The energy transfer to Er 3+ ions in a-Si 1-x C x : H films has been studied by absorption, luminescence and magnetic resonance spectroscopy. Erbium is incorporated either by magnetron assisted co-sputtering of Si and Er in a silane plasma or by conventional plasma deposition of a metalorganic compound which yields films of very different defect density and Er environment. The data confirm Er ions as efficient radiative recombination centres in a-Si : H, which are excited by resonant energy transfer from electron hole pairs in the host and disprove that dangling bonds are needed for emission at 1.5 µm wavelength by Erbium ions. We propose a Förster energy transfer, which is based on resonant dipole coupling. Resonance to excited states of Er 3+ is achieved as electrons thermalise in tail states and form pairs with localized holes and enables rapid energy transfer to Erbium ions while back transfer is inefficient due to lattice relaxation. Thermalisation and recombination rates in the host material control the excitation of Er ions and can be modified by alloying silicon with carbon.
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