Excitation-dependent multi-color emission in lead-free double perovskites with Er3+–Yb3+ cross relaxation for information encryption

Lead-free halide double perovskites have emerged as ideal host materials for ion doping due to their inherent structural stability, low toxicity, and unique ability to accommodate multiple luminescent centers. These characteristics render them highly promising candidates for advanced applications such as intelligent optical anti-counterfeiting and information encryption. In this work, we present a multimodal excitation luminescence design of co-doped Cs2NaScCl6:Er3+, Yb3+, and Sb3+ phosphors. The incorporation of Er3+ and Yb3+ ions not only enables both downconversion and upconversion luminescence with different excitations but also endows multi-color emissions from green to red light through the unique cross-relaxation effect. Furthermore, the introduction of Sb3+ ions creates an efficient energy transfer pathway from self-trapped excitons to Er3+ ions and also achieves a synergistic enhancement of the photoluminescence quantum yield, reaching an outstanding value of 71.24%. Leveraging these excitation-dependent multi-color luminescent properties, we implement multilevel anti-counterfeiting and information encryption applications. This work highlights the significant advantages of ion-doped rare-earth-based double perovskites in advanced optical security technologies.