High photoluminescence quantum yield near-infrared emission from a lead-free ytterbium-doped double perovskite

When excited by photons with energies greater than 2.2 eV, the bandgap energy, Yb-doped Cs₂AgBiBr₆ thin films synthesized via physical vapor deposition emit strong near-infrared luminescence centered at ∼1.24 eV via the Yb³⁺ ²F5/2 → ²F7/2 electronic transition. Robust, reproducible, and stable photoluminescence quantum yields (PLQY) as high as 82.5% are achieved with Cs₂AgBiBr₆ films doped with 8% Yb. This high PLQY indicates facile and efficient energy transfer from the perovskite host, Cs₂AgBiBr₆, to Yb, making Cs₂AgBiBr₆ the most promising lead-free down-conversion material.