Concentration and temperature dependence of luminescence for the copper-doped lithium tetraborate single crystals

The copper-doped lithium tetraborate (Li2B4O7:Cu) is one of the famous tissue-equivalent materials for the thermoluminescent dosimetry, being characterized by a high radiation resistivity, a linear dose dependence, a wide operation dose range and a weak dependence of the dose on the ionizing radiation energy. We have performed the thermostimulated luminescence (TSL) studies of the lithium tetraborate single crystals doped with various amount of copper. There was found the optimal dopant concentration (19.1 x 10(-3) wt. % Cu) at which the maximum TSL intensity of the high-temperature maximum occurs. Further increase of copper concentration results in the decrease of the TSL intensity due to the concentrational damping of luminescence. For the Li2B4O7 Single crystals with optimal Cu dopant concentration within the temperature range under study TSL is primarily due to the carriers released from two local trapping levels with E-t1 = 0.90 +/- 0.03 eV, E-t2 = 1.72 +/- 0.07 eV energies and frequency factors of 4 x 10(10) s(-1) and 5 x 10(16) s(-1), respectively. The occurrence of these local levels has a considerable influence on the temperature dependence of X-ray luminescence. Above 215 degrees C the temperature damping of luminescence is observed This damping is well described by the Mott's formula with the activation energy E-A = 0.65 +/- 0.05 eV.