Solid-state exciplex formation. A mechanism of energy trapping in “uphill” doped crystals

Abstract Several examples of trapping of host electronic excitation energy by exciplex formation in “uphill” doped crystals (crystals containing only dopants of higher singlet excitation level than the host) are presented. The trapping mechanism in such systems is discussed. Exciplex formation in crystals is subject to the same electron donor-acceptor criteria as in solution, and requires no thermal activation or excess excitation energy. The exciplexes studied exhibit some structure in their low-temperature fluorescence.