Crystallization and interdiffusion of organic layers have been widely considered to be important causes for performance degradation of organic electroluminescent devices. By using high substrate temperature during vapor deposition, we have fabricated organic electroluminescent devices with crystalline organic layers. Contrary to the common belief, substantial increases in luminescent efficiency and brightness have been observed in the device thus fabricated. Such devices also showed much improved storage stability against high humidity compared to the conventional ones with amorphous organic layers.

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Luminance-current characteristics of organic electroluminescent devices based on the europium complex of europium(dibenzoylmethanato)3 (bathophenanthroline) (Eu(DBM)3bath) have been investigated. Transient measurements were carried out to study the decay process of excited Eu3+ ions. A comparison of experimental data and theoretical calculation shows that biexcitonic quenching among the excited Eu3+ ions is an important channel in their decay process, and this quenching process is a primary cause for our observation of a rapid decrease in quantum efficiency with increasing current density. Extending the recombination zone is found to be beneficial to reducing this defective effect. The mechanism of the quenching process is also discussed.