Photoluminescence from 8-hydroxy quinoline aluminum embedded in porous anodic alumina membrane

By immersing porous alumina membranes in 8-hydroxy quinoline aluminum (Alq3) solutions, we embed Alq3 molecules into the nanovoids of the membranes. Photoluminescence (PL) spectral examinations show that the Alq3 molecules embedded in the alumina membrane show a blueshifted luminescent spectrum compared to that of Alq3 solid film. Since the blueshift of ∼18nm does not change with nanopore diameter, we consider it to be due to the confinement of nanovoids in the nanopore walls, which prevents Alq3 molecules from aggregation and thus weakens the interaction between them. Further spectral analyses suggest that the photogeneration of carriers takes place in oxygen vacancies at the surfaces of nanopore walls, whereas the radiative recombination occurs in the embedded Alq3 molecules. Förster energy transfer from oxygen vacancies to the embedded Alq3 molecules is proposed to be responsible for the enhancement of the PL intensity.