Bound pairs of polarons mutually attracted by the lattice distortion in a solid.
See also: self-localized excitations (in conjugated organic polymers)
Source:
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 309 (https://doi.org/10.1351/pac200779030293)