Conversion of a green light emitting zinc-quinolate complex thin film to a stable and highly packed blue emitter film

Tris-(8-hydroxyquinoline) metal complex Znq2, used as light-emitting layer in electroluminescent (EL) devices was synthesized and optical properties of as-deposited Znq2 in thin films were studied. Interesting phenomenon was observed while studying the ageing and degradation behavior of Znq2 films and consequently a stable form having strong blue photoluminescence (peak 465 nm) was discovered. This converted (from green to blue emitting) film has higher molecular packing density and comparable photoluminescence intensity with Znq2 film. Here, we report on the production of this blue material under controlled conditions and its optical properties.The thin films have been deposited by thermal evaporation on quartz and silicon substrates. The optical constants (n and k) of green Znq2 film and converted (to blue) thin films have been determined using spectroscopic ellipsometry. Environment induced effects on optical properties of films have been studied using ellipsometry, photoluminescence and UV–vis transmission measurements.