Broad emission spectral enhancement of polyfluorene copolymer by coupling to assembled plasmonic crystal of silver nanocubes

•Silver nanocubes with 55 nm and 100 nm are assembled into plasmonic crystals.•Conjugated polymer exhibits 10-fold emission enhancement on plasmonic crystal.•The rate enhancement shows both nanocube size and wavelength dependence.•The maximum Purcell factor of 4.5 are found near the emission peak of polymer. The plasmonic enhancement of conjugated polymer (CP) based light-emitting device calls for large scale and high quality plasmonic crystals (PlCs). Herein, silver nanocubes with diameters of 55 nm and 100 nm have been respectively assembled into closely packed PlC-55 and PlC-100 through oil-water interfacial assembly method. By coupling with the PlCs, the photoluminescence (PL) of polyfluorene copolymer can be enhanced in a broad range of excitation and emission wavelengths, exhibiting over 10-fold enhancement in PL intensity as the PlC-CP separation is controlled at 11 nm by using polyvinylalcohol as a spacer. The Purcell factors of CPs show both particle size and emission wavelength dependence, where the maximum value of 4.5 are found in CPs that are placed on PlC-100 at wavelengths near the CP emission peak.