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

• New nonlinear-optical rare-earth binary borate Rb 3 SmB 6 O 12 was prepared by the solid state reaction method. • Rb 3 SmB 6 O 12 crystallized in noncentrosymmetric space group R 32. • The incongruent melting of Rb 3 SmB 6 O 12 is observed at 1104 K with as high melting enthalpy as H m = –161.5 J/g. New noncentrosymmetric alkali rare-earth double borate Rb 3 SmB 6 O 12 was found in the ternary system Rb 2 O–Sm 2 O 3 –B 2 O 3 . The Rb 3 SmB 6 O 12 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. Rb 3 SmB 6 O 12 crystallized in space group R 32 with unit cell parameters a = 13.4874 (3) and c = 30.9398 (6) Å, V = 4874.2 (2) Å 3 , Z = 15. In the three-dimensional framework structure of Rb 3 SmB 6 O 12 , each [B 5 O 10 ] 5− group is linked to four different Sm-O polyhedra and, likewise, each Sm-O polyhedron is connected to four neighboring [B 5 O 10 ] 5− groups. The Sm-O polyhedra are formed by the face-sharing linked SmO 6 octahedra. Rb + cations are located in large cavities of the framework structure. From the thermal stability measurements, the incongruent melting of Rb 3 SmB 6 O 12 is observed at 1104 K with as high melting enthalpy as H m = –161.5 J/g. The nonlinear optical response of Rb 3 SmB 6 O 12 tested via SHG is estimated to be similar to that of K 3 YB 6 O 12 . The Raman spectrum of Rb 3 SmB 6 O 12 is mainly governed by the vibrations of BO 4 and BO 3 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 Rb 3 SmB 6 O 12 structural units. The luminescence spectrum of Sm 3+ ions in the specific local environment of the Rb 3 SmB 6 O 12 crystal lattice shows the ability to control the individual band intensity ratio originating from 4 G 5/2 level.