Spontaneous emission of radiation from an electronically or vibrationally excited species not in thermal equilibrium with its environment.
See also: bioluminescence, chemiluminescence, electro-generated chemiluminescence, fluorescence, phosphorescence, photoluminescence, radioluminescence, sonoluminescence, thermoluminescence, triboluminescence.
PAC, 1996, 68, 2223 (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2252
PAC, 1994, 66, 2513 (Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994)) on page 2522
See also:
Orange Book, p. 184
Orange Book, p. 231
PAC, 1990, 62, 2167 (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2200