An effect accompanying concentration quenching in some cases, namely the formation of a new bimolecular species which is capable of emission (excimer- and exciplex-luminescence).
Source:
PAC, 1984, 56, 231. 'Nomenclature, symbols, units and their usage in spectrochemical analysis-Part VI: molecular luminescence spectroscopy' on page 235 (https://doi.org/10.1351/pac198456020231)