Band-gap engineering enabled emission switch in solid-solution phosphors LiIn1-xScxGeO4:Bi3+ for spectral-temporal anti-counterfeiting

Abstract

The interaction between matrix lattice and doped activator has long been pivotal topic in the research of the state-of-the-art functional materials, particularly luminescent materials. With the ceaseless development of advanced anti-counterfeiting, there are imperative need for developing luminescent materials with wide emission tunability, excellent visibility, and adjustable persistent luminescence. Herein, we present a paradigm to obtain great emission tunability in a solid-solution phosphors LiIn1-xScxGeO4:Bi3+ (x = 0–1) via band-gap engineering. With the increase in Sc content, the band-gap enlarges, causing the Bi3+ emissions gradually shift from 580 to 456 nm. As Sc substitution continues, the Bi3+ emissions transfer from the metal-to-metal charge transfer band to the inter s-p transition, resulting in a rapid shift in emission from 456 to 356 nm. This emission shift not only achieves a record total tunability of 224 nm among Bi3+-doped solid-solution phosphors but also an informative band-gap dependent emission mechanism of the Bi3+ activator. Furthermore, the samples gradually exhibited a persistent luminescence through the substitution process, attributed to the increasing traps by the thermoluminescence analysis. Leveraging these unique spectral properties, we designed two types of patterns that can be distinguished from color and time within the visible light range, demonstrating that the obtained phosphors can serve as promising candidate materials for spectral-temporal anti-counterfeiting.