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6
ALT'22 M" LS-P-5
LASER SYSTEMS AND MATERIALS
Effect of isomorphic substitution in the cationic sublattice of langasite family crystals on their optical and electrophysical properties
N. Kozlova1, E. Zabelina1, O. Buzanov2
1 - National University of Science and Technology MISiS, Moscow, Russia 2 - FOMOS-Materials, Moscow, Russia [email protected]
Langasite family crystals are a group of crystals with a calcium-gallium germanate Ca3Ga2Ge4O14 structure, symmetry point group 32, first of all - lanthanum gallium silicate (langasite, LGS, La3Ga5SiO14) and lanthanum gallium tanta-late (langatate, LGT, La3Ga55Ta05O14). Ca3Ga2Ge4O14 structural type was first synthesized in the USSR in the 80th of XX century [1] during the scientific experimental search for new laser media. This structure type allows a wide isomorphic substitution of cations, which allows to be modify the properties of crystals for specific applications.
Langasite family crystals are grown by the Czochralski method from the Ir crucibles mostly in the atmosphere of Ar with addition of oxygen to suppress gallium oxide evaporation [3, 4]. Gallium oxide evaporation leads to the appearance of significant concentrations of gallium and oxygen vacancies, and contributes to the defect formation, especially to F-centers formation, which are observed in these crystals on spectral dependencies of transmission in the form of absorption bands in the region of ~ (480-490) nm, and results in yellow color [5]. The nature of the defect centers in langasite crystals has not yet been definitively determined. Defects in crystals influence electric conductivity and may be observed on the transmission spectra in the form of absorption bands.
Here we present the results of our research of the optical and electrophysical properties of the langasite family crystals with isomorphic substitution in the cationic sublattice.
Crystals with compositions La3Ga55Ta05O14; La3Ga55Ta05O14 doped with Ga2O3 in 2 different concentrations; La3Ga55Ta05O14 dopped with Al; crystals of intermediate composition La3Ga5SiO14 -La3Ga55Ta05O14; La3Ga5SiO14 were grown and samples were prepared at FOMOS-Materials.
Optical and electrophysical parameters of crystals were studied in the accredited testing laboratory «Single crystals and Stocke on their base» of NUST MISIS. Spectral dependences of the transmission of samples were obtained at t = 300 K on the UV-Vis-NIR spectrophotometer Cary-5000 (Agilent Technologies) in the wavelength range (200 - 800) nm. Temperature dependences of specific electrical conductivity (electrical resistance) were measured with an electrometer Keithley Instruments model 6517A.
[1] B.V. Mill, A.V. Butashin, G.G. Khodzhabagyan, E.A. Belokoneva, N.V. Belov, Modified rare-earth gallates with the structure Ca3Ga2Ge4O14, Reports of the Academy of Sciences of the USSR, 264 (1982) 1385 - 1389.
[2] B.V. Mil1', Z.A. Kazei, D.M. Tsymbarenko Formation of Phases with the Ca3Ga2Ge4O14 Structure in Ln2O3-M2O3-GeO2-BeO (Ln = La-Gd, M = Ga, Al, Fe, Cr) Systems, Russian Journal of Inorganic Chemistry, 63 (2018) 1283-1290
[3] O.A. Buzanov, A.V. Naumov, V.V. Nechaev, S.N. Knyazev 54 A new approach to the growth of langasite crystals, Proc. 1996 IEEE Int. Freq. Control Symp, (1996) 131-136.
[4] S. Uda, S.Q. Wang, N. Konishi, H. Inaba, J. Harada Growth habits of 3 and 4-inch langasite single crystals, Journal of Crystal Growth, 237-239 (2002) 707-713.
[5] E. Zabelina thesis «Inhomogeneities in lanthanum-gallium tantalate crystals and their influence on optical properties» (date of defense 31.05.2018, date of approval 12.12.2018), supervisor: Ph.D., senior researcher Kozlova N.S.
