[en] The thermoluminescent properties of transparent and colorless plates (6x6x1mm) of undoped and Cu-doped lithium tetraborate single crystals produced in the Institute of Electron Physics (Ukraine) were investigated using low and high LET radiations and mixed-radiation fields (photon and thermal neutrons). A comparative characterization of undoped (LTB) and Cu-doped (LTB:Cu) lithium tetraborate single crystals to TLD-100, TLD-700, TLD-700H and Al₂O₃:Mg,Y (D-3) dosemeters is also reported. The results show that LTB:Cu is approximately 50 times more sensitive to gamma radiation than LTB and 5 times more sensitive as compared with TLD-100 dosemeters. On the other hand, LTB:Cu is about 5 times less sensitive to thermal neutrons than LTB, which suggests the application of paired LTB and LTB:Cu for mixed-field dosimetry. Both LTB and LTB:Cu single crystals have negligible light sensitivities, which is a major improvement over former lithium tetraborate-based TLDs