Irradiation effects on Ce3+thermoluminescence centres of mineral Caf2

Abstract

Abstract Trivalent rare-earth trace impurities are the emitters of thermoluminescence (TL) in the fluorite mineral. In this paper the cerium associated part of the TL spectrum is explained as originating from three types of Ce3+ centres: (1) compensated locally by substitutional O2− impurity in the adjacent lattice position, (2) associated with interstitial F− in the tetragonal or trigonal symmetry, (3) unassociated with other impurities. At smaller radiation doses (< 100 Gy) the emission is predominantly from O2− compensated Ce3+ centres. The spectrum at high doses (≳100 Gy) originates from Ce3+ centres without O2− compensators in the immediate vicinity. It is hypothesized that at low doses an electron is captured in the Ce3+ -O2− impurity centre leading to the conversion of Ce3+ to Ce2+. At high doses, a hole also is captured, with the result that this Ce3+-O2− centre then gets converted to Ce2+-O−. This changed configuration is stable up to 500°C. As a result of this, at high doses the glow peaks appearing below 300°C produce emission mainly from Ce3+ centres without O2− compensators, whereas at lower doses the spectra are of O2− compensated centres. The glow peaks of 75 and 150°C are attributed to perturbed Vk centres and that of 500°C is attributed to Ce3+-O2− centre in which electron-hole exchange may take place locally.