Fig. 4: Fluorescent behavior of P(NIPAm-co-Tpy) hydrogels.

a Images showing the multi-color fluorescent behavior of PIH. The emission color can be easily adjusted to red, green, or yellow upon coordination with Eu³⁺, Tb³⁺, or their mixtures. All fluorescent emissions can be quenched by Fe³⁺. b Fluorescence spectra (λex = 254 nm) of PIH treated with Eu³⁺, Tb³⁺, their mixtures and Fe³⁺. c Illustrations showing the multi-color pattern. d Images showing the patterning process on the surface of PIH by ionoprinting. e Illustrations showing the operation of dual-encryption by integrating pattern fluorescence and thermo-responsive shape-morphing of PIH. Number-shaped filters containing Eu³⁺ and trapezoid-shaped filters containing Fe³⁺ were ionoprinted onto the upper and lower surfaces of PIH, respectively. The hydrogel was then immersed in 50 °C water to trigger thermo-responsive shape-morphing, thereby shielding the fluorescent pattern. f Images showing the information encryption process. Scale bars: 0.5 cm.