Bright Triplet Self-Trapped Excitons to Dopant Energy\nTransfer in Halide Double-Perovskite Nanocrystals

Abstract

For\ninorganic semiconductor nanostructure, excitons in the triplet\nstates are known as the “dark exciton” with poor emitting\nproperties, because of the spin-forbidden transition. Herein, we report\na design principle to boost triplet excitons photoluminescence (PL)\nin all-inorganic lead-free double-perovskite nanocrystals (NCs). Our\nexperimental data reveal that singlet self-trapped excitons (STEs)\nexperience fast intersystem crossing (80 ps) to triplet states. These\ntriplet STEs give bright green color emission with unity PL quantum\nyield (PLQY). Furthermore, efficient energy transfer from triplet\nSTEs to dopants (Mn²⁺) can be achieved, which leads to\nwhite-light emitting with 87% PLQY in both colloidal and solid thin\nfilm NCs. These findings illustrate a fundamental principle to design\nefficient white-light emitting inorganic phosphors, propelling the\ndevelopment of illumination-related applications.