Polyurethane-coated double perovskite (Cs4Mn1-xCdxBi2Cl12) significantly improves stability and flexible anticounterfeiting

Impurity doping is widely recognized as an effective approach to enhancing the photophysical properties and expanding the application potential of halide perovskites. In this study, we employed a room-temperature co-precipitation method to synthesize luminescent powders of Cs3Bi2Cl9 perovskite doped with varying concentrations of Mn2+. As Mn2+ content increased, a phase transition from Cs3Bi2Cl9 to Cs4MnBi2Cl12 occurred, along with a continuous increase in luminescent intensity. Introducing Cd2+ ions mitigated the Mn2+-Mn2+ coupling effects, significantly enhancing luminescent intensity. Additionally, we investigated the structural and luminescent behavior of Cs4Mn1-xCdxBi2Cl12 in humid environments, revealing that water induces crystal dissociation and phase transitions, leading to fluorescence quenching. To address the common issue of limited stability in halide perovskites, we have innovatively chosen thermoplastic polyurethane (TPU) as the organic encapsulation material. This strategy effectively inhibits environmentally induced phase transitions, preserving the high brightness of Cs4Mn1-xCdxBi2Cl12 phosphors while significantly enhancing their thermal and water stability. Additionally, TPU imparts excellent flexibility and transparency to the phosphors, offering promising potential for applications in flexible anti-counterfeiting technologies. •Phase transition and luminescence mechanisms are studied across varying doping concentrations.•Water molecules cause dissociation and phase transition in the (Cs4Mn1-xCdxBi2Cl12) crystal structure.•TPU coating prevents phase transitions, enhances stability, and enables flexible fluorescence emission.•Offers guidance on fluorescence enhancement for lead-free perovskites and practical perovskite applications.