Eu(III) complexes with chosen Keggin polyoxomatalates, POM, containing organic counter cations (tetrabutylammonium, tetrabutylphosphonium, triphenylethylphosphonium), were synthesized, and their photophysical properties were studied. The synthesized complexes had the general formula of XnH5-n[EuSiW11O39], formulated based on the results of elemental and thermogravimetric analysis and FTIR spectroscopy. The photophysical properties of the obtained compounds were investigated using photoluminescence and electro- chemiluminescence, ECL, methods in solutions and solids. The most intense luminescence of Eu(III) was observed for the complexes with tetrabutylammonium cations. After the addition of phenanthroline to the XnH5-n[EuSiW11O39] solutions, a large increase in the Eu(III) lumi- nescence intensity and a lengthening of its luminescence lifetime were observed as a result of the formation of ternary complexes. Attempts to apply ECL as a method of light emission by generating species capable of forming excited states in Ln/POMs, i.e., Tb(III) and Eu(III) in the Na9EuW10O36 and Na9TbW10O36 complexes, were made. The influence of the POM complexes on the ECL was also tested using the Tb/EDDHA (EDDA=ethylenediamine di(o-hydroxyphenylacetic acid)) complex, which is effective in generating ECL. The synthesized complexes had the general formula of XnH5-n [EuSiW11O39], formulated with selected Keggin polyoxomatalates, POM, containing organic counter cations (tetrabutylammonium, tetrabutylphosphonium triphenylphosphine), synthesized, and their photophysical properties were studied based on the results of elemental and thermogravimetric analysis and FTIR spectroscopy. The photophysical properties of the obtained compounds were investigated using photoluminescence and electro- chemiluminescence, ECL, methods in solutions and solids. The most intense luminescence of Eu (III) was observed for the complexes with tetrabutylammonium cations. After the addition of phenanthroline to the XnH5-n [EuSiW11O39] solutions, a large increase in the Eu (III) lumi- nescence intensity and a lengthening of its luminescence lifetime were observed as a result of the formation of ternary complexes. Attempts to apply ECL as a method of light emission by generating species capab The influence of the POM complexes on the ECL was also tested using the Tb / EDDHA (EDDA (dDA) = ethylenediamine di (o-hydroxyphenylacetic acid)) complex, which is effective in generating ECL.