Decay of electronic excitations into radiation defects in ionic crystals

On the Way to Optoionics

“…[13,14,23] As the momentum and energy transferred to a crystal by X-rays are clearly insufficient to cause a knockout of ions from regular position to interstices, a more intricate defect formation mechanism should exist. Lushchik et al [17] were the first to show for the wide bandgap NaCl that vacuum ultraviolet light produces excitons (a concept already suggested by Frenkel) and electron-hole pairs, which then results in the same radiation damage as under X-ray (or even γ-ray) irradiation. This has led to the fundamental conclusion that Frenkel pairs can be created as a result of non-radiative annihilation of selftrapped excitons (self-trapped hole X 2 À recombines with trapped electron in the excited state).…”

“…Thus, it is momentum and energy transfer connected with these particles/ electrons that result in the formation of spatially correlated pairs of vacancies and interstitials. [14,17,18] For wide band gap ionic crystals (for example, KCI, KBr), there exists another possibility of point defect generation, namely through electronic excitation using photons (excitonic mechanism). [17,19,20] It was already shown very early [21] that alkali halides (AH) can be colored by X-rays whose energies exceed the band gap.…”

“…[14,17,18] For wide band gap ionic crystals (for example, KCI, KBr), there exists another possibility of point defect generation, namely through electronic excitation using photons (excitonic mechanism). [17,19,20] It was already shown very early [21] that alkali halides (AH) can be colored by X-rays whose energies exceed the band gap. This color arises due to the formation of F centers (from the German Farbzentrum, or color center), that is, anion vacancies having captured an excess electron, which is then able to absorb light in the visible spectrum.…”

Hydrogen photosensitization, photochromism, and surface-enhanced infrared absorption in AgI thin films

“…On the other hand, microscopically, the photoinjection of electrons and protons into AgI may be considered as injection of movable defects, which, in turn, facilitates formation of point defects under illumination via collapse of electron excitation in the vicinity of injected impurity atoms. 50,51 The injection of hydrogen atoms facilitates also the agglomeration of silver atoms; the protons, being localized in the vicinity of I − anions, weaken the Ag-I bonds. There are two types of excitation of the halide surface: short-lifetime excitation by light and indefinitely longlifetime "excitation" by the hydrogen atoms ͑the electrons and the protons͒, with both the point defect formation and the agglomeration of silver atoms being facilitated.…”

Effect of Magnetic Field on the Decay Kinetics and Polarization of the AT Emission of KCl:Ga at 0.38 K

“…Therefore, a n investigation of gallium-doped crystals i s of particular interest in view of the luminescence centre model [l, 21 which suggests a strong interaction of impurity optical electrons with non-totally symmetric vibrations of the crystal lattice and considers s pin-orbit interaction as a small perturbation. For the first time alkali halides doped with galliuni were synthesized and investigated in [3]. Two emission bands -A, and A,are observed on excitation in the A absorption band of Ga+ centres.…”