Optical Gain in Semiconducting Polymer Nano and Mesoparticles
Abstract
The presence of excited-states and charge separated species was identified through UV and visible laser pump and visible/near-infrared probe femtosecond transient absorption spectroscopy in spin coated films of poly [N-9”-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) nanoparticles and mesoparticles. In the nanoparticle film, as for a uniform film of the pure polymer, charge formation is induced by UV excitation pump with a formation time of around 1 ps, while excitation of the low energetic absorption states (at 610 nm) induces in the nanoparticle film a large optical gain region reducing the charge formation efficiency. In the mesoparticle film, charge generation after UV excitation appears after around 50 ps, but little is observed after visible pump excitation. Optical gain in the mesoparticle films is observed after excitation at both 400 and 610 nm.
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