Erbium-doped thin amorphous carbon films prepared by sputtering

The optical gap of hydrogenated amorphous carbon (a-C:H) can be modulated in the 0.5 -3.5 eV range depending on the deposition conditions. This feature could be used for the development of light emitters when this host is doped by rare earth ions. In this paper we present some preliminary results concerning erbium ions embedded in a thin amorphous carbon film. Erbium activated a-C:H-films were deposited at room temperature on silica substrates by magnetron co-sputtering a graphite target together with metallic erbium pieces in an Ar+C6H12 gas mixture. Different sputtering conditions, in terms of applied power and C6H12 partial pressure, allowed to obtain C-matrices characterized by different optical band gaps. X-ray Photoelectron Spectroscopy (XPS) was performed to determine the chemical state of erbium and the dependence of the erbium concentration on the deposition conditions. The erbium concentration was varied from 0.15 at % to 0.8 at %. The optical and spectroscopic properties of a-C:H-films were studied in relation to the parameters of the deposition process. Band gaps ranging from 1.5 to 0.5 eV was estimated from absorption spectra applying the Tauc model. The sp2/sp3 fraction in the films, as derived from the X-Ray induced C KVV Auger spectrum, is compared to their energy gap. Photoluminescence measurements in the region of the 4I13/2 ? 4I15/2 transition of the Er3+ ion were performed by exciting at various wavelengths the different films. Although further work is needed to improve the films with respect to their photoluminescence properties, this work open new perspectives regarding the possibility to exploit the properties of rare earth-doped amorphous C networks as luminescent systems.