Revealing carbon mediated luminescence centers with enhanced lifetime in porous alumina

Carbon ion implantation mediated blue photoluminescence (PL) and the corresponding bluish white phosphorescence of anodic aluminum oxide (AAO) are presented. In particular, the observed 465 nm luminescence is found to be more sensitive to carbon, while its lifetime is raised to its maximum from 6.7 to 10.4 μs at a fluence of 1 × 10¹⁶ions/cm²_. The observed phenomenon seems to be associated with the formation of oxygen vacancy (V₀) via carbon ion enhanced modification of local AlO₆ octahedral symmetry, as revealed from X-ray absorption spectroscopy at O-K edge, and also consistent with X-ray photoelectron spectroscopy (XPS). Detailed XPS analysis indicates the preference of carbon at the Al sites, rather than at O for both octahedral and tetrahedral structures, and form C_Al cationic impurity, consistent with our density functional theory calculation. Further, carbon ion implantation driven enhanced PL lifetime is shown to be associated with energy transfer between V₀ and the vicinal C_Al. This work shows the potential of carbon doped AAO as a future candidate for developing rare earth free nontoxic phosphor.