Photoluminescence and Stoichiometry Correlation in Nanocrystalline EuO _x Thin Films: Tunable Color Emission

The development of broadband and ultracompact optoelectronic devices relies on the possibility of fabricating bright and tunable emitters at the nanoscale. Here, we show emission from EuO _x (1 ≤ x < 1.4) thin films on silicon formed by nanocrystals with average sizes in the range of 5 nm. The photoluminescence emission of the nano-EuO _x films is tunable as a function of the oxygen concentration changing from a green broadband Eu²⁺-related emission to a narrow red Eu³⁺-related emission. To reach these results has been instrumental through the use of a new methodology specially designed to achieve high-quality europium oxide films whose compositional properties are controlled by the growth base pressure and preserved thanks to a chemically stable and transparent cover layer of Al₂O₃. Our findings confirm the outstanding potential of nanostructured EuO _x films as "one-compound" optical elements with tunable emission properties for their implementation in integrated silicon-based devices.