Electromodulation of photoluminescence in vacuum-evaporated films of fac-tris(2-phenylpyridine)iridium(III)

Electromodulation of photoluminescence (EML) has been investigated in vacuum-evaporated films of Ir(ppy)3 (tris(2-phenylpyridine)iridium) commonly used as a phosphorescent emitter in organic light-emitting diodes. The quenching of photoluminescence up to 30% is observed in the external electric field applied to sandwich cells Al/Ir(ppy)3/Al/glass. The electric field characteristics, the emission and excitation spectra of EML signals are interpreted in terms of field-induced dissociation of excited states into free and/or trapped charge carriers according to the Onsager theory. In addition, the existence of internal electric fields of (1-3) × 105 V/cm in Ir(ppy)3 films is inferred from the (1ω)EML signals measured at the first harmonic of the applied electric field frequency, in accordance with previous electroabsorption results.