Structure and optical properties of two types of F centre in BaFBr

Abstract

A detailed investigation of the optical absorption and emission bands from the two types of F centre in BaFBr is reported, using optical, magneto-optical, and optically detected electron paramagnetic resonance and electron nuclear double resonance (ENDOR) techniques. With conventional ENDOR, the superhyperfine interactions of the F(Br-) centre are investigated in detail. It was found from the luminescence experiments that the two types of F centre are spatially correlated when they are created by X-irradiation in qualitative agreement with the observation of cross relaxation effects, as reported elsewhere.

Physics and Current Understanding of X-Ray Storage Phosphors

“…The absorption peak of F(Br --) centres is at 580 nm for the electrical light vector perpendicular to the crystal c-axis, while it is at 510 nm for E k c. For F(F --) centres the absorption peaks are at 470 nm for E ? c and at 520 nm for E k c [36]. It is seen qualitatively in Fig.…”

“…EPR spectrum detected in the MCDA band of the V K ðBr À 2 Þ centre in BaFBr after X-irradiation at 4.2 K, recorded for B k c at T = 1.5 K applying a microwave frequency of 24 GHz. The spectrum shows cross-relaxations to the F(Br --) centre and to Eu 2+ [49] needed for the read-out process is higher for oxygen-poor BaFBr. Thus, it seems that oxygen is involved in two ways in the PSL mechanism: It provides vacancies for the F(Br --) generation and it somehow seems to influence favourably the photostimulation of the triple aggregate centres in that less stimulation energy is needed for read-out and a high PSL intensity results after short stimulation.…”

“…Direct evidence for a spatial correlation between F centres, O À F centres and Eu 2+ was given with cross-relaxation spectroscopy using magneto-optical techniques (Fig. 15) [49].…”

“…When Xirradiating at low temperature, V K centres also show this correlation with the other 17 O-doped BaFBr after X-irradiation at RT, recorded for B k c at T = 5 K applying a microwave frequency of 9.42 GHz. The bars indicate the 17 O hyperfine splittings [39] centres [43,49]. This leads to the speculation that an exciton decay occurs at the Eu 2+ activator forming electron and hole trap centres and that there is a spatial correlation between the O 2À F -anion vacancy pairs and the Eu 2+ activators generated during the production of the material (Fig.…”

Photostimulated luminescence of Ba12F19Cl5:Eu

“…2 are intimately related to the stored image after UV irradiation. Their positions and shapes are reminiscent of the F bands in the matlockites BaFX, X=Cl,Br and in BaF 2 as can be seen in Table 1 where published results of the FðXÞ and FðFÞ centers in these hosts [14,15] are given, together with the presently reported ones. But, they cannot globally be assigned to F centers in spite of the fact that the optical absorption bands of the intrinsic exciton (at 69,500 and 70,400 cm À1 in BaFCl [16]) and (in part) of the V K or H centers (e.g.…”