Strontium tetraborate SrB₄O₇ (SBO) is a promising nonlinear optical material. The merit of this crystal is high mechanical strength (9 Moos) and low hygroscopicity [1]. Nowadays SBO activated with rare earth ions has been intensively studied as a effective material for solid state dosimetry [2]. Recently we have reported photo- and thermoluminescent (TL) properties of polycrystalline powders of strontium tetraborate, activated with different concentration of europium ions (SBO:Eu²⁺). The single crystal SBO:Eu²⁺ is a subject of investigation in this work.

The SBO:Eu²⁺ single crystals were grown by Czochralski method from platinum crucibles in air onto single crystal seed oriented along the [001] direction. The rotation and pulling rates were 20 rpm and 0.25 mm/h, respectively. The axial temperature gradient in the crystallization zone was 70 K/cm. The source charge of SBO:Eu²⁺ was synthesized by solid state reaction [3]. Strontium carbonate SrCO₃ (special purity grade) and boric acid H₃BO₃ (chemical purity grade) in stoichiometric ratio were used as the starting materials. Europium was introduced as oxide Eu₂O₃ (special purity grade).

Macrodefects (inclusions, impurities, cracks) have been investigated by metallographic methods. The system of easy distribution of cracks in SrB4O7 single crystals has been determined. Quality of grown crystals was controlled by results of X-ray analysis. XPA does not reveal any additional phase in samples studied within the limits of experimental error. The grown single crystals had the following crystallographic parameters: rhombic system, space group Pnm2₁, a=10.71171(7) Å, b=4.42687(3) Å, c=4.23481(2) Å, V=200.812(2) ų, Z=2.

The main optical and luminescence properties of SBO:Eu²⁺ single crystals have been studied. It has been shown, that TSL of SBO:Eu²⁺ crystals in the 300 to 500 K range is associated with decay of electron centers (F⁺ centers) localized in non-equivalent positions.

[1] Yu.S. Oseledchik, A.L. Prosvirnin, V.V. Starshenko et al. //J. Cryst. Growth.-1994.-V.135.-P.373-376.

[2] M. Santiago, C. Grassely, E. Caselli et al. //Phys. stat. sol. (a).-2001.-V.185, #2.-P.285-289.

[3] S.V. Parkhomenko, A.V.Tolmachev, M.F. Dubovik, et.al. // Abstracts book, International Conference “CRYSTAL MATERIALS’2005” (ICCM’2005), Kharkov, Ukraine, 2005.

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