Magneto-optical Effect of Dark State in 0D Metal Halides through HT/FC Vibrational Coupling.

Dark excitonic states play a pivotal role in controlling the radiative dynamics of low-dimensional luminescent materials. In this work, we investigate dark states of an emerging zero-dimensional (0D) organic-inorganic hybrid metal halide that diverge markedly from traditional inorganic and organic semiconductors. Our studies reveal that when the dark states dominate the emission, the 0D material exhibits an anomalous giant magneto-blueshift of approximately 9 meV at 7 T. Spectroscopic analysis indicates that the magnetic field modulates the dark state decay pathways, thereby inducing a crossover from the first-order Herzberg-Teller (HT) vibrational coupling mode to the zero-order Franck-Condon (FC) emission mechanism. This field-dependent modulation of dark exciton dynamics underscores the strong interplay between electron-phonon coupling and spin-orbit interactions in these 0D hybrid systems. Our findings provide important insights into the fundamental photophysical processes in these unique materials and open avenues for engineering novel optoelectronic devices.