Luminescence from Si nanocrystal grown in fused silica using keV and MeV beam

Embedded nanocrystals are grown using both keV and MeV energy ion beam followed by thermal annealing. Initially, 200 keV Si+ ions were implanted in fused silica at various fluences varying from 2.5×1015 to 2.5×1016 ions cm−2. A set of the implanted samples were irradiated using 70 MeV Si-beam and annealed at 900 °C for 3 h in nitrogen atmosphere. Photoluminescence (PL) studies were carried out by exciting the samples at room temperature with 514 nm line of an Ar ion laser. Implanted, irradiated and annealed samples showed a PL peak at 568 nm, whereas implanted and annealed samples had a PL peak at 580 nm. 70 MeV Si ion irradiation created tracks of about 2 nm diameter along its trajectory due to inelastic collision process. Nanocrystals are expected to be formed along the trajectory due to dense electronic excitation created by MeV Si beam around the tracks and subsequent annealing. The blue shift observed is attributed to quantum size effect in which reduction of the average nanocrystal size leads to emission at a shorter wavelength. The formation of Si nanocrystals has also been confirmed by complementary studies of UV-visible absorption spectra. Sharp absorption edges between 230 and 270 nm due to formation of Si nanocrystals were observed.