Luminescence and hole center formation by VUV-radiation in MgO : Al and MgO : Ge crystals

The creation spectra of V-AI and V- hole centers have been measured for MgO :Al and MgO:OH crystals using photons 6-10 eV.V-Al centers are formed (i) d ue to the hole trapping by "a cation vacancy + an Al3+ ion" associations (r egion of interband transitions, h nu > 7.85 eV), (ii) due to the photoioniz ation of oxygen ions near associations (7.35-7.65 eV) or (iii) at the inter action of excitons with associations (7.7-7.8 eV). For the first time a MgO single crystal was doped with Ge2+ 'mercury-like' ions. The emission of Ge 2+ centers (similar to 3 eV) can be efficiently excited at 4s(2)-->4s4p ele ctron transitions in Ge2+ ions (4.8-6.4 eV) as well as at the formation of electron-hole pairs by 8-36 eV-photons. The absorption of one photon of 25 or 30 eV leads to the creation of two or three electron-hole pairs, respect ively.