100% fluorescence efficiency of 4,4′-bis[(N-carbazole)styryl]biphenyl in a solid film and the very low amplified spontaneous emission threshold

Abstract
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 E th = 0.32 ± 0.05 μ J ∕ cm 2 . We observed that the 6 wt %-BSB-Cz:CBP film has an ultimate photoluminescence(PL) quantum efficiency of ϕ PL = 100 % and a short transient lifetime of τ f = 1.0 ± 0.1 ns , leading to a large radiative decay rate of k r = 1 × 10 9 s − 1 . We demonstrated that the extremely low ASE threshold originated from the large radiative decay rate of BSB-Cz.