Defect formation and VUV luminescence in BaF 2

Abstract

Nominally pure BaF 2 single crystals were investigated at 77 K with optical absorption and electron paramagnetic resonance to understand the mechanism of radiation damage. We find that X-irradiation at 77 K of undoped BaF 2 produces V k -and F-centres having absorption bands at 3.4 and 2.3 eV respectively.

The Lu-doping effect on the emission and the coloration of pure and Ce-doped crystals

“…Contrary to these samples, BaF 2 : Lu and BaF 2 : Ce, Lu crystals become slightly colored at doses higher than 10 2 Gy due to induced weak absorption bands ( K 1.6 cm −1 ) with maxima at 544 and 637 nm. Similar peaks were revealed earlier in BaF 2 doped with La ions (Nepomnyashchikh et al, 2002). Therefore, the observed absorption is associated with intrinsic defects rather than RE impurity.…”

“…ions have filled outer shells and have no absorption bands in the energy gap of BaF 2 (E g = 12 eV). La-doped BaF 2 crystals and Ba x−1 Lu x F 2+x solid solutions have been the subject of many studies (see Nepomnyashchikh et al, 2002;Radzhabov, 2002). The La addition into BaF 2 leads to the suppression of the slow component and to the loss of the radiation resistance, which is a drawback for scintillation usage.…”

First-principles simulations on the aggregation of F centers in BaF2: R centers

“…For the F0-midway case, the trapped electron (the F center) is localized (−0.429 e) on both sides of F0 equally and the effective charge of F0 is − 0.793 e, being much smaller than the fluorine charge of − 0.923 e in a perfect BaF 2 crystal. BaF 2 containing F centers exhibits optical absorption centered around 2.3 eV experimentally [30]. Our result for defect levels suggests a possible mechanism for this optical absorption.…”

“…More precise values for the peak position of the F band and values for the spin-orbit coupling constant in the excited 2 P state of the F band were obtained, using magneto-optical methods, by Cavenett et al [29]. Nepomnyashchikh et al measured that X-ray irradiation at 77 K of undoped BaF 2 produces F centers having an absorption band at 2.3 eV [30]. F centers in alkaline-earth fluoride also have been studied theoretically with the Xα method [31,32], and Puchina et al, using the Hartree-Fock (HF) embedded molecular cluster method, performed calculations for the ground electronic state of the F center and its optical absorption energy [15].…”

Photostimulated detection of defect formation in BaF2 under irradiation of synchrotron radiation

“…Lushchik et al have studied the effect of vacuum ultraviolet (VUV) radiation on defect formation in a wide energy range with the use of synchrotron radiation (SR) and clarified the excitonic and electron‐hole mechanisms 4. On the other hand, although even in recent years many experimental and theoretical works have been performed on the lattice defects in BaF 2 5–7, few works have investigated the effects of VUV irradiation on the defect formation 8 and thus the detailed creation mechanisms of lattice defects under photoexcitation have not been well understood. We think that among alkaline‐earth fluorides, the study on BaF 2 is of special interest from both the points of view of applied and basic research.…”