We　investigate　the　dependence　of　the　optical　spectral　properties　of　the　exciplex　in　the　polymer　blend　of　Poly　(9,　9＇-dioctylfluorene-co-　benzothiadiazole)　(ADS133YE)　and　poly　(9,9＇-dioctylfluorene-co-bis-N,　N＇-(4-butylphenyl)-bis-N,N-　phenyl-1,4　-　phenylenediamine)　(ADS232GE)　on　the　excitation　wavelengths　and　on　the　composite　ratios　between　these　two　materials.　By　controlling　the　excitation　wavelength,　the　energy　transfer　can　be　optimized,　which　favors　the　formation　of　the　exciplex　on　the　interface　between　the　two　blend　phases.　Furthermore,　changing　the　composite　ratio　acutally　modifies　the　mophorlogy　of　the　blend　film,　modifying　the　excited　states　on　the　interface　and　giving　the　microscopic　insights　into　the　mechanisms　of　the　exciplex　emission.　These　investigations　are　important　for　better　understanding　the　physics　of　the　heterojunction　structures　in　the　polymer　blends　and　is　thus　helpful　for　the　design　of　organic　photovoltaic　devices　©2009　SPIE-OSA-IEEE.