Photo luminescence studies of gamma-irradiated CaF2 : Dy : Pb : Na single crystals

摘要

The optical absorption (OA) and photoluminescence (hereafter referred to as luminescence) studies were made on CaF2:Dy:Pb:Na single crystals (Dy-0.005 at, Pb-O. 188 at and Na-0.007 at) before and after gamma-irradiation. The unirradiated crystal exhibited a strong OA band around 6.36 eV attributed to the 'A' band absorption of Pb2+ ions. The gamma-irradiated crystal exhibited OA bands around 2.06, 3.28, 3.75 (broad shoulder) and 2.48 eV. The first three bands could be tentatively attributed to M-Na centre when compared with that of the coloured CaF2:Na. The origin of 2.48 eV band was not explicitly known. Luminescence emission and excitation of Pb2+ and Dy3+ ions were negligible in the unirradiated crystal. Irradiated crystal exhibited a strong excitation spectrum with overlapping bands, due to different colour centres, in the UV-vis region for the 2.15 eV emission characteristic of Dy3+ ion. When excited, the absorbed energy (may be a part) was transferred from a colour centre to nearby Dy 31 ions and DY3+ characteristic emission was observed. Exciting the irradiated crystal around 3.28 eV yielded emission at 2.56, 2.15 and 1.76 eV. The first two emission bands were due to Dy3+ ions. The excitation spectrum for the 1.76 eV emission showed two prominent bands around 2.02 and 3.08 eV and hence the emission was attributed to the M-Na centre. The luminescence mechanism was described. (c) 2007 Elsevier B.V. All rights reserved.