Low-dimensional lead-free metal halides have recently attracted a great deal of attention for their unique photoluminescence properties. In this work, a new all-inorganic zero-dimensional (0D) rare-earth perovskite, namely Cs₂ScCl₅·H₂O is reported. The 0D crystal exhibits a rare phenomenon of excitation-wavelength dependent emission from blue-green to white to yellow at room temperature. Spectroscopic characterizations indicate the tunable emission is originated from two distinct self-trapped exciton states. In addition, the yellow emission quantum yield can be enhanced from 1.2% to ≈100% by doping Sb³⁺ ions into the crystal. The work not only presents a new all-inorganic semiconductor with tunable emission colors, but also provides a design strategy for developing nontoxic and high-performance light-emitting materials.