Engineering Eu3+-activated molybdenum tellurates via alkali metal co-doping for enhanced luminescence in advanced lighting and security ink applications

Abstract

Eu³⁺-activated red-emitting phosphors are of sustained interest for multifunctional applications. However, their poor stability under harsh conditions, such as high temperatures and aqueous environments, critically limits their advancement in lighting and optical security technologies. Herein, the molybdenum tellurate Ca₃(TeO₃)₂(MoO₄) (CTMO) is activated by Eu³⁺ for the first time, realizing bright red emission with high stability. In parallel, to reduce defect-induced non-radiative transitions due to the non-equivalent substitution of Eu³⁺ for Ca²⁺, the enhancement of co-doping alkali metal (A⁺ = Li⁺, Na⁺, K⁺) on the red luminescence is demonstrated thoroughly. The incorporation of the co-dopant Na⁺ delivers a 3-fold enhancement in emission intensity, along with a 1.56-fold increase in quantum efficiency. Besides, the optimized CTMO:Eu³⁺,Na⁺ powder exhibits improved luminescence stability at high temperature. When incorporated into a white-lighting device, warm white light with low correlated color temperature (CCT = 3775 K) is achieved. Meanwhile, the security ink is prepared by dispersing the resulting powder into polydimethylsiloxane (PDMS) matrix, enabling screen printing, coating, and handwriting to create security patterns on various substrates (woven/non-woven fabrics, paper, glass, and plastic sheets). The ink retains bright luminescence after immersion in water for 40 days. This investigation significantly boosts the multifunctional applicability of Eu³⁺-activated red-emitting phosphors for lighting and long-lasting optical security.