Graphical Ba 3 Sc 2 (BO 3 ) 4 displays a beneficial layered structure in which BO 3 units are parallelly arranged by the modulation of ScO 6 octahedra and BaO n (n=9, 12) polyhedrons. The parallel arrangement of planar BO 3 units generates a large basic birefringence of 0.096, further enhanced by distorted ScO 6 octahedra up to Δn=0.149@550 nm, which is similar to the values reported in TiO 2 , LiNbO 3 , BaTi(BO 3 ) 2 . Transition metal ions with d 0 electronic states (Ti 4+ , Zr 4+ , Nb 5+ and Ta 5+ ) are widely investigated as functional materials. This work first illustrates that Sc 3+ ion, long-time ignored, displays a second-order Jahn-Teller (SOJT) effect similar to asymmetric oxide-coordinated transition metal ions, thus providing a new ground to seek for asymmetric functional materials with enhanced performances. In Ba 3 Sc 2 (BO 3 ) 4 , BO 3 groups are parallelly arranged, satisfying the ideal arrangement to produce large birefringence. Importantly, distorted octahedral ScO 6 with Sc 3+ ion in its d 0 electronic state enlarges birefringence unexpectedly up to 0.149 @ 550 nm, which is larger than previously reported borates containing solely BO 3 , even to B 3 O 6 units. Subsequently, the SOJT influence of distorted ScO 6 octahedra on birefringence is verified by a comparison between experimental data and theoretical calculations. In addition, Ba 3 Sc 2 (BO 3 ) 4 also displays a high transmittance in the range of 230 nm–3.5 μm with a UV cut-off wavelength at 198 nm and a large laser induced damage threshold (2.7 GW/cm 2 ), comparable to α-BaB 2 O 4 . Above characteristics imply that the title compound may be a promising birefringent material.
The design and development of colorimetric sensors for recognition of rare-earth Sc 3+ ions are very challenging and most of the reported methods are limited by poor sensitivity and serious interference. Herein, we unveiled a new colorimetric strategy for the sensitive and selective detection of Sc 3+ based on the surface plasmon resonance properties of gold nanoparticles (GNPs). The key aspect of the proposed protocol is the selection of pyridoxal phosphate (PLP), an important biomolecule involved in many biological processes, both as an effective aggregation promoter of GNPs stabilized by cysteamine (Cyst-GNPs) and a strong chelator for the selective complexation of Sc 3+ . PLP can covalently bind to the Cyst-GNPs through the formation of a Schiff base, which neutralizes the positive surface charges, weakens the electrostatic repulsion force among the nanoparticles, thereby triggering the agglomeration of Cyst-GNPs. Owing to the intensive Lewis acid-base interactions, the introduced Sc 3+ ions effectively compete with Cyst-GNPs to bind PLP, and the Cyst-GNPs tend to be dispersed in this case. A linear response from 0.1 to 3 μM is achieved for Sc 3+ , and a detection limit down to 0.02 μM is obtained. Negligible interfere from other ions is observed in this assay under identical experimental conditions.
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