Construction of energy transfer channels from [SbCl6]3− to Ln3+ (Ln3+ = Ho3+, Er3+) in Cs2NaGdCl6 for advanced anti-counterfeiting materials

The existence of energy transfer channels from the self-trapped exciton (STE) emission to lanthanide (Ln3+) ions in double perovskites (DPs) opens up new possibilities for high security anti-counterfeiting applications. In the present investigation, we synthesized Sb3+/Ho3+/Er3+ doped Cs2NaGdCl6 rare-earth-based DPs using a simple solvothermal method, whose luminescence could be quenched by water and restored after drying. The efficient down-shifting (DS) red emission from the 4f–4f transition of Ho3+ was enhanced 8-fold due to the energy transfer of STEs → Ho3+ ions via Sb3+ sensitization. The DS and up-conversion (UC) dual-mode multicolor emissions were obtained by further introducing Er3+. Specifically, the DS luminescence of the tri-doped sample under the UV region and that under 448 nm irradiation were white and red, respectively; and the UC luminescence under 980 nm irradiation was green. In view of their stimulus response to water and dual-mode multicolor luminescence properties, advanced anti-counterfeiting materials based on the obtained samples were designed.