Ubiquitous Near-Band-Edge Defect State in Rare-Earth-Doped Lead-Halide Perovskites

CsPb(Cl1-xBrx)3(0 <= x <= 1) nanocrystals and thinfilms doped with a series oftrivalent rare-earth ions (RE3+=Y3+,La3+,Ce3+,Gd3+,Er3+,Lu3+) have been prepared andstudied using variable-temperature and time-resolved photoluminescence spectroscopies. Wedemonstrate that aliovalent (trivalent) doping of this type universally generates a new and often-emissive defect state ca. 50 meV inside the perovskite band gap, independent of the specificRE3+dopant identity or of the perovskite form (nanocrystals vs thinfilms). Chloride-to-bromideanion exchange is used to demonstrate that this near-band-edge photoluminescence shifts withchanging band-gap energy to remain just below the excitonic luminescence for all compositionsof CsPb(Cl1-xBrx)3(0 <= x <= 1). Computations show that this shift stems from the effect of the changing lattice dielectric constantson a shallow defect-bound exciton. Microscopic descriptions of this dopant-induced near-band-edge state and its relation toquantum cutting in Yb3+-doped CsPb(Cl1-xBrx)3are discussed.