Simultaneously Achieving Multicolor Emission of Down-Shifting and Up-Conversion in Yb3+, Er3+ -Codoped Cs2NaGdCl6 Double Perovskites

Ultraviolet (UV) excited down-shifting (DS) double perovskites with broad emission have potential applications in anti-counterfeiting. However, discovering new materials and achieving multimode luminescence present significant challenges. In this work, a novel double perovskite, Cs2NaGdCl6 is synthesized, with sky-blue self-trapped exciton (STE) emission under UV excitation using a solvothermal method. By incorporating Er3+ ions into Cs2NaGdCl6, green DS and green up-conversion (UC) luminescence are achieved under UV and near-infrared (NIR) excitation. The addition of the sensitizer Yb3+ ion led to a significant enhancement of 21.5-fold in DS red luminescence and 7.5-fold in UC green luminescence. The color of both DS and UC luminescence in Cs2NaGdCl6:Yb3+, Er3+ is further adjusted from green-dominated to red-dominated, due to the cross-relaxation process between Er3+ and Yb3+, Er3+ and Er3+, respectively. The combination of UC and DS luminescence, along with the ability to modulate emission color in rare-earth-based materials, opens new possibilities for high security anti-counterfeiting applications.