Infra-red Luminescence (Fluorescence) and Reflectance of Coals, Coal Derivatives and Graphite

Abstract

WE have investigated the infra-red luminescence (fluorescence) of coal and coal derivatives. Little, if any, visible luminescence is shown by coal except (1) in the presence of fluorescing minerals, and (2) in solutions of coal derivatives. Substances containing presumably large amounts of polynuclear aromatic compounds as well as large amounts of free radicals should exhibit appreciable visible luminescence. The lack of luminescence in solid coals or solid derivatives, such as coal-hydrogenation asphaltenes and pyridine extracts, can be explained on the basis of quenching due to various factors. But in the dissolution of asphaltene or coal extract, an intense light blue luminescence develops. A corresponding increase in specific absorption with dilution of coal-hydrogenation-asphaltene solutions was previously found and was correlated with an increase in free radicals, presumably formed by dissociation¹. The free radicals existing in solid coal may be of such a large size that luminescence missing from the visible could possibly exist beyond the visible range. With the development of a new method for determining infra-red luminescence², it has become possible to check coal and coal derivatives for luminescence in this region. Infra-red luminescence has now been observed.