Creation of groups of spatially correlated excitations in wide‐gap solids

Abstract

Abstract Processes of efficient creation of groups of electronic excitations (EEs) or defects have been considered for radiation‐sensitive (alkali halides) and radiation‐resistant (metal oxides) single crystals. In MgO, pure or doped with Be 2+ , Ca 2+ and Al 3+ ions, the 7.63 eV edge emission of anion excitons is efficiently excited at 10 K in a wide region of 30–90 eV. Multiplication process with the creation of secondary electron–hole pairs and the decay process of cation excitations are compared in crystals of two types: (i) KCl, KBr and LiF, where anion excitons and valence holes undergo self‐trapping and (ii) a MgO crystal, where no self‐trapping of excitations occurs. In alkali halides, a group of spatially correlated EEs, formed at photon absorption, is transformed into an F–I–V K triplet of defects at 5 K or into a temperature‐stable F centre and a trihalide molecule (e.g., Br 3 – ) at 295 K. In BaMgAl 10 O 17 :Eu at 295 K, the 2.72 eV emission of Eu 2+ centres with quantum yield of 1.1–3.5 at the excitation by photons of 13–30 eV has been obtained. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)