Erbium-implanted silica colloids with 80% luminescence quantum efficiency

Silica colloids with a diameter of 240–360 nm, grown by wet chemical synthesis using ethanol, ammonia, water, and tetraethoxysilane, were implanted with 350 keV Er ions, to peak concentrations of 0.2–1.1 at. % and put onto a silicon or glass substrate. After annealing at 700–900 °C the colloids show clear room-temperature photoluminescence at 1.53 µm, with lifetimes as high as 17 ms. By comparing data of different Er concentrations, the purely radiative lifetime is estimated to be 20–22 ms, indicating a high quantum efficiency of about 80%. This high quantum efficiency indicates that, after annealing, the silica colloids are almost free of OH impurities. Spinning a layer of polymethylmethacrylate over the silica spheres results in an optically transparent nanocomposite layer, that can be used as a planar optical waveguide amplifier at 1.5 µm that is fully compatible with polymer technology.