field to prevent forgery and cloning, luminescence materials with properties different from the commercialized and traditional ones are in urgent need. In this work, multicolor-emitting Er³⁺ single-doped and Er³⁺/Yb³⁺ co-doped Zn₂GeO₄ phosphors combining static and dynamic identifications were developed in order to achieve advanced anti-counterfeiting application. The variation of trap content with increasing the doping content of rare earth ions was analyzed through X - ray photoelectron spectroscopy, thermoluminescence analysis. It was found that there are two types of traps with different depth in Zn₂GeO₄ phosphors. The depths of the traps were experimentally confirmed to be 0.68 and 0.79 eV, respectively. The transient photocurrent response measurement confirmed the existence of charge carriers, and the mechanism for long persistent luminescence was deduced. The multicolor upconversion mechanisms under 980 and 1550 nm excitation were also discovered. Based on the multicolor steady and transient emission features, an anti-counterfeiting pattern was designed using the phosphors. Static and dynamic identification was demonstrated and presented in detail. Finally, it is indicated that the studied phosphors are excellent candidates for potential applications in luminescence anti-counterfeiting labels.

Keywords: Anti-counterfeiting; Long persistent luminescence; Phosphor; Photocurrent; Zn(2)GeO(4).