Magnetic hyperfine modulation of dye-sensitized delayed fluorescence in organic crystals

Abstract

Magnetic fields on a hyperfine scale can modulate dye-sensitized delayed fluorescence from organic crystals at room temperature. This hyperfine modulation (HFM) has been found to depend on the orientation of the field in the $\mathrm{ac}$ plane of rhodamine-$B$-sensitized anthracene. The anisotropy can be explained by an electron-hole spin-spin interaction in the dye-anthracene charge-transfer state formed following photoexcitation of the sensitizing dye on the crystal surface. Increased dye concentration broadens the field-dependence curve, presumably as a result of dye-aggregation effects. HFM has also been found in other dye-crystal systems.