Optical Absorption, Fluorescence, and Thermally Stimulated Emission on CaF<inf>2</inf> : Dy: Pb Single Crystals

The optical absorption (OA) spectra of unirradiated crystals of CaF2 doped with 0.1% Dy (by mol%) and 0.1% Pb, hereafter called crystal I, and doped with 0.2% Dy and 0.1% Pb, called crystal II, indicate the presence of a small amount of dysprosium in their divalent state (Dy2+). There is an increasing absorption towards 6.5 eV. On y‐irradiation the concentration of Dy2+ ions is found to increase. Fluorescence of these crystals shows characteristic Dy3+ emission at 1.62, 1.85, 2.16, and 2.85 eV (4F9/2→6H9/2), 6H11/2, 6H13/2, 6H15/2. In thermoluminescence (TL) glow after γ‐irradiation at room temperature crystal I shows six peaks in the temperature range (300 to 700 K) studied. Dy3+ is found to be the major luminescent centre under all these glow peaks. In addition to the Dy3+ emission bands there are two bands in the UV region at 4.94 and 5.93 eV in TL emission. For higher concentrations of lead the results are somewhat different. Crystal III (with 0.01% Dy and 0.5% Pb) and crystal IV (with 0.02% Dy and 0.5% Pb) show a strong absorption band around 6.4 eV. On irradiation prominent absorption bands are observed around 2.04 and 3.21 eV. These are attributed to an F centre associated with the rare‐earth ion in its divalent state (Dy2+ –F centre complex), akin to the FA centre in alkali halides. It is also found that the lead ions (Pb2+) when excited, transfer their energy to nearby Dy3+ ions, leading to the characteristic emission of Dy3+ ions. Copyright © 1993 WILEY‐VCH Verlag GmbH & Co. KGaA