In an emission experiment, an apparent decrease in emission quantum yield and/or distortion of bandshape as a result of reabsorption of emitted radiation.
During a light irradiation experiment, absorption of incident radiation by a species other than the intended primary absorber.
Source: PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2247 (https://doi.org/10.1351/pac199668122223)