Fluorescence properties of europium(II) and other divalent metal ion doubly-doped poly(methacrylate containing 15-crown-5 structure) complexes

Abstract

Eu 2+ and an alkaline earth metal ion: Mg 2+, Ca 2+, Sr 2+, and Ba 2+, or a Group IIB metal ion: Zn 2+ and Cd 2+, doubly-doped poly(methacrylate containing 15-crown-5 structure) complexes were prepared. Their fluorescence properties were investigated in the solid state and compared to those of an Eu 2+ only-doped polymer complex. Under UV irradiation, blue emissions based on the electric transition of the Eu 2+ ions in the Eu 2+−15C5 moiety complexes are observed for all the polymer complexes. The maximum fluorescence intensity obtained for the Eu 2+−Zn 2+ doubly-doped polymer reaches c. 50% of that for CaWO 4:Pb (NSB1026), whereas the emission intensity of the polymer containing Eu 2+ alone was at most c. 20% of that of NSB1026. The emission intensity for the Eu 2+−M 2+ doubly-doped polymer (MMg, Ca, Sr) is almost the same value as that for the Eu 2+ only-doped one. All the doubly-doped polymers as weil as the Eu 2+ only-doped one indicate concentration quenching. The concentration quenching is suppressed to some extent by the presence of the metal ions: Mg 2+, Ca 2+ and Sr 2+, since the maximum of the emission intensity shifts to the higher EuCl 2 concentration side for these doubly-doped than for the Eu 2+ only-doped samples. The Eu 2+−Ba 2+ doubly-doped polymer gives the smallest emission intensity of all the alkaline earth codoped ones. The bulky Ba 2+ ions would influence the surroundings of the Eu 2+−15C5 moiety complexes and/or interfere with the complexation. By codoping with Zn 2+, the luminescence lifetime of Eu 2+ is apparently lengthened. This behavior is not observed in the case when using the alkaline earth ions as codopant ions. These results suggest that the way Zn 2+ is present in the polymer, is different from the alkaline earth metal ions. The latter ions are present in the polymer as complexes with 15-crown-5. On the other hand, for the Eu 2+−Zn 2+ doubly-doped one, ZnCl 4 2− complex anions are formed in the polymer matrix, confirmed by Raman spectroscopy. Temperature dependent reciprocal magnetic susceptibilities for the Eu 2+ only-doped and Eu 2+−Zn 2+ doubly-doped polymers indicate antiferromagnetic interactions and the interatomic distances of the Eu 2+ ions are discussed on their asymptotic Curie points. For the Eu 2+−Cd 2+ codoped one, it also indicates a higher maximum emission intensity than for the Eu 2+ only-doped one. An Eu 2+−Hg 2+ doubly-doped polymer was not available. The formation of the halogeno complex anions significantly affects the fluorescence properties.