X-ray-Excited Radioluminescence, Thermoluminescence, and Tunnel Recombination Processes of Sc3+ Centers in LuAG:Sc Crystal Scintillators

Single crystals of Lu3Al5O12 (LuAG) doped with 1 at. % Sc3+ were investigated to clarify the role of Sc3+ centers in radioluminescence (RL), thermoluminescence (TSL), and tunnel luminescence (TL) processes. LuAG:Sc (1%) crystals were grown by the Horizontal Direct Crystallization method in a reducing CO/CO2 atmosphere and compared with an undoped LuAG counterpart prepared under the same conditions. X-ray-excited RL spectra were measured in the temperature range of 80–400 K. Trap-related phenomena were studied by TSL spectroscopy and glow-curve analysis after X-ray irradiation at 80 K, as well as by measurements of TL following X-ray switch-off at 80 K. Sc3+ doping introduces intense UV emission associated with Sc3+ centers occupying dodecahedral (ScLu) and octahedral (ScAl) sites, while their interaction with LuAl antisite defects and oxygen vacancies VO modifies the radiative and trapping processes. LuAl antisite defects and their associations with oxygen vacancies, as well as Sc3+ dopants, also lead to the formation of efficient trapping centers responsible for pronounced TSL and TL signals in both LuAG and LuAG:Sc (1%) crystals. Correlation of the XRL, TSL, and TL spectra indicates that Sc3+ centers participate in both prompt and delayed recombination, while the different spectral contributions indicate the involvement of distinct or partially overlapping trapping and recombination pathways. The obtained results provide insight into charge-trapping and recombination processes in LuAG-based crystal scintillators doped with isoelectronic impurities.