Pulse-shaped emissions with time delay in single crystals of thiophene/phenylene co-oligomers

Emission dynamics of the organic semiconductor material thiophene/phenylene co-oligomer (TPCO) single crystals has been studied under high-density optical excitation at 5 K. The optical amplification phenomenon is observed both on 0-1 and 0-2 vibration transitions, where these intensities increase superlinearly with the increase in excitation density. In particular, when optical amplification has started, the 0-1 emission line shows symmetric pulse-shaped emission and its pulse peak has delay time of 50 ps. Delay time and pulse width decrease with the increase in excitation density. The excitation density dependence of delay time is useful for optical devices with the variable delay time with amplification.