Rare Earth Luminescence in Nanostructured Amorphous Silicon Alloys

摘要

Rare Earth (RE) doped amorphous silicon alloys can be prepared by reactive RF sputtering from a Si target partially covered with metallic or oxide RE platelets using appropriate reactive atmospheres. We have studied Er~(~(3+)), Nd~(3+), Eu~(3+) and Tb~(3+) in a-Si:H, a-SiO_x:H and a-SiN_x:H. Annealing optimizes the photoluminescence and can induce the formation of Si nanocrystals. The RE act as nucleation centers. The RE ions present intense photoluminescence at room temperature. EXAFS measurements reveal a highly non-centrosymetric lattice site for Er in a-SiO_x:H. This partially breaks the selection rule that forbids intra-4f transitions. The RE present two luminescence lifetimes, the fast component determined by the host and the slow component associated to the local symmetry of the ions. The amorphous and nanostructured hosts increase the cross section for RE excitation by a few orders of magnitude, making the materials practical for applications as phosphors and active amplifiers.