Time domain spectroscopic study of PL decay in zinc benzothiazole suitable for white light emitting OLEDs

There has been a keen interest in metal benzothiazoles, and specifically for zinc benzothiazole for applications involving broad emission such as white light organic light emitting diodes. The broad emission characteristic is normally attributed to occurrence of exciplexes and is believed to further broaden in electroluminescence from a bilayer device. In order to understand possible role of molecular level interaction in photoluminescence (PL), we study PL decay dynamics of zinc benzothiazole powder, thin film and a virtual alloy with a hole transport material TPD (prepared by stacking very thin alternate layers of the two materials). We observe significant hastening of the PL decay from powder and 'effective alloy' to the thin film. To unravel the nature of changes in decay dynamics, we employ both least square fitting, and time domain spectroscopy known as time analyzed transient spectroscopy (TATS). The efficacy of the later procedure in obtaining insights is demonstrated. Our results indicate that inter molecular interaction in the condensed phase significantly influence the life time of the radiative species in this material.