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 similar to 1.24 eV via the Yb3+ 2F5/2 -> F-2(7/2) 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.