Luminescence regulation of Sb<sup>3+</sup> in 0D hybrid metal halides by hydrogen bond network for optical anti-counterfeiting

The Sb³⁺ doping strategy has been proven to be an effective way to regulate the band gap and improve the photophysical properties of organic-inorganic hybrid metal halides (OIHMHs). However, the emission of Sb³⁺ ions in OIHMHs is primarily confined to the low energy region, resulting in yellow or red emissions. To date, there are few reports about green emission of Sb³⁺-doped OIHMHs. Here, we present a novel approach for regulating the luminescence of Sb³⁺ ions in 0D C₁₀H₂₂N₆InCl₇·H₂O via hydrogen bond network, in which water molecules act as agents for hydrogen bonding. Sb³⁺-doped C₁₀H₂₂N₆InCl₇·H₂O shows a broadband green emission peaking at 540 nm and a high photoluminescence quantum yield (PLQY) of 80%. It is found that the intense green emission stems from the radiative recombination of the self-trapped excitons (STEs). Upon removal of water molecules with heat, C₁₀H₂₂N₆In_1-xSb_xCl₇ generates yellow emission, attributed to the breaking of the hydrogen bond network and large structural distortions of excited state. Once water molecules are adsorbed by C₁₀H₂₂N₆In_1-xSb_xCl₇, it can subsequently emit green light. This water-induced reversible emission switching is successfully used for optical security and information encryption. Our findings expand the understanding of how the local coordination structure influences the photophysical mechanism in Sb³⁺-doped metal halides and provide a novel method to control the STEs emission.