The Optical Absorption of Anthracene Crystal near 4000 A

Abstract

The absorption spectrum of anthracene single crystal was measured in the range from 3950 A to 4400 A, i. e., the long wave-length tail of A_1g–B_2u transition. For the change of temperature from −180°C to 80°C, the absorption increases markedly both for a- and b-polarized light. The contour in the absorption tail can be separated into two parts. The one is the absorption obeyed to the Urbach rule, and the other is the absorption due to the transition from the hot level in the ground state to the first excited state. In the former absorption at a temperature Range above −80°C, the constant values of σ in the Urbach formula are obtained; 1.68 in a-polarized light and 0.88 in b-polarized light. In the latter absorption, the peaks at 4125 A and 4145 A were observed with a- and b-polarized light, respectively. The common thermal activation energy of 0.16 eV is obtained.