ИСТИНА

Langasite-type crystals such as langasite La3Ga5SiO14 (LGS), langatate La3Ga5,5Ta0,5O14 (LGT) and catangasite Ca3TaGa3Si2O14 (CTGS) are characterised by calcium-gallogermanate (Ca3Ga2Ge4O14) structure (point group 32). These crystals are piezoelectric, not pyro- and ferroelectric, not hygroscopic, show no phase transitions up to the melting point about 1500 oC, they are birefringent and gyrotropic. The possibility of wide isomorphic substitution of cations within this crystal type enables to tailor crystals properties and engineer specific crystals composition for particular applications. The origin of intrinsic defects and relationship between composition and properties in this crystal type are still not clear. Optical and luminescence properties are extremely sensitive to the crystal structure defects in langasite-type crystals. Here, we present the results of our study of the optical and luminescence properties of LGS, LGT and CTGS crystals irradiated by electron, proton and neutron beams. All investigated samples were provided by JSC "Fomos-Materials" Co. Electron irradiation was performed at the Center of Physical Measurements Investigations of IPCE RAS using the linear accelerator (energy 5 MeV, flux 4·1012 cm–2·s–1). Proton irradiation was performed on linear accelerator I-2 at the Center of Collective Use "Kamiks" of ITEP (energy 20 MeV, average flux 1·1011 cm–2·s–1). Neutron irradiation was performed at the JSC "SSC RF – IPPE" using two-zone pulsed self-extinguishing fast-neutron reactor (average neutron energy 1,25 MeV). Optical properties were studied in Accredited Testing Laboratory "Single Crystals and Stock on their Base" of NUST "MISiS" using Cary 5000 spectrophotometer with "UMA" accessory (Agilent Technologies). The measurements of the luminescence characteristics of the crystals was performed in the Skobeltsyn Institute of Nuclear Physics using laboratory set-up with 150 W xenon lamp was used as an excitation source. The luminescence was registered using LOT-Oriel MS-257 spectrometer equipped with CCD detector.