SPIE Proceedings [SPIE 7th International Symposium on Advanced Optical Manufacturing and Testing Technologies (AOMATT 2014) - Harbin, China (Saturday 26 April 2014)] 7th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optoelectronics Materials and Devices for Sensing and Imaging - Effects of thermal annealing on photoluminescence spectra in π-conjugated polymer film: evidence for dual emission by temperature dependent measurements