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Surface modification of Co-doped ZnO nanocrystals and its effects on the magnet...
Pereira, A. S.; Ankiewicz, A. O.; Gehlhoff, W.; Hoffmann, A.; Pereira, S.; Trindade, T.; Grundmann, M.; Carmo, M. C.; Sobolev, N. A.A series of chemically prepared Co2+-doped ZnO colloids has been surface modified either by growing shells of ZnSe or by the in situ encapsulation in poly styrene . The surface modification effects using these two distinct chemical strategies on the magnetic properties of the nanocrystals were probed by electron paramagnetic resonance EPR . Structural characterization by means of x-ray diffraction and transmis...
Up conversion from visible to ultraviolet in bulk ZnO implanted with Tm ions
Monteiro, T.; Neves, A. J.; Soares, M. J.; Carmo, M. C.; Peres, M.; Alves, E.; Rita, E.We report on the up-converted ultraviolet near-band edge emission of bulk ZnO generated by visible and ultraviolet photons with energies below the band gap. This up-converted photoluminescence was observed in samples intentionally doped with Tm ions, suggesting that the energy levels introduced by the rare earth ion in the ZnO band gap are responsible for this process. ; FCT/FEDER - POCTI/CTM/45236/02 ; FCT/F...
Near-band-edge slow luminescence in nominally undoped bulk ZnO
Monteiro, T.; Neves, A.J.; Carmo, M.C.; Soares, M.J.; Peres, M.; Wang, J.; Alves, E.; Rita, E.; Wahl, U.We report the observation of slow emission bands overlapped with the near-band-edge steady-state luminescence of nominally undoped ZnO crystals. At low temperatures the time-resolved spectra are dominated by the emission of several high-energy bound exciton lines and the two-electron satellite spectral region. Furthermore, two donor-acceptor pair transitions at 3.22 and 3.238 eV are clearly identified in temper...
Photoluminescence and structure properties from microc-Si:H to microc-Si:H-PS
Ventura, P. J.; Cerqueira, M. F.; Carmo, M. C.; Ferreira, J. A.Microcrystalline and Porous on Microcrystalline Silicon thin films were produced. The photoluminescence characteristics of Porous on Microcrystalline Silicon were studied and compared with those from Microcrystalline and Porous Silicon grown on Silicon wafers. Under steady state it is possible to excite these samples with visible light at room temperature. This excitation gives rise to a red photoluminescence b...
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