High-security anti-counterfeiting through upconversion luminescence

Upconversion luminescence is characterized by the conversion of near-infrared excitation into ultraviolet and visible emissions through a special class of doped optical materials. Recent advances in chemical synthesis have enabled the precise incorporation of multiple dopant ions into a single substrate of well-controlled size and morphology, which render emissions with distinguishable spectroscopic fingerprints as well as spatially and temporally resolved features. These luminescence characteristics hold great promise in anti-counterfeiting applications by encoding high-capacity optical codes. In this review, we focus on recent advances in anti-counterfeiting technology that exploits the remarkable tunability of upconversion luminescence to design optical codes with high-level security. We discuss various approaches for the design of upconversion materials and construction of upconversion codes, along with an analysis of future challenges for upconversion-based anti-counterfeiting. (C) 2021 Elsevier Ltd. All rights reserved.