Amplified spontaneous emission (ASE) characteristics of a green fluorescent dye (10-(2-benzothiazolyl)1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-[1] benzo-pyrano [6,7,8-ij]quinolizin-11-one) (C545T) encapsulated in a highly ordered three-dimensional (3D) inverted-opal titania (TiO2) photonic crystal (PC) microcavity were studied. Due to the utilization of a TiO2 PC, the emission spectrum was greatly narrowed and the ASE threshold, gain, and loss were significantly improved. The threshold, gain, and loss reached 1.25 mJ pulse(-1) cm(-2), 34.69 cm(-1), and 16.9 cm(-1), respectively The possible reason for the improvement in the ASE performance by the PC is attributed to the 3D photon localization by the microcavity effect of the PC. (c) 2008 Optical Society of America.