Spectrally narrow emission from organic films under continuous-wave excitation

The authors observed a narrow emission from a 500-nm-thick codeposited organic thin film, 6wt% 4,4′-bis[(N-carbazole)styryl]-biphenyl (BSB-Cz) doped into a 4,4′-bis(N-carbazole)-biphenyl host, under continuous-wave excitation. Although they observed no clear threshold characteristics on the spectral narrowing, they found that the emission centered at a wavelength of λASE=462nm, corresponding to the zero to one transition of BSB-Cz, has a transverse electric mode with a narrow full width at half maximum of λFWHM=3.4nm, indicating the occurrence of amplified spontaneous emission. No excited state absorptions of singlet and triplet excited states of BSB-Cz are confirmed around λASE, leading to large net gain for the light amplification.