Luminescence and structural studies of iron implanted α-Al2O3

Abstract

Transition metal ions (TM) are typically contaminants of growth processes in wide band gap materials. In Al2O3 (Eg ∼ 9 eV) Cr, Fe and Ti are responsible for red, yellow and blue colored sapphire. While the R-lines from Cr3+ have been extensively studied by photoluminescence (PL) the optical characterization of other transition metal ions is less known. In this work we studied by PL, transmission electron microscopy (TEM) and RBS/channeling measurements a series of iron implanted α-Al2O3 samples. In the red region a sharp emission line at 1.833 eV with a lifetime of ∼1 ms is identified at low temperature. For temperatures above 35 K and on the high energy side a new thermally populated emission line occurs at 1.843 eV. Structural analysis performed by RBS/channeling, TEM and X-ray measurements indicates that metallic iron precipitates as well as iron oxide complexes are present in the samples. Combining the temperature dependence of luminescence and decay times with the results obtained from structural analysis a model for the optical center is discussed.