Elektronenspin-Resonanz und Photochemie des U2-Zentrums in Alkalihalogenid-Kristallen
The photochemical reactions involved in the production and in the bleaching of U2 centers (interstitial hydrogen atoms) in KCl, KBr and NaCl crystals are investigated by measuring the optical absorption spectra of the crystals at low temperatures. The U2 centers are prepared by UV irradiation of hydroxide- and hydride-doped crystals. The electron spin resonance of KCl, KBr and NaCl crystals with U2 centers at low temperatures reveals a well-resolved hyperfine splitting due to interactions of the hydrogen atom with four neighbouring halogen ions. The U2 center can be described as a tetrahedal [HX4]4−-molecule ion, in which one hole, bound mainly at the hydrogen atom and partially at the surrounding halogen ions, gives rise to the spin resonance.