A novel polymer electrolyte based on commercial poly(ethylene oxide), PEO, and europium picrate has been characterized by thermal analysis and measurements of total ionic conductivity. The results show that the observed conductivity is moderately high and independent of electrolyte composition, however, the use of this salt also imposes restrictions on thermal stability. Exploratory experiments suggest that the picrate anion increases the luminescent activity of the lanthanide cation and confirms that salt encapsulation within a polymeric host material reduces non-emissive energy loss. High molecular weight PEO is unlikely to be the best choice as a host polymer for use in optical applications as amorphous, homogeneous solid solutions were only obtained within a restricted composition range. (C) 2000 Elsevier Science Ltd. All rights reserved.