Kurtsev D. Obtaining of efficient scintillators based on Lu2xGd2-2xSiO5: Ce (LGSO: Ce) crystals

LGSO:Ce crystals with improved properties were obtained in the present work with the scintillation yield of 29000 phot./MeV, the energy resolution of 6.7% at 662 keV, the afterglow level of 0.025-0.1% after 5 ms, and 50 ns time of the main component of scintillation decay. The optimal combination of scintillation characteristics is observed within the x = 0.4-0.6 range. The concentration of cerium should not exceed 0.8 at.% to prevent the reabsorbtion of luminescence in the crystal and the Сe3+ occurrence in СeO6 polyhedra. A patent for the method of single crystals obtaining was issued. Structural properties of LGSO:Ce crystals were studied. At x ? 0.1 the crystals belong to the P21/с monoclinic structure, at x ? 0.2 crystals belong to the C2/c monoclinic structure. In the 0.1 < x < 0.2 range the crystals can be crystallized into one of these structures depending on the growth conditions. The trivalent cations distribution in the crystallographic positions was studied. It was determined that the large Gd3+ and Ce3+ ions occupy preferably 9-fold oxygen-coordinated sites in crystals with the P21/c structure and 7-fold oxygen-coordinated sites in the C2/c crystal structure. The method was developed to minimize the concentration of the activator in 6-fold positions in the C2/c structure, providing the increase in light yield. The procedure of post-growth annealing of LGSO:Ce crystals in oxidizing atmosphere was developed providing a reduction of oxygen vacancies concentration and improvement of energy resolution at 662 keV by 0.5-2.5%. Finally, the method for obtaining large-size LGSO:Ce crystals with diameter up to 35 mm and length up to 150 mm was developed. The feasibility of LGSO:Ce application in high energy physics experiments and medical imaging was shown.