(3 + 1)-Dimensional commensurately modulated structure and photoluminescence properties of diborate KSbOB₂O₅.

Single-crystal diborate KSbOB2O5 has been prepared under a high temperature molten-salt method and its structure has been determined by single crystal X-ray diffraction analysis. The diffraction pattern shows strong main reflections and weak satellite reflections, clearly indicating a modulated structure. Using the four-dimensional superspace formalism for aperiodic structures, its reflections could be indexed as orthorhombic superspace group Pmn2₁(0β0)s00 with the modulation vector q = 5/12b*, and then the structure solution and refinement reached a final commensurately modulated model that was refined extremely well and did not show any unusual features. On the other hand, the powder sample of KSbOB2O5 was synthesized by the high-temperature solid-state reaction method, and the powder X-ray diffraction pattern fits very well with the simulated from the single-crystal data. In addition, photoluminescence properties of diborate KSbOB2O5 activated by 4.5 mol% Dy(3+) have been studied, indicating an extraordinary phenomenon that the red emission at around 635 nm ((4)F(9/2) → (6)H(11/2)) is much stronger than the yellow emission at around 581 nm ((4)F(9/2) → (6)H(13/2)).