exciton absorption

https://doi.org/10.1351/goldbook.14009
Absorption of ultraviolet, visible, or infrared radiation yielding optical information on the excitons in solids. Exciton absorption bands in a spectrum of a semiconductor or insulator are located on the long wavelength side of the fundamental absorption edge.
Source:
PAC, 2011, 83, 931. (Glossary of terms used in photocatalysis and radiation catalysis (IUPAC Recommendations 2011)) on page 951 [Terms] [Paper]