Vol.:(0123456789) 1 3 Chemical Papers https://doi.org/10.1007/s11696-018-0404-z ORIGINAL PAPER Solid‑state fuorescence organic materials as a tool for spectral modifcation of ZnS‑based screen‑printed thick layer electroluminescence devices Michal Hrabal 1  · Ivaylo Zhivkov 1  · Lukáš Omasta 1  · Klára Foldýnová 1  · Patrícia Guricová 1  · Martin Vala 1  · Martin Weiter 1 Received: 31 October 2017 / Accepted: 24 January 2018 © Institute of Chemistry, Slovak Academy of Sciences 2018 Abstract This work is focused on modifcation 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 infuence of fuorophore was evaluated from the emission spectra of the electroluminescent device. Color space coordinates of emitted light of pure phosphor and phosphor modifed by DPP were plotted into the CIE space for better visualization of the color change. It was found that the presence of fuorophore increased the value of measured quantity—absolute spectral irradiance—more than seven times at 587 nm which corresponds to the maximum of fuorescence 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 modifcations of the phosphor. Keywords Electroluminescence · Phosphor · ZnS · Color conversion material · Fluorophore · Diketopyrrolopyrrole (DPP) · Alternating-current powder electroluminescence (ACPEL) · Fluorescence Introduction The effect of alternating-current electroluminescence (ACEL) of ZnS was frst observed by Georges Destriau in 1936 and such lighting devices based on ACEL were at frst considered as very promising new sources of light. This frst generation of devices did not show sufcient light output and also the life-time of original materials was very limited. All these factors ensured that ACEL light sources did not become commercially interesting at late 30s. It took almost 20 years to form basic concepts and frst theoretical back- ground of electroluminescence (Lehmann 1956; Howard and Lehmann 1954; Piper and Williams 1955). In the search for better performing device, new types of electroluminescence-based devices have been discovered in following time, namely DC (direct-current) thin flm electro- luminescence, DC powder luminescence, AC thin flm elec- troluminescence (ACTFEL) with sputtered or evaporated phosphor layer. Comprehensive review with specifc advan- tages/disadvantages of various approaches was given here (Chadha 1993; Bredol and Dieckhof 2010). These devices can be divided into two distinct branches: devices based on thin layer phosphor structure and those based on powder (thick layer) phosphors (ACPEL). The latter type is inter- esting for industrial usage since the preparation can be done by material printing on various substrates including fexible foils (Withnall et al. 2010; Wen et al. 2016). Material print- ing is well-established simple method for deposition of large areas which brings economical advantage among others compared to classical evaporation or sputtering deposition, which is typical for ACTFEL. Pioneering work has been conducted by Fischer where the process of generation of electroluminescence in doped ZnS phosphor has been clari- fed and later new models have been introduced by Fischer This work was presented at the 81st Prague Meeting on Macromolecules held on September 10–14, 2017. * Michal Hrabal xchrabalm@fch.vut.cz 1 Faculty of Chemistry, Brno University of Technology, Purkyňova 464/118, Brno, Czech Republic