Cathodo-luminescence of color centers induced in sapphire and yttria-stabilized zirconia by high-energy electrons

Abstract

We have studied the color-center production in sapphire and yttria-stabilized zirconia (YSZ) single crystals by cathodo-luminescence (CL) spectroscopy for electron energies ranging between 400 and 1250 keV in a high-voltage electron microscope. Emission spectra were collected for in-beam conditions near room temperature and at 200 K. Comparison was made with CL spectra recorded for 3-keV–20-keV electrons in a scanning electron microscope. For high-energy electrons, CL spectra for sapphire revealed broad emission bands centered at photon energies about 3.0 eV and 3.8 eV that were, respectively, assigned to oxygen vacancies (F0 and F+ centers) induced by elastic collisions, on the basis of photoluminescence (PL) data. No such bands were recorded for 3-keV and 5-keV electrons. Two similar bands were also recorded for YSZ (with 9.5 and 18 mol. % yttria) at about 2.8 eV and 4.1 eV that can be, respectively, attributed to the native oxygen vacancies (F2+ centers) and F+ centers. The 4.1-eV band was not seen for 20-keV electrons: it was only produced for high electron energies by elastic collision processes. Instead, the small side band was also found at 2.85 eV for 20-keV electrons. PL excitation contour plots of virgin and irradiated YSZ were also recorded to support our discussion on point-defect identification. CL band intensities show a maximum versus electron energy, whereas point-defect concentrations should increase due to the increase of oxygen atom displacement cross section. The effect of electron energy on the different steps of the CL process is discussed to account for such a behavior.

Atomic, electronic and magnetic structure of an oxygen interstitial in neutron-irradiated Al2O3 single crystals

“…Radiation damage of α-Al 2 O 3 caused by fast neutrons, energetic electrons and ions have been investigated for many years 1,2,9,[12][13][14][15][16][17][18][19][20][21][22][23] . The optical characteristics of the anion-vacancy-related elementary Frenkel defects-F + and F centers (one or two electrons trapped by an oxygen vacancy) have been thoroughly studied in irradiated and additively colored Al 2 O 3 crystals [13][14][15][16] .…”

Thermal annealing and transformation of dimer F centers in neutron-irradiated Al2O3 single crystals

“…below the beginning of the recharging processes of the F 2 centers, were detected. On the other hand, only episodic studies of TSL have been performed in pure α-Al 2 O 3 exposed to particle irradiation (neutrons, energetic ions and electrons) [16,39,40] . In particular, irradiation with mainly thermal neutrons [39] or fast neutrons at 20 K [39] leads to the appearance of TSL peaks significantly below the high-temperature one detected after crystal irradiation by fast fis-sion neutrons in the present study (see Fig.…”

“…Note that ~700 K was a technical limit for a TSL setup used in Ref. 16 for the measurements for heavyion-irradiated corundum crystals. In our opinion, the TSL above 700 K detected in the present study can be related to the transformation processes with the F 2 -type centers according to the above-suggested scenario.…”

“…The processes of radiation damage under irradiation of α-Al 2 O 3 crystals by fast fission neutrons, energetic electrons and swift heavy ions have been investigated for many years [ 1,[6][7][8][9][10][11][12][13][14][15][16][17]. In general, tolerance of a functional material to intentional irradiation is mainly determined by the accumulation of primary lattice point defects − vacancy-interstitial Frenkel pairs.…”

Evidence for the formation of two types of oxygen interstitials in neutron-irradiated α-Al2O3 single crystals

“…Experimental studies of radiation processes caused by α-Al 2 O 3 exposure to radiation of different types − fast fission neutrons, energetic electrons or heavy ions—have been performed for many years 21 – 36 . The optical characteristics (optical absorption and emission bands) of the main point lattice defects—the so-called F + and F centers, which represent an oxygen vacancy with one or two captured electrons, respectively, have been thoroughly studied in irradiated and additively colored (thermochemically reduced) corundum crystals 24 – 28 , 37 .…”