Origin of nanopore alumina film photoluminescence: three kinds of defect centers

Abstract

Nanopore alumina films (PAF) are fabricated by two-step anodic oxidation of aluminum in oxalic acid. The field emission scanning electron microscope measurement reveals the surface microstructure of PAF, and the defect formation mechanism in PAF is analyzed. The energy dispersive X ray spectroscopy and the Fourier transform infrared spectroscopy results indicate that oxalic ions are incorporated into the PAF in the synthesis process and further heating up to 500 ℃ does not cause oxalic ions to completely decompose. The photoluminescence (PL) spectra of PAF can be divided into three bands by Gaussion fitting method. The measurement results and the defects in PAF show that the PL originate from optical transitions of two kinds of different oxygen-deficient defect centers (F and F+) and oxalic impurities related defect center, PL centered at 402, 433 and 475 nm, respectively. We put forward for the first time that F centers play a leading role. The PL characteristics of the PAF prepared in oxalic acids with different concentrations suggest that three kinds of the luminescent center positions do not change with the increase of the oxalic acid concentration, but their relative intensities change with the increase of the oxalic acid concentration, i.e., F and F+ decrease, oxalic impurities related defects increase, and these will cause the PL peak position to be red-shifted. Finally, we put forward that the oxalic impurities in PAF can be changed by controlling the concentration of oxalic acid. The present experiments and results will be beneficial to the understanding of light-emitting mechanism in PAF, meanwhile, in this paper we propose a new train of thought for PAF preparation application.