The zero-dimensional (0D) (H5O2)(C4H14N2S2)2BiCl8: Sb3+ single crystal is obtained by the cooling crystallization method. Surprisingly, this compound shows reversible photoluminescence (PL) upon H5O2+Cl- removal and insertion. To be specific, the release of H5O2+Cl- resulted in red-orange emission with a very low photoluminescence quantum yield (PLQY). While on the reuptake of it, a bright yellow emission with a nearly 10-fold increase of PLQY was observed. Density functional theory (DFT) calculations and temperature-dependent PL experiments reveal that significant [SbCl6]3- octahedron distortion induced by guest (H5O2+Cl-) removal at the ground state, especially at the excited state, is responsible for the disparate PL performance. Encouragingly, we also found that (C4H14N2S2)2BiCl7: Sb3+ exhibits a fast response (<3 s) to dilute hydrochloric acid with naked-eye perceivable PL color changes, rendering it a potential sensing material for hydrochloric acid.