ELECTROLUMINESCENCE CELL-BASED ON POLYOXOMETALATES - PULSED ELECTRIC-FIELD-INDUCED LUMINESCENCE OF DECATUNGSTOEUROPATE DISPERSION LAYERS

ITO/[EuW10O36]9-/Mylar/ITO electroluminescence (EL) cells have been fabricated with the [EuW10O36]9- layer with 40-80 mum thickness, as the emissive medium. The spectral distribution of EL, induced by the applied negative voltage pulse, indicates the presence of three emission envelopes of nitrogen plasma, oxygen-to-tungsten (O --> W) ligand-to-metal charge transfer (LMCT) emission, and Eu3+ f-f emission for every dispersion layer of Ca2+, Sr2+, or Ba2+ salt of [EuW10O36]9- and Na9[EuW10O36] . 32 H2O pellet. The Eu3+ EL lines are similar to Eu3+ photoluminescence lines but with relatively higher intensity in the 5D0 --> F-7(2) transition. Typical operating conditions are -0.7 approximately 1.2 kV at 100-300 Hz. A high porosity of the [EuW10O36]9- layer which allows a voltage drop to occur in the layer, resulted in a significant contribution of the nitrogen plasma to the total emission. Comparison of transient behaviors among three emissions exhibits an accumulation of charges inside the [EuW10O36]9- layer which induces an internal field. Such charges once trapped are released and accelerated by external field or by internal field after the applied pulse is turned off, until enough kinetic energy is acquired to excite [EuW10O36]9-. The insulating Mylar film is important for the EL in that it allows accumulation charges to remain inside the [EuW10O36]9- layer. The EL intensity is still very low, due to the small number of internal carriers and the small amount of carrier accumulation in the vicinity of the [EuW10O36]9-/Mylar interface.