Reversible photochromic and photoluminescence in iodide perovskites

Color imaging experiment demonstrates a photochromic behavior of mixed-halide perovskites upon dark and light excitation, while the color emitted by the crystals changes from red to yellow and vice versa with the intensity of excitation light source. Unlike the photochromic property commonly observed in solution-state polymer materials, solid-state perovskite materials with photochromic behavior might open wide applications in consumer products and electronic devices. In the next part, we report on a reversible photoluminescence (PL) peak in iodide-based organic-inorganic lead halide perovskite materials under a 2-photon absorption process, while tuning the excitation wavelength. Intriguingly, two shorter wavelength peaks are visible and become prominent when the excitation photon energy is being tuned in the high energy spectrum, while laser power is remained constant. The same phenomenon of reversible PL peak is also observed in various iodine-based organic-inorganic halides as well as all-inorganic perovskite single crystals and polycrystals. We attribute to the reversible PL peak phenomenon to the photoinduced structural deformation and the associated change in the optical bandgap of iodide perovskites under the femtosecond laser excitation. Our findings will introduce a degree of freedom in future research as well as adding functionalities to optoelectronic applications in these emerging perovskite materials-based devices.