Spectrally separated optical gain and triplet absorption: Towards continuous wave lasing in organic thin film lasers

We studied laser dynamics of poly(9,9′-dioctylfluorene) (PFO) based organic thin films lasers. The favorably used host/guest system PFO, containing 6,6′-(2,2′-octyloxy-1,1′-bianphthalene) binaphthyl spacer groups (BN-PFO), doped with 1,4-bis(2-(4-(N,N-di(p-tolyl)amino)phenyl)vinylbenzene (DPAVB) shows a dramatic decrease of laser emission for excitation pulses longer than a few nanoseconds, whereas the undoped material offers a stable emission. By measuring the optical gain and the triplet absorption spectra we show that the spectral overlap of the two spectra leads to a dramatic increase of the laser threshold in the doped system due to a pile-up of long lived triplet states. On the contrary for BN-PFO, optical gain and triplet absorption are found to be spectrally separated. As a result, accumulated triplet excitons hardly affect the laser emission.

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► Quasi cw lasing in PFO based organic semiconductor lasers is explained by spectrally separated gain and triplet absorption.
► Spectro-temporal behavior of diode pumped lasers based on doped PFO are studied.
► Overlapping photo-induced absorption and material gain spectra lead to a dramatic decrease of conversion efficiency.
► Material gain and photo-induced absorption measured with high sensitivity in a waveguide structure.