Electronic excitations and defect creation in wide-gap MgO and Lu3Al5O12 crystals irradiated with swift heavy ions

Abstract

A comparative study of radiation effects in two groups of single crystals with an energy gap of about 8 eV possessing drastically different lattice and electron energy structures − fcc MgO and Lu 3 Al 5 O 12 with 160 atoms per a unit cell − has been performed using crystal irradiation with vacuum ultraviolet radiation, electrons, fast fission neutrons and, in particular, ~2.2 GeV uranium ions. In MgO with the absence of self-trapping for valence holes, the localization of holes near impurity ions or bivacancies (both as-grown or induced by a plastic stress) has been detected. In LuAG, the peculiarities of the motion of hole polarons and excitons, the radius of which is smaller than the size of a unit cell, have been revealed and analysed. The irradiation of MgO and LuAG with swift heavy ions providing an extremely high density of electronic excitations causes also the nonimpact creation of long-lived Frenkel defects in an oxygen sublattice.

Influence of complex impurity centres on radiation damage in wide-gap metal oxides

“…[39], the ratio of these reflection spectra (irradiated/virgin) contains a pronounced peak at ~7.1 eV and a small peculiarity at ~8.0 eV, that, in our opinion, confirm the formation of single and more complex (pair) LuAl defects. Our recent measurements have shown that the thermal annealing of the ~7 eV-band of SHI-induced optical absorption efficiently occurs above 1100 K (at about a half of the melting point), where the intensive ionic movement takes place already.…”

“…In SHI-irradiated LuAG, the enhancement of the emission peak amplitude was detected only at 3.254.25 eV. The absolute enhancement of this emission at ~3.75 eV of unknown origin was detected due to its short decay time (~70 ns) at 80 K [39].…”

“…[39]. Besides Ce 3+ luminescence (~2.4 eV, CeLu), the emissions related to self-trapped excitons (~5.1 eV) and LuAl (~4.5 eV) were distinguished in the spectrum for a virgin LuAG.…”

“…Even these isovalent to Mg 2+ impurity ions serve as efficient traps for radiation-induced holes and, therefore, increase the probability of a sequent recombination of hot conduction electrons with trapped-hole centres (hot eh recombination) resulting in the creation of FDs (see [38,39] and references therein). that is needed for the pronounced "luminescent protection", the situation becomes more complicated due to the formation of pair impurity centres (see also Section 5).…”

“…The creation of F and F + centres (two or one electrons trapped by an oxygen vacancy) was detected at periphery of cylindrical tracks of SHIs in LuAG single crystals using highly sensitive luminescent methods [34,39]. It has also been suggested than the collapse of mobile discrete breathers in certain lattice places causes the creation of complex defects involving many host atoms [34].…”