Energy transfer from self-trapped excitons to rare earth ions in Cs2ZrCl6 perovskite variants

Rare earth ion doping in metal halides has been a promising method for imparting and tailoring their optical and optoelectronic performances towards versatile optical applications. In this work, the relationships among intrinsic self-trapped excitons (STEs), sub-band gap defects and rare earth ions Tb3+ in Cs2ZrCl6:Tb3+ perovskite variants were established. Cs2ZrCl6 exhibits dual emission, deriving from the intrinsic STEs and sub-band gap defects owing to the Zr4+ or Cl- vacancies, respectively. Doping Tb3+ facilitated the characteristic emission (D-5(4)-F-7(J=6,5,4,3)) of Tb3+ ions and the energy transfer from STEs to Tb3+ ions. Moreover, the participation of defect states and thermally activated delayed fluorescence (TADF) might lead to a high concentration of STEs, which in turn causes the abnormal thermal quenching effect. These findings not only provide a more in-depth understanding of the luminescence properties of Cs2ZrCl6, but also provide a new direction towards achieving tunable emission colors based on the energy transfer from STEs to rare earth ions.