Effect Of Ion Implantation On Spectral Properties Of YSZ And Al₂O₃ Single Crystals

Ion implantation is an important technique of modifying the surface properties of materials. YSZ (yttria-stabilized zirconia) and a-Al2O3 single crystals are two high quality ceramic materials. The former has excellent stability and the latter has poor stability under irradiation. The studies on optical properties and irradiation effect of heavy ion implanted samples are very important from both theoretical and applied view points.In this work, the optical properties and defect structures in Xe+-implanted YSZ and Ni+-implanted Al2O3 were studied by using optical spectroscopy, TEM, XPS and TRIM 96 calculation. It was found that1) A broad absorption band centered at 522 nm was observed in 1×1016 cm-2 Xe+-implanted YSZ. The band was previously associated with F-type color centers and V-type color centers, as analyzed in X-ray irradiated YSZ sample. However, the absorption band observed in our experiments has a shift towards the longer wavelength (red shift) as comparing with that in the X-ray or neutron irradiated YSZ spectra. This shift may mainly due to large local distortions near the F-type centers and the V-type centers and the presence of multiple color centers.2) Luminescence spectra of a 1 × 1016 cm-2 Xe+-implanted YSZ show that broad emission bands ranging from 400nm to 600nm, in agreement with the results of r-ray and neutron-irradiated YSZ. The absorption band shifts towards the shorter wavelength (blue shift), i.e., 497 nm at dose of 1 × 1017 Xe+cm-2. And no luminescence emission band was observed under an excitation wavelength of 250-370 nm.3) TEM images show that the densities of the defect clusters increase with the increasing fluences. As more Xe+ was implanted in YSZ samples (>1017 cm-2), the increase of the densities becomes to be very slow. In addition, a large number of bubbles, 3-5 nm in diameter, precipitated after a fluence of 1×1017 Xe+cm-2. The blue shift could be associated with precipitation of Xe gas bubbles. Since the precipitation will change the defect morphology and reduce the sizes of each isolated defects, so to intensify the quantum size effects of nano-particles and induce the observed band gap broadening. At the same time, the increase of the defects densities and the change of the defects morphology will rise the high probability of non-radiation excitation and lead to the vanishing of the photo-luminescence.4) The undoped Ni+-implantation A12O3 has a broad band centered at 400nm, which is attributed to Ni2+: 3A2→3T1(F) transition. For the other three doped crystals, no newabsorption band had appeared because the transitions of Ni2+ and Cr3+ ions are nearly in the same wavelength range. The effect of Ni+ion on luminescence had not been detected by fluorescence experiments for implanted doped crystals.5) The Xe ion peak concentration lies at a depth of about 47nm under the surface. After ion implantations, the two peaks in O1S spectrum merge into a single one. This indicates that the chemical surroundings of the two types of oxygen sites become similar after the irradiation. The implanted Ni+ions are mainly in charged state of Ni?(metallic). After annealing in air the changed state turns to Ni2+.6) The peak damage ~350dpa occurs at a depth of about 30ntn in 1 × 1017 cm-2 Xe+-implanted YSZ, but the SAD (selected area diffiaction) patterns indicated no amorphization. However, the peak damage ~320dpa occurs at a depth of about 20nm in 1 × 1017 cm-2Ni+-implanted Al2O3, which leads to amorphization.