Temperature-dependent electroluminescence from (Eu, Gd) coordination complexes

Light emission from single-layered electroluminescent devices is described in which (Eu, Gd) coordination complexes, ${\mathrm{(Eu}}_{\mathrm{0.1}}{\mathrm{Gd}}_{\mathrm{0.9}}{\mathrm{)(TTA)}}_{\mathrm{3}}{\mathrm{(TPPO)}}_{\mathrm{2}},$ and electron transport material oxadiazole derivative, 2-(4-biphenyl)-5-(4-t-butylphenylyl)-1,3,4-oxadiazole, are dispersed in a hole-transporting host polymer poly(N-vinylcarbazole) film. The color of the emitted electroluminescence changes smoothly from green-white to red with temperature varying from 77 to 300 K. This phenomenon is discussed in terms of temperature dependent yields of phosphorescence from the triplet state of the Gd and Eu chelates and the intermolecular energy transfer from Gd-chelate to Eu-chelate cages.