Optical and magnetic properties of nanostructured cerium-doped LaMgAl 11 O 19
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Optical and magnetic properties of nanostructured cerium-doped LaMgAl11O19 Ladislav Nádherný1,a) , Václav Doležal1, David Sedmidubský1, Jakub Cajzl1, Romana Kučerková2, Martin Nikl2, Vít Jakeš1, Kateřina Rubešová1 1
Department of Inorganic Chemistry, University of Chemistry and Technology Prague, 166 28 Prague 6, Czech Republic Institute of Physics of the Academy of Sciences of the Czech Republic, 162 00 Prague 6, Czech Republic a) Address all correspondence to this author. e-mail: [email protected] 2
Received: 3 April 2020; accepted: 20 April 2020
Cerium-doped lanthanum magnesium bulk aluminate (La1–xCexMgAl11O19, x = 0.03–0.50; abbreviated as LMA) was prepared via the Pechini sol–gel method after heating at 1200 °C for 2 h. The resulting single-phase ceramics was studied in terms of its structure using X-ray diffraction and optical properties using photoluminescence, its decay time, and radioluminescence spectroscopy. The diffraction and electron microscopy demonstrated LMA’s plate-shaped nanocrystals with structure anisotropy and relatively broad particle size distribution. The optical measurements fully manifested the complexity of the LMA crystal structure. The radioluminescence study of cerium-doped LMA is here presented for the first time and, thus, contributes to the basic knowledge of Ce-doped materials. Additionally, the magnetic susceptibility exhibiting paramagnetic behavior of Ce3+ ions is presented. The magnetic data were interpreted in terms of local atomic Hamiltonian involving the crystal field and the Zeeman effect applied on the ground state J = 5/2 multiplet.
INTRODUCTION Hexagonal aluminates belong to a class of materials with interesting chemical and physical properties [1, 2, 3, 4, 5, 6, 7, 8] and are optically anisotropic due to the P63/mmc group of symmetry [5]. The unit cell of hexagonal aluminates consists of spinel blocks and R-blocks separated by two mirror planes. Large trivalent ions (La3+, Ce3+) occupy 12-fold coordinated sites, while a smaller trivalent ion (Al3+) occupies the octahedral, trigonal bipyramidal, and tetrahedral positions. A divalent ion (Mg2+) shares the tetrahedral positions with a smaller trivalent ion [3, 9]. Hexagonal aluminates, including cerium magnesium aluminates and lanthanum magnesium aluminates doped with rare-earth metals, are currently used as fluorescent lamps with a high quantum yield [1, 4, 10, 11, 12, 13]. Lanthanum magnesium aluminates (LMAs) can be also used as highly efficient lasers [14, 15, 16]. Cerium-doped aluminates with cubic symmetry (yttrium aluminum garnet (YAG), yttrium aluminum perovskite (YAP), and lutetium aluminum garnet (LuAG)) are commercially produced and used as scintillators [17, 18, 19, 20]. LMA is another candidate for the detection of high-energy radiation due to its physical properties, such as a large band gap (6.5 eV) [6] and density (4.285 g/cm3) [5] comparable to
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those of commercially used scintillators. Its melting point (1900 °C) is an important parameter for high-tempera
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