Defect creation caused by the decay of cation excitons and hot electron–hole recombination in wide-gap dielectrics

Abstract

Insufficient radiation resistance of construction materials is the Achilles heel for thermonuclear energetics. In wide-gap dielectrics, Frenkel defects are created not only because of the knock-out (impact) mechanism but also because of the decay of the electronic excitations formed during the irradiation (i.e. due to nonimpact mechanisms). The processes of the defect creation at the irradiation of highly pure LiF single crystals at 6-8 K by 1-30-keV electrons, X-rays, or synchrotron radiation of 12-70 eV have been investigated. The annealing processes of these defects in a temperature range up to 200 K have been studied as well. In LiF, creation has been revealed for the following: (1) F-H pairs caused by the decay of anion excitons or by the recombination of electrons and holes, (2) F 0 -H-V K and F-I-V K defect groups at the decay of cation excitons (62 eV), or (3) 20-keV electron irradiation. The mechanism of defect creation at the recombination of hot holes and hot electrons has been discussed for a-SiO 2 crystals with an energy gap between the subbands of a valence band. One of the possible ways to suppress this mechanism (''luminescent defence'') is doping a material by luminescent impurities able to capture a part of the energy of hot carriers before their relaxation and recombination (e.g. in MgO:Cr).

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

“…The efficient creation of stable FDs at the decay of cation excitons (hν ~ 62 eV) has been also detected in LiF crystals [7]. By generalizing the results for some metal halides, we initiated the investigation of the role of hot recombination in the FD creation in metal oxides as well [8].…”

Low-temperature creation of Frenkel defects via hot electron-hole recombination in highly pure NaCl single crystals

“…So, the FranckHertz effect was considered as some kind of "luminescent protection" against the radiation damage induced by hot e-h recombination. 12,14,15,36,37 However, several limitations do not allow to use this approach for significant increase of material radiation resistance. 15 In NaCl at room temperature, the value of E FD is close to E g .…”

Franck–Hertz effect in cathodo- and photoluminescence of wide-gap materials

“…The separation of FHE from the fast excitonic and e-h mechanisms of photon multiplication in binary and complex metal oxides runs into obvious problems due to a sharp rise of E v up to the value of E g in these WGM. For instance, the value of E v z 6.6 eV can be experimentally estimated from the spectra of fast intraband luminescence measured under excitation of MgO crystals by nanosecond single 300 eV electron pulses (Lushchik et al, 2006).…”

“…In such materials, the separation of FHE in low-temperature photo-and cathodoluminescence (PL and CL, respectively) is of obvious interest for both fundamental studies and various technical applications, such as the elaboration of novel spectral transformers for neon luminescent tubes and xenon plasma display panels or the increase of WGM radiation resistance by weakening hot electronhole (e-h) recombination with the creation of Frenkel defects (Lushchik et al, 2006).…”

“…The elementary mechanisms of photon multiplication have been studied in binary and complex metal oxides as well (Lushchik et al, 2005(Lushchik et al, , 2006. The separation and elucidation of the third multiplication mechanism in WGM -the solid-state analogue of FHE appeared to be much more complicated (Lushchik et al, 1966(Lushchik et al, , 1998(Lushchik et al, , 2005Feldbach et al, 1997;Kirm et al, 1997;Makhov et al, 2008).…”