Multicolor luminescence and anti-counterfeiting applications in Cs2KGdCl6 double perovskite

Abstract

Recently, the rich energy level structure of Ln³⁺ ions has introduced new diversity into the double perovskite material, making it a research hotspot. The Sb³⁺/Ho³⁺ co-doped Cs₂KGdCl₆ double perovskite was synthesized using a simple dissolve–dry method in this study, which exhibits not only a broadband green emission from self-trapped excitons (STEs) but also a characteristic red emission from the f–f transitions of Ho³⁺. Experimental results confirmed effective energy transfer channels between STEs and Ho³⁺, with Sb³⁺ sensitization significantly enhancing the Ho³⁺ emission intensity. Further introduction of Yb³⁺ achieves dual-mode multicolor emission including down-shifting (DS) and up-conversion (UC). Under 315 nm and 450 nm excitation, the obtained material displays blue green and red emissions, respectively. Under 980 nm near-infrared excitation, the emission color changes from pale yellow to orange red with increasing laser power. A compound fluorescent anti-counterfeiting label was fabricated based on 1%Sb³⁺/13%Ho³⁺/35% Yb³⁺ co-doped Cs₂KGdCl₆. Finally, Tm³⁺ doping enabled efficient UC white light emission. This work provides new insights for achieving white-light emission and anti-counterfeiting applications via metal ion doping in lead-free double perovskites.