singlet-triplet energy transfer 

https://doi.org/10.1351/goldbook.S05701
Transfer of excitation from an electronically excited donor in a @S05699@ to produce an electronically excited acceptor in a @T06503@.
Source:
PAC, 1996, 68, 2223. (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2273 [Terms] [Paper]