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 Cs 2 AgBiBr 6 thin films synthesized via physical vapor deposition emit strong near-infrared luminescence centered at ∼1.24 eV via the Yb 3+ 2 F 5/2 → 2 F 7/2 electronic transition. Robust, reproducible, and stable photoluminescence quantum yields (PLQY) as high as 82.5% are achieved with Cs 2 AgBiBr 6 films doped with 8% Yb. This high PLQY indicates facile and efficient energy transfer from the perovskite host, Cs 2 AgBiBr 6 , to Yb, making Cs 2 AgBiBr 6 the most promising lead-free down-conversion material. Yb 3+ ions substitute into Cs 2 AgBiBr 6 , specifically into the AgBr 6 5− and/or BiBr 6 3− octahedra, leading to a lead-free halide perovskite that converts UV and blue photons to near infrared photons with record 82.5% photoluminescence quantum yield.