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

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 (Yb 3+ )- and erbium (Er 3+ )-doped organic-inorganic metal halides, (BDPA) 2 MCl 4 (BDPA + = benzyldimethylphenylammonium; M 2+ = Cd 2+ , Zn 2+ ). Both Yb 3+ and Er 3+ ions are commonly used as dopants in phosphors, which generally lead to near-infrared emissions. Theoretical calculations suggest the unique blue emission arises from Yb 3+ /Er 3+ -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) 2 MCl 4 , the Yb 3+ /Er 3+ -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.