A Phosphorescence Demonstration In teaching photochemistry, or occasionally analytical or physical chemistry, it is instructive to demonsbrate the processes of fluorescence and phosphorescence. Fluorescence is conveniently demonstrated with quinine water (tonic), but choice of a phosphorescent compound is more difficult. We find biphenyl nearly ideal for this purpose. The phosphorescence of this readilyavailable compound is easily visible (450-500 nm, +* 0.2) and long-lived (r,4.5-5.1 sec), and is 0.2).' not obscured by absorption (max. 248 nm) or fluorescence (max. 320 nm, +, For the demonstration, a few crystals (1-2 mg) of practical grade biphenyl ore dissolved in 10 M. A few milliliters of this solution are ml of absolute ethanol to give a solution ahout placed in a quartz tube, and the tube is sealed with a serum cap. Nitrogen is bubbled through the solution for 5-10 min. This solution at room temperature gives no visible fluorescence or phosphorescence. The tube is partially immersed in liquid nitrogen until a. rigid glass is farmed (about 1.5 min); rigidity of the glass o m be checked by tipping the tube. The ethanol glass may crack, but this does not affect the demonstration. The tube is removed from the liquid nitrogen and irradiated with a source of 254nm ultmviolet radiation (a short-wavelength thin-layer chromatogram viewer is ided) for a few seconds, then the lamp is removed. The bluish-white phosphorescence is visible for 10-15 sec in a partially-darkened small lecture room. The sample warms rapidly and must he cooled again before repeating the demonstration. Naphthalene can also be used for this demonstration, but the phosphorescence is weaker and shorter-lived.
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'P~RKER,C. A., "Photoluminescence of Solutions," Elsevier, Amsterdam, 1968, pp. 92 and 281. GERALD L.GOE OF NOTREDAME UNIVERSITY NOTREDAME.INDIANA 46556
41 2 / Journal o f Chemical Education
