Study of the defects in La3Ta0.5Ga5.5O14 single crystals

Defects that are formed during crystal growth pose a serious obstacle for potential application of La3Ga5.5Ta0.5O14 (LGT) as a laser or piezoelectric crystal. We have performed the study of the defects origin in LGT crystals grown in different atmospheres using optical, EPR and time-resolved luminescence characterization methods. The absorption bands detected in the transparency region at 290, 360 and 490 nm (T=300 K) demonstrate different dependence on crystal annealing in vacuum and air. EPR analysis demonstrated that the defects responsible for these bands are non-paramagnetic. X-ray irradiation results in hole trapping by oxygen ions thus forming O− centers perturbed by neighboring defects. New arguments in favor of the existence of TaGa(2) antisite defects in LGT are presented. The absorption bands at 255 and 290 nm are related to oxygen vacancies localized at the different sites of crystal lattice. The absorption band at 360 nm is related to cation vacancies (VGa3−orVLa3−). Time-resolved luminescence spectroscopy allowed to identify excitation processes responsible for the defect-related emission bands.