Journal of Physical Chemistry B, Vol.109, No.23, 11505-11511, 2005
X-ray storage luminescence of BaFCl : Eu2+ single crystals
Temperature behaviors of X-ray luminescence (XL), photoluminescence (PL), photostitnulated luminescence, and thermoluminescence (TL) were studied in BaFCl:Eu2+ single crystals from room temperature to liquid nitrogen temperature. Six emissions at 275, 315, 365, 385, 435, and 500 nm were observed in the XL spectra and are attributed to Cl excitons, Vk(Cl-2(-)), the 4f(6)5d(1) -> ((2)e(g)) -> 4f(7) (S-8(7/2)) transition of Eu2+, and oxygen vacancies, respectively. Three emission peaks at 315, 365, and 390 rim were observed in the PL and TL measurements. These three emissions are from the transitions of 4f(7)(6I(7/2)) -> 4f(7)(S-8(7/2)) -> 4f(7)(P-6(7/2)) -> 4f(7)(S-8(7/2)), and 4f(6)5d(1) ((2)e(g)) -> 4(f)(S-8(7/2)) of Eu2+, respectively. In our measurements, we observed that the emission of Eu2+ increases in intensity upon beta-irradiation and did not see any signals related to Eu3+ ions, which indicates that Eu2+ ions might not be oxidized to Eu3+ upon X-ray or beta-irradiation. Instead, the color centers, Cl excitons, and oxygen defects are created and are stable at room temperature, and they might play a key role in the storage luminescence.