| Pure AgI particles experience a color evolution at theβto a phase transition temperature. However, the photoinstability of AgI due to its labile photodecomposition to metallic Ag under light illumination greatly hinders its diverse applications. Herein, it was found for the first time that the formation of AgI/TiO2 nanocomposite not only result in a considerable reduction of thermochromic transition temperature of AgI as well as excellent thermochromic reversibility, but also leads to excellent photostability under the illumination of indoor fluorescent lamp.AgI/TiO2(P25), AgI/Rutile-TiO2 and AgI/Anatase-TiO2 nanocomposite was prepared and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and diffusive reflectance UV-vis (DRUV-vis) absorption spectra at different temperatures. All the three AgI/TiO2 samples exhibit thermochromic switching phenomena at the phaseβ-αtransition temperature of AgI with the evolution of its color from light yellow at ambient temperature to dark khaki at 150℃. Besides, the AgI/TiO2(P25) nanocomposite exhibits a hysteresis loop on the heating/cooling cycle, which is attributed to the suppression of a toβphase transition due to the higher surface energy of AgI nano particles.Based on the characterization results by photoluminescence, transient photocurrent decay and positron annihilation spectra, it is concluded that large size surface defects, such as I- vacancy clusters (e.g. Ag+I-v-Ag+-I-v-Ag+) on the surface of AgI as deep electron traps, are responsible to photodecomposition of pure AgI. The excellent photostability for the AgI/TiO2 nanocomposite is due to the following reason:the surface I- vacancy clusters as deep electron traps in pure AgI are replaced by Ag+-O2--Ti4+ bonds on the interface of AgI/TiO2, thus Agn cluster formation through the surface migration of photogenerated Ag atoms is completely inhibited, resulting in the inhibition of photodecomposition of AgI.
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