Multi-mode photoluminescence inks based on lanthanide-doped multilevel core-shell microspheres for advanced anti-counterfeiting applications

Abstract

Development of advanced luminescent nanomaterials and technologies is of great significance for anticounterfeiting applications in global economy, security, and human health. In this work, we have designed two types of anti-counterfeit materials. (1) The dual excitation mode core–shell microsphere is based on SiO2 core, with the GdVO4:Yb,Er upconversion luminescent inner layer, SiO2 shell separator, and Gd2O3:Eu@SiO2 downconversion luminescent layer are sequentially deposited on it via co-precipitation method. The microspheres have a five-layer core–shell structure with an overall diameter of ∼ 146 nm and enables the spatial separation of Er3+ and Eu3+, which prevents the cross-relaxation of Er3+. The microspheres were prepared into an upconversion/downconversion excitation mode luminescent ink, with inkjet-printed patterns that only extract information when excited by 254 nm and 980 nm excitation. (2) The core–shell-shell SiO2@AIPA-S-Si-Tb@SiO2 microspheres have been synthesized by using organic ligands ((HOOC)2C6H3NHCONH(CH2)3Si(OCH2CH3)3) (defined as AIPA-S-Si) connected with Tb3+ ions and silica through covalent bond. The microspheres have a sandwich structure with an overall diameter of ∼ 100 nm and show bright green light. The sandwich structure and five-layer core–shell structure was mixed proportionally to obtain orange-red, white, and yellow emission ink under 254 nm, green emission under 310 nm, and green emission under 980 nm excitation.