Tailoring trap distribution via metal cation substitution in SrxBa1-xSi2O2N2 lattices for multicolor and multimodal dynamic information encryption strategy

Abstract

Traditional anti-counterfeiting technology based on fluorescent materials is usually single-color emission and far from enough to meet the growing demand for anti-counterfeiting with high-level security. Here, dual luminescent centers with blue emission at 470 nm and green-yellow emission at 546 nm have been successfully achieved by controlling the Eu2+ sites in the SrxBa1-xSi2O2N2 (x = 0.25–0.50) host lattices via fine-tuning of Sr contents (x). Notably, Sr0.50Ba0.50Si2O2N2: 0.02Eu2+ exhibits particular optical information storage properties with intense yellow emission and can repeat the corresponding image patterns under the thermal stimulus, which can be regarded as an essential candidate in multicolor anti-counterfeiting technology. Further, the different luminescent center-trap center pairings have been found in Sr0.33Ba0.67Si2O2N2: 0.02Eu2+ due to the substitution of Ba2+ and Sr2+ by Eu2+ to generate blue and yellow luminescent centers and the substitution of N3− for O2− in the Sr and Ba lattices resulting in oxygen vacancies. Typically, Sr0.33Ba0.67Si2O2N2: 0.02Eu2+ exhibits a cool white emission in photoluminescence (PL) mode and changes to yellow emission in persistent luminescence (PersL) mode. Moreover, Sr0.33Ba0.67Si2O2N2: 0.02Eu2+ displays a thermochromic phenomenon (from cool white emission to blue emission) in thermally stimulated luminescence (TSL) mode, attributed to the different trap depths in Sr and Ba lattice. Hence, flexible film for optical information storage and patterns for multimodal dynamic anti-counterfeiting are fabricated using Sr0.33Ba0.67Si2O2N2: 0.02Eu2+. Finally, a dynamic optical information encryption and decryption strategy for Morse code is developed based on the different properties of SrxBa1-xSi2O2N2: 0.02Eu2+ (x = 0.25, 0.30, 0.33, and 0.50). The results demonstrate that SrxBa1-xSi2O2N2: 0.02Eu2+ (x = 0.25–0.50) phosphors can be potential candidates in optical information storage and optical anti-counterfeiting applications.