Fig. 2: Magnetic brightening of the ground dark singlet exciton of single CsPbI3 NCs.
From: The dark exciton ground state promotes photon-pair emission in individual perovskite nanocrystals
a–c Spectra of three different single NCs at 4 K, which present one a, two b, three c exciton recombination ZPLs in zero field. The insets show the corresponding diagrams of exciton fine structure, which are sensitive to shape anisotropy. The levels displayed in red represent the optically active triplet states, while the ground level in gray is the singlet dark state. At 7 T, magnetic splitting and coupling among the fine structure sublevels reveal the entire spectral fingerprint of the bright triplet and the lowest-energy singlet state. d Bright-to-dark relaxation with a one-phonon process is inhibited in lead halide perovskites (left panel). Thermal mixing between dark and bright states occurs via a two-phonon process (right panel).
