Evolution of a Snowflake-Like Mn ²⁺ Doped Cs ₂NaBiCl ₆ Nanosheet Phosphor Driven By Cation Exchange

Effectively transforming the dimension of lead-free metal halide perovskite is important for many applications, but this remains difficult to achieve synthetically. Here, we first report an unusual morphology evolution from micro-sized 3D octahedron to 2D snowflake-like nanosheet in the Mn2+ doping process of Cs2NaBiCl6 by a post-synthesized cation exchange strategy, which can obviously enhance the photoluminescence quantum efficiency (PLQY) of Cs2NaBiCl6:Mn2+ phosphor due to the surface passivation effect of this morphologic evolution. This surprising evolution is ascribed to morphology collapse and reconstruction induced by Mn2+ exchange. The obtained phosphor exhibits enhanced 31.56% PLQY, which is two-fold higher than that synthesized by traditional co-precipitation way, broad emission spectrum and good PL color stability under 150℃. Combining with Cs2SnCl6:1mol%Bi3+ phosphor to fabricate phosphor-converted light-emitting diode, showing a bright white light emission with Ra=88, CCT=4320 K and CIE (0.36, 0.33) and a good application potential in high-resolution PL imaging agents. This work proves the feasibility of the post-synthetic cation exchange method for impurity doping in micron-scale lead-free metal halide perovskite and provides a new idea for independent study of doping behavior.