Unlocking ultra-stable blue emission from Ytterbium- and erbium-doped metal halides

Abstract 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.