Manipulation of Upconversion Luminescence in Heavily Lanthanide‐Doped Halide Double Perovskites for Optical Information Storage

Upconversion (UC) process involves diverse energy levels and photoluminescence modes, however, it faces the challenge of concentration quenching of the doped lanthanide ions with multiple luminescence centers. Herein, Yb 3+ /Ho 3+ and Yb 3+ /Tm 3+ are heavily codoped into the lead‐free halide double perovskite single crystal Cs 2 NaErCl 6 , enabling the controlled energy transfer UC process, and accordingly, the UC materials exhibit anti‐concentration‐quenching owing to the defect tolerance characters. Depending on different doping couples, the UC materials show green and red emissions under the 980 nm laser excitations. Moreover, the green‐to‐red emission ratio in Yb 3+ /Tm 3+ codoped Cs 2 NaErCl 6 changes dynamically with the increasing pumping intensity due to the different sensitivities of the excited energy levels. This study provides a renewed direction of the lanthanide ions heavily‐doped halide double perovskites toward UC materials and facilitates the development of new smart luminescence materials for optical information storage applications.