Crystal structures and photoluminescence properties of two novel sorosilicates with an unprecedented ratio of di- and trisilicate groups: Ba2Ho10(Si2O7)3(Si3O10)2 and isotypic Ba2Er10(Si2O7)3(Si3O10)2

Abstract Ba 2 Ho 10 (Si 2 O 7 ) 3 (Si 3 O 10 ) 2 and isotypic Ba 2 Er 10 (Si 2 O 7 ) 3 (Si 3 O 10 ) 2 represent a new mixed-framework structure type with an unprecedented ratio of di- and trisilicate groups among silicates. The atomic arrangement features asymmetric zigzag chains of edge-sharing Ln 3+ O 6 (Ln = Ho, Er) octahedra corner-linked by isolated Si 2 O 7 and horseshoe-shaped Si 3 O 10 groups in the ratio of 3:2. Single-crystal X-ray diffraction investigations yielded the triclinic space group P 1 ¯ (no. 2), with a = 5.5494(11)/5.5360(11) A, b = 6.8795(14)/6.6870(13) A, c = 23.703(5)/23.691(5) A, α = 83.60(3)/83.64(3)°, β = 88.80(3)/88.77(3)°, γ = 73.43(3)/73.38(3)°, V = 861.9(3)/835.2(3) A 3 , R ( F ) = 0.0289/0.0559, respectively. The laser-induced photoluminescence emission of trivalent holmium und erbium in both framework silicates was studied using a dispersive single-stage spectrometer and compared to the emission spectra of other framework Ba-Er and Ba-Ho silicates. The 4 S 3/2 → 4 I 15/2 transition of Er in Ba 2 Er 10 (Si 2 O 7 ) 3 (Si 3 O 10 ) 2 causes a photoluminescence emission in the visible green spectral range whereas its Ho representative with the 5 F 3 → 5 I 7 transition in the red spectral region.