Impurity induced phosphorescence in anthracene crystal

The phosphorescence spectra of 'pure' anthracene crystals and crystals containing trace amounts of 2-methylanthracene, 2-hydroxyanthracene and 2-aminoanthracene are reported, together with prompt and delayed fluorescence spectra. In the 'pure' crystals delayed fluorescence and phosphorescence excited by 337 and ≈ 400 nm radiation are weaker by an order of magnitude or more than in crystals with traces of impurities. With 2-methyl- and 2-hydroxy-anthracene as dopants, the phosphorescence origin is shifted by 132 cm−1 and 73 cm−1 respectively from the pure anthracene exciton origin. In both the emission is characteristic of anthracene host molecules acting as 'X' traps. 2-amino-anthracene as dopant gives an emission with origin displaced by 311 cm−1. In this case the dopant is the emitter, and thus acts as a chemical trap. The two impurity induced 'X' traps are close in energy to traps recently assigned to structural defects. However no significance is as yet placed on this result.