New double nonlinear-optical borate Rb3SmB6O12: Synthesis, structure and spectroscopic properties

Abstract

New noncentrosymmetric alkali rare-earth double borate Rb3SmB6O12 was found in the ternary system Rb2O–Sm2O3–B2O3. The Rb3SmB6O12 powder was prepared by the solid state reaction method at 750 °C for 40 h and the crystal structure was obtained by the Rietveld method. Rb3SmB6O12 crystallized in space group R32 with unit cell parameters a = 13.4874 (3) and c = 30.9398 (6) Å, V = 4874.2 (2) Å3, Z = 15. In the three-dimensional framework structure of Rb3SmB6O12, each [B5O10]5− group is linked to four different Sm-O polyhedra and, likewise, each Sm-O polyhedron is connected to four neighboring [B5O10]5− groups. The Sm-O polyhedra are formed by the face-sharing linked SmO6 octahedra. Rb+ cations are located in large cavities of the framework structure. From the thermal stability measurements, the incongruent melting of Rb3SmB6O12 is observed at 1104 K with as high melting enthalpy as Hm = –161.5 J/g. The nonlinear optical response of Rb3SmB6O12 tested via SHG is estimated to be similar to that of K3YB6O12. The Raman spectrum of Rb3SmB6O12 is mainly governed by the vibrations of BO4 and BO3 borate groups observed over the wavenumber range of 287–1550 cm–1. The spectral bands below 270 cm–1 were attributed to rotational, translational and mixed vibrations of Rb3SmB6O12 structural units. The luminescence spectrum of Sm3+ ions in the specific local environment of the Rb3SmB6O12 crystal lattice shows the ability to control the individual band intensity ratio originating from 4G5/2 level.