Exploration of structural, thermal and vibrational properties of new noncentrosymmetric double borate Rb3Tm2B3O9

Double borate Rb3Tm2B3O9 was newly synthesized by solid-state reaction. The crystal structure of Rb3Tm2B3O9 was refined by Rietveld's method: Pna21, a = 8.6648(1), b = 9.5238(1), c = 12.1722(1) Å, Z = 4. The crystal structure of Rb3Tm2B3O9 consists of -[Tm2O9]∞- chains along the “a” axis. BO3 triangles linked chains in a three-dimensional framework. Rubidium atoms occupied empty ones in channels. The thermal behavior of Rb3Tm2B3O9 was studied in detail in between 25 and 1200 °C by DSC and TG methods. Rb3Tm2B3O9 was congruently melted at 886 °C. The band gap is found as Eg ∼5.14 eV. Nonlinear optical response of Rb3Tm2B3O9 tested via SHG is estimated to be lower than that of KDP. The existence of BO3 groups in Rb3Tm2B3O9 crystal structure has been confirmed by an IR analysis. [Display omitted] •New noncentrosymmetric double rubidium holmium borate – Rb3Tm2B3O9 was discovered and explored.•Rb3Tm2B3O9 crystallized in space group Pna21 as shown by Rietveld analysis.•A detailed study of the temperature behavior revealed congruent melting at 886 °C and decomposition into RbBO2 and Tm2O3.•The band gap value is 5.14 eV and was obtained by the Tauc method in direct mode.•The intensity of SHG signal for Rb3Tm2B3O9 was 0.5 times as that of KDP.