Pulse-Shaped Emissions with Time Delay in Single Crystals of Thiophene/Phenylene Co-Oligomers

Abstract

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.

Optical selection rule for the lower Davydov excitons in co-oligomer single crystals

“…These BPnT crystals exhibit good electrical properties, 21 and inter-esting optical phenomena such as high-gain amplified spontaneous emission, [22][23][24] lasing by a self-formed cavity, 25,26 and pulselike emission with a time delay suggesting superfluorescence. 27 These optical phenomena are observed in BPnTs whose structures differ slightly from those of OTs. Thus, drastic changes to the optical properties can be effected by making slight changes to their structures.…”

Gain‐narrowed emissions of thiophene/phenylene co‐oligomer single crystals

“…The polarization of SRRS from a single crystal of BP1T could not be explained by anisotropic orientation of the constituent molecule but was interpreted by coherent molecular vibration over the crystal [6]. Furthermore, it was recently reported that a vapor-grown single-crystal of BP1T showed pulse-shaped emissions with time delay of several tens of ps under high density pulse excitation at 5 K [7]. The occurrence of these peculiar emissions might be suggestive of a cooperative process such as super-fluorescence (SF) [8][9][10].…”

Optically pumped lasing from vapor‐grown crystals of methoxy‐substituted thiophene/phenylene co‐oligomer

“…Moreover, pulse‐shaped emission with time delay of 50 ps has been reported for single‐crystal 2,5′‐bis(4‐biphenylyl)‐thiophene (BP1T) 12 and discussed in terms of the cooperative light amplification phenomenon. Subsequently, prethreshold laser oscillations accompanied with longer delay time up to 300 ps have been observed at room temperature for single‐crystal 2,5‐bis(4′‐methoxybiphenyl‐4‐yl)thiophene (BP1T‐OMe) which has methoxy groups at the molecular terminal of BP1T 13 Such a pulse‐shaped emissions with delay time has been reported for O doped KCl crystal at low temperature as known as superfluorescence based on cooperative excitonic interactions in the system 14, 15.…”