Li2B4O7 crystals doped with Eu and Cu: electrophysical properties and structure

LTB:Cu and LTB:Eu crystals are characterized by intense photoluminescence in the region of 370 and 580-700nm, respectively. Copper is present in the crystal in the univalent state, europium is trivalent. Photoluminescence in LTB:Eu is caused by transitions in EU ³+ ions in weak electric fields. In doped LTB samples a complex defect is observed. It seems to consist of the recombination center of the dopant ion interacting with a structure defect located in its neighbourhood. The excitation of all the samples is accompanied with light sum accumulation by means of the defects formed in the process of excitation. In the region of 290-600K, three types of defects with E=0.84, 0.95 and l.leV are observed in undoped LTB crystal. Doping with europium leads to the disappearance of a new type of defects with E=0.84eV and to the increase of the quantity of all other defects. Doping with copper results in the appearance of a new type of defects (E=1.18eV) bound up with Cu⁺ ions. The formation of the new defect reduces the probability of radiative recombination of defects with E=0.95eV and E=l.leV. The increase of irradiation dose makes the quantity of all types of defects slightly larger