Pure and RE 3+ -Doped La 7 O 6 (VO 4 ) 3 (RE = Eu, Sm): Polymorphism Stability and Luminescence Properties of a New Oxyvanadate Matrix

• Published in: Inorganic chemistry 2020-05, Vol.59 (9), p.5929-5938
• Main Authors: Gómez Torres, María Alejandra, Gauthier, Gilles H, Kaczmarek, Anna M, Huvé, Marielle, Roussel, Pascal, Dupray, Valérie, Yuan, Lina, Zadoya, Anastasiya, Colmont, Marie
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.9b03689

Two polytypes of the new oxyvanadate matrix La O (VO ) were identified and deeply characterized. The crystal structure of the α-polytype was solved using a combination of precession electron diffraction and powder X-ray diffraction (XRD) techniques. It crystallizes in a monoclinic unit cell with space group 2 , = 13.0148(3) Å, = 19.1566(5) Å, = 7.0764(17) Å, and β = 99.87(1)°. Its structure is built upon [La O ] polycationic units at the origin of a porous 3D network, evidencing rectangular channels filled by isolated VO tetrahedra. An high-temperature XRD study highlights a number of complex phase transitions assorted with the existence of a β-polytype also refined in a monoclinic unit cell, space group 2 / , = 13.0713(4) Å, = 18.1835(6) Å, = 7.1382(2) Å, and β = 97.31(1)°. Thus, during the transitions, while the polycationic networks are almost identical, the vanadate's geometry is largely modified. The use of Eu and Sm at different concentrations in the host lattice is possible using solid-state techniques. The photoluminescence (PL), PL excitation (PLE) spectra, and luminescence decay times were recorded and discussed. The phosphors present an emission light, being bright and reddish orange after excitation under UV. This is mainly due to the V-O band and f-f transitions. Whatever the studied polytype, the final luminescence properties are retained during the heating/cooling process.