Fluorescence of Solid Anthracene

THE fluorescence of solid anthracene in light of wave-length 3650 A. is changed from blue to green when very small quantities of naphthacene are present in solid solution. This is explicable by an 'exciton' mechanism whereby energy is handed on by resonance from molecule to molecule1. The graphs shown here represent a quantitative examination of the effect, the blue and green components of the fluorescence being measured by a photo-cell through Ilford filters 601 and 404 respectively. The upper graph shows for two temperatures the fall of the blue anthracene fluorescence and the rise of the green naphthacene fluorescence with concentration of the latter, expressed as quantum efficiencies with a probable error of 15 per cent. The emissions are about equal at a naphthacene concentration of 3 × 105, and the green reaches a maximum at about 103. Above this concentration the colour of the emission changes to yellow as for pure naphthacene, and the efficiency decreases, evidently due to the overstepping of the limits of solid solution.