<p>Rare earth-doped luminescent materials typically produce characteristic fluorescence emissions associated with the rare earth elements. Here, we report remarkable non-characteristic blue emissions from ytterbium (Yb³⁺)- and erbium (Er³⁺)-doped organic-inorganic metal halides, (BDPA)₂MCl₄ (BDPA⁺ = benzyldimethylphenylammonium; M²⁺ = Cd²⁺, Zn²⁺). Both Yb³⁺ and Er³⁺ ions are commonly used as dopants in phosphors, which generally lead to near-infrared emissions. Theoretical calculations suggest the unique blue emission arises from Yb³⁺/Er³⁺-induced exciton radiative recombination from BDPA⁺ to Cl⁻, which suppresses the characteristic emissions of these rare earth ions. More notably, owing to structural stability of (BDPA)₂MCl₄, the Yb³⁺/Er³⁺-activated phosphors demonstrate high water resistance, maintaining both stability and photoluminescence (PL) in water for over two months. Further, when these crystals are dissolved in N,N-dimethylformamide or dimethyl sulfoxide, the resulting solution continues to exhibit PL with a high quantum yield of ~90%, making it suitable for use as liquid-phase X-ray scintillators.</p><p></p>