We examined the amplified spontaneous emission (ASE) characteristics of fluorescent styrylbenzene derivatives doped into a 4, 4′ -di(N-carbazolyl)biphenyl (CBP) host. In particular, 4, 4′ -bis[(N-carbazole)styryl]biphenyl (BSB-Cz) demonstrated an extremely low ASE threshold of Eth =0.32±0.05 μJ cm2. We observed that the 6 wt %-BSB-Cz:CBP film has an ultimate photoluminescence (PL) quantum efficiency of φPL =100% and a short transient lifetime of τf =1.0±0.1 ns, leading to a large radiative decay rate of kr =1× 109 s-1. We demonstrated that the extremely low ASE threshold originated from the large radiative decay rate of BSB-Cz.
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