Transfer of excitation from an electronically excited donor in a singlet state to produce an electronically excited acceptor in a triplet state.
See: energy transfer (in photochemistry), spin conservation rule
Source:
PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2273 (https://doi.org/10.1351/pac199668122223)