Structural and spectroscopic properties of new noncentrosymmetric self-activated borate Rb3EuB6O12 with B5O10 units

New noncentrosymmetric double borate Rb3EuB6O12 was designed and synthesized by the solid state reaction method, and its crystallographic parameters were obtained by Rietveld analysis. This borate crystallizes in the trigonal space group R32 with cell parameters a = 13.4604(2) Å, c = 30.7981(5) Å, Z = 15. Its structure features a three-dimensional framework composed of the [B5O10]5 − groups that are bridged by Eu-O polyhedra. The existence of B5O10 group in the structure was confirmed by vibrational spectroscopy. Rb3EuB6O12 melts incongruently at 1101 K. The second harmonic generation effect of Rb3EuB6O12 is 16 times higher than that of the α-quartz standard. In the luminescence spectrum, the domination of a single prominent narrow line from the hypersensitive 5D0 - 7F2 manifold of Eu3 + ions is observed, while the 5D0 - 7F1 manifold and ultranarrow 5D0 - 7F0 line are of comparable peak intensity. These features are explained by a specific local symmetry of the Eu3+ ion within the crystal structure of Rb3EuB6O12