Photon-Echo Relaxation Measurements with Two Dye-Lasers. Application to Pentacene-h14 and -d14 in p-Terphenyl-h14 Crystals at 1.5 K

Electronically controlled photon-echo relaxation measurements, using two nitrogen pumped dye-lasers, are reported for mixed crystals of pentacene-h14 and -d14 in p-terphenyl-h14 at 1.5 K. In dilute mixed crystals (ca. 10-8 M) the photon-echo lifetime is found to be exclusively determined by the fluorescence lifetime. Homogeneous linewidths of 7.1 and 5.9 MHz at 1.5 K are then calculated for the electronic origin of the 1B2u ← 1A1g transition of pentacene-h14 and -d14 respectively. The decrease in photon-echo lifetime at higher guest concentrations (ca. 10-7 M) is ascribed to energy transfer between excited and neutral guest molecules