Solid-state fluorescence organic materials as a tool for spectral modification of ZnS-based screen-printed thick layer electroluminescence devices

This work is focused on modification of spectral characteristic of light emitted by alternating current powder-based ZnS electroluminescent device by addition of a color conversion material. A suitable diketopyrrolopyrrole (DPP) derivative with absorption spectrum compatible with emission spectrum of phosphor was found and was added into the printing formulation. Electroluminescent panel was printed by screen printing method and the influence of fluorophore was evaluated from the emission spectra of the electroluminescent device. Color space coordinates of emitted light of pure phosphor and phosphor modified by DPP were plotted into the CIE space for better visualization of the color change. It was found that the presence of fluorophore increased the value of measured quantity—absolute spectral irradiance—more than seven times at 587 nm which corresponds to the maximum of fluorescence emission of DPP. This approach provides useful tool to obtain colors of various wavelengths and therefore various hues without the need to look for new challenging and expensive chemical modifications of the phosphor.