Electroluminescence of Light- Emitting Organic Semiconductor/ Europium Oxide Nanoparticle Hybrid Junction

Abstract

A hybrid nanoparticles light emitting diode (NPs-LED) was fabricated as layers of ITO/TPD:PMMA/ Eu₂O₃ / Alq₃ / Al, by phase segregation method using spin coating technique. The NPs-LED hybrid device emitted light and consisted of three layers in a definite order placed on the transparent conducting oxide as an ITO substrate; the first layer was made of (N, N'-bis (3-methylphenyl) -N, N'-bis (phenyl) benzidine) (TPD) and polymethyl methacrylate (PMMA) polymers combined together. The second layer consisted of Europium (III) oxide (Eu₂O₃), while the third  layer was Alq₃, one of the most frequently-used electron transport layers.

The electroluminescence (EL) of NPs-LED was studied with different bias voltages (20, 25 and 30V) at room temperature. Depending on the CIE 1931 color spaces, X the white light was generated at 30V and the green light at 20V. This was achieved by benefitting from the transition between deep levels in the energy gap of Eu₂O₃ NPs (surface state ) and magnetic dipole transition for Eu⁺ (⁵D_0-3and⁵L₆ to ⁷F_0-6). The Current – Voltage (I-V) characteristics demonstrated that the current varies with voltage and that the knee voltage value is 5 V. The EL spectrum showed a broad band emission, with a range of 350 - 700 nm. Finally, the correlated color temperature (CCT) was found to be about 7100 to 11500k.