A medium emitting with a quantum yield independent of the excitation energy over a defined spectral range (e.g, concentrated rhodamine 6G solutions between 300 and 600 nm). Also used for devices producing an electrical signal proportional to the photon flux absorbed in a medium.
Sources:
Orange Book, 2nd ed., p. 193 (https://media.iupac.org/publications/analytical_compendium/)
PAC, 1984, 56, 231. 'Nomenclature, symbols, units and their usage in spectrochemical analysis-Part VI: molecular luminescence spectroscopy' on page 238 (https://doi.org/10.1351/pac198456020231)
PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2267 (https://doi.org/10.1351/pac199668122223)