Radiation-produced electron and hole centres in oxygen-containing BaFBr. I. EPR and ODEPR studies

Abstract

An 0centre formed upon hole trapping by 0'in X-irradiated BaFBr is long-lived at room temperature and has been detected by EPR below 30 K. It can also be produced in low wncentrations by expos-of BaFBr to subbandgap (200400 nm) radiation. The formation of F(Br-) centres at chargecompensating bromide ion vacancies is a corollary of the photoionivltion of Oz-. High eoneentrations of oxide have been successfully introduced into this material by doping with anhydrous BaO. including Ba"O for unambiguous identification of the 0defect.Oxide addition and the formation of 0-produces a series of optical bands that have been assigned using a wmbination of optical and magneboptical techniques. The inBwnce of the material preparation conditions on the concentration of 0'is dircussed and possible mechanisms for the formation of 0are proposed

New synthesis of high-quality storage phosphors

“…Both the formation of BaO through the decomposition of BaCO 3 and the formation of oxygen through the CO 2 reduction are hold responsible for oxygen incorporation into the BaFBr:Eu 2þ lattice and the generation of bromine based anion vacancies (F þ (Br)-centers). EPR confirms this line of thinking and has shown that O 2À can occupy different halide sites in BaFBr:Eu 2þ but favorably replaces fluoride ions thereby acting as charge compensation centers for F þ (Br)-centers as anion vacancies (Eachus et al, 1991). Most likely the excess of fluoride ions following from Eq.…”

Electron traps in Ca2+- or Sr2+-doped BaFBr:Eu2+ x-ray storage phosphors

“…After the exciton decay the electron is trapped at that vacancy and the V K center formed migrates away at room temperature and may transfer its hole to another defect ͑note, V K centers are not stable at room temperature 9,15-17 ͒. For example, it reacts with O F 2Ϫ to form O F Ϫ , 15,16 but there may also be another, unknown, hole center ͑see the discussion in Ref. 3-5͒. It seems that for the preferential generation of F͑Br Ϫ ͒ and F A ͑Br Ϫ ͒ centers the origin of the Br Ϫ vacancies is not important.…”

Storage Phosphors for Medical Imaging

“…The lack of experimental support for the described models gave rise to a third proposal for the formation of defect centers by Spaeth et al [16,17,18,19,20]. This model equally assumes that vacancies are already present in the virgin lattice.…”