Magnetic Resonance Study of Non-Equivalent Centers Created by 4f-Ions in Congruent and Stoichiometric Lithium Niobate
- PDF / 3,711,024 Bytes
- 12 Pages / 612 x 792 pts (letter) Page_size
- 86 Downloads / 166 Views
1111-D01-03
Magnetic Resonance Study of Non-Equivalent Centers Created by 4f-Ions in Congruent and Stoichiometric Lithium Niobate Galina Malovichko1, Valentin Grachev1, Jonathan Jorgensen1, Martin Meyer1, Mark Munro1, Benjamin Todt1, Ian Vrable1, Edward Kokanyan2, Viktor Bratus3 and Sergey Okulov3 1 Physics Department, 264 EPS, Montana State University, Bozeman, MT 59717, U.S.A. 2 Institute of Physical Researches, Ashtarak, Armenia 3 Institute of Semiconductor Physics, Kiev, Ukraine ABSTRACT Lithium Niobate doped with 4f-ions is of great interest for both fundamental science and advanced applications including high efficiency lasers with frequency conversion, elements for an all-optical telecommunication network and quantum cryptography. Our study has shown that 4f-ions create an unexpected variety of completely different non-equivalent centers in both stoichiometric and lithium deficient congruent crystals. Dominant Nd1 and Yb1 centers have C3 point symmetry (axial center), whereas all Er and most other Nd and Yb centers have the lowest C1 symmetry. Distant defects create small distortions of the crystal field at the impurity site, which cause line broadening, but do not change the C3 symmetry of observed EPR spectra. Defects in the near neighborhood can lower center symmetry from C3 to C1. We concluded that Nd1 has distant charge compensation, whereas the charge excess in low-symmetry Nd(Li) centers is compensated by near lithium or niobium vacancies. Since no axial centers were found for Er, models with cation vacancies can not describe our experimental data. The dominant axial Yb1 center has no defects in its surrounding. One axial and one low-symmetry Yb centers are self compensating Yb(Li)-Yb(Nb) pairs. Six other centers are different complexes of Yb3+ and intrinsic defects. Obtained data can be used for defect engineering for tailoring properties of photonic materials. INTRODUCTION Lithium Niobate (LN) doped with 4f-ions is of great interest for both fundamental science and advanced applications including high efficiency lasers with frequency conversion, elements of an all-optical telecommunication network and quantum cryptography. Conventional LN crystals, grown from a congruent melt with lithium deficiency (Xmelt = XCrystal ≈ 48.4%, where X = [Li]/([Li]+[Nb]), contain some percent of intrinsic (non-stoichiometric) defects like antisites, lithium and niobium vacancies and their complexes, and, consequently, have strong structural disorder (Fig. 1). Crystals grown under special conditions from melts to which potassium has been added have significantly lower intrinsic defect concentrations. These samples, named stoichiometric or nearly stoichiometric (sLN), have physical properties which are often very different from properties of congruent samples. According to data of the Extended X-ray Absorption Fine Structure Analysis, EXAFS [1], and Rutherford back scattering data [2, 3, 4, 5, 6, 7], most trivalent ions substitute for Li (with some displacement from Li site) and should create similar centers. However, s
Data Loading...
