ИСТИНА

The irradiation response of La3Ga5,5Ta0,5O14 (LGT) and Ca3TaGa3Si2O14 (CTGS)crystals is poorly investigated and necessary for the study of their defect structure. Study of defects structure and its formation in multicomponent oxide single-crystal dielectric materials is the nontrivial task. The anisotropy of complicated structures with non-cubic lattice leads to various phenomena, e.g. dichroism. Absorption spectra in near UV and visible regions are sensitive to the point defects and their associations in crystal structure. Each absorption band on the spectra is associated with specific type or group of point defects. For LGT and CTGS three absorption bands are observed at λ ~290 nm, at λ ~360 nm and λ ~(460-480). According to [1] the absorption band at λ ~(460- 480) nm is identified with oxygen defects and F-centers (Vo++ , 2e- ). The origin of two other bands is still not clear. The study of the irradiation effects on ion structures is a productive method for investigation of the origin of the defect structure and mechanisms of its formation. Here, we present the results of our study of LGT and CTGS optical properties under electron and proton irradiations. All investigated samples were cut from crystals grown in JSC "Fomos-Materials" Co. using Czochralski method in iridium crucibles. Electron irradiation was performed at the Center of Physical Measurements Investigations of IPCE RAS using the linear accelerator (energy 6 MeV, flux 4·1012 cm–2 ·s–1 , fluences up to 1,2∙1016 cm-2 ). Proton irradiation was performed on linear accelerator I-2 at the Center of Collective Use "Kamiks" of ITEP (energy 20 MeV, flux 1·1011 cm–2 ·s–1 , fluence 1·1014 cm–2 ). Optical properties of samples were measured using UV-VisNIR spectrophotometer "Cary-5000" (Agilent Technologies) at non-polarized light taking into account the dichroism (with sample rotation by 90° around the light direction). After irradiation, all samples changed color, become more colored with a grayish tint. Irradiation both with protons and electrons leads to increase of absorption in all investigated wave-length region. The most significant effects are observed in the region of (250-450) nm. The greatest increase in absorption in the region of (250-500) nm is observed after the electron irradiation fluence of 4·1015 cm–2 . The subsequent increase of fluence did not lead to the further increase of absorption.