Tin Chloride Sulfates A₃Sn₂(SO₄)_3–xCl_1+2x (A = K, Rb, Cs; x = 0, 1) as Multifunctional Optical Materials

Abstract

The series of alkali-metal tin chloride sulfates A3Sn2(SO4)3–x Cl1+2x (A = K, Rb, Cs; x = 0, 1), K3Sn2(SO4)3Cl, Rb3Sn2(SO4)2Cl3, and Cs3Sn2(SO4)2Cl3, were successfully synthesized through an improved mild hydrothermal method. Interestingly, in addition to the cation size effect, the structure-directing effect of anions induces different symmetries in the three title compounds, with K3Sn2(SO4)3Cl being noncentrosymmetric, while Rb3Sn2(SO4)2Cl3 and Cs3Sn2(SO4)2Cl3 are centrosymmetric. Powder second-harmonic generation (SHG) measurements indicate that K3Sn2(SO4)3Cl is a nonlinear optical material that is type I phase matchable with a weak SHG response (0.1× KDP). Photoluminescence tests reveal that the three title compounds emit strong greenish yellow, orange, and salmon light, respectively, under UV excitation, indicating that they are promising inorganic solid fluorescent materials. Simultaneously, a detailed structural analysis of all the known tin­(II) halide sulfates has been performed, which will guide the systematic exploration of high-performance tin­(II)-based functional materials in the future.

Noncentrosymmetric Rb3(COOH)3(H3BO3)2 vs Centrosymmetric Cs3(COOH)3(H3BO3)2

“…Recently, synthetic chemists have been working on the discovery of NCS functional materials through molecular structure design, such as the rational combination of different local asymmetric units to generate macroscopic asymmetry. − The effective asymmetric units can be divided into the following categories: (1) π-conjugated planar groups such as CO 3 , BO 3 , NO 3 , etc., − (2) tetrahedral units lacking centers such as BO 4 , PO 4 , and SiO 4 tetrahedron, − (3) d 10 cation (Zn 2+ , Cd 2+ , Hg 2+ ) centered polyhedra with highly polar displacement, , (4) Jahn–Teller distortion units containing nonbonded electron pair cations Pb 2+ , Sb 3+ , and Bi 3+ and d 0 cations V 5+ , Mo 6+ , W 6+ , etc. − Among them, the BO 3 unit has been proven to be a classical excellent NLO active group on the basis of the anionic group theory, and several excellent deep or short UV NLO borates displaying a strong NLO coefficient and proper birefringence like β-BaB 2 O 4 (β-BBO), KBe 2 BO 3 F 2 (KBBF), and Pb 2 BO 3 X (X = Cl, Br, I) − have been reported. HCOO – is also an excellent planar candidate for constructing NLO materials, which have been neglected for a long time, and very recently, formates have been proven to be splendid birefringent candidates. , As we know, the combination of two or more planar π-conjugated functional groups into one compound will enhance the optical properties because the synergetic effect of these planar NLO active units is conducive for the superposition of their microscopic linear and nonlinear properties. , However, it should be noted that the introduction of asymmetric units to produce a NCS material is necessary, but there are some other factors that influence the overall centricity, such as the size of the diverse template cations and anions, hydrogen-bonding effect, and the arrangement of the functional groups. , For example, alkali metal cations with discrepant cation sizes often adjust the structures with different symmetries. − …”

Three-dimensional all-inorganic dual halogen emitter Cs2Cd2BrCl5 exhibiting broadband white-light emission

“…Considering the large Stokes shift and wide FWHM, we speculate that the white-light emission of Cs 2 Cd 2 BrCl 5 can be ascribed to STEs. [34][35][36][37] Generally considered, halide luminescent materials exhibit poor structural and photophysical stability. Therefore, the emission spectra of fresh crystals, bulk crystals placed in the air for 120 d and after irradiation for 12 h with 254 nm UV light (300 W cm À2 Xe lamp) were collected.…”

Halogen regulation triggers structural transformation from centrosymmetric to noncentrosymmetric switches in tin phosphate halides Sn2PO4X (X = F, Cl)

“…31,32 In fact, Sn 2+ is not only the birefringence-active unit, but also the NLO-active unit. 33–36 The distorted polyhedra constructed by Sn 2+ usually exhibit large polarizability, which is beneficial for generating a large SHG response. However, regrettably, the overwhelming majority of the reported Sn 2+ -based crystals crystallized in centrosymmetric (CS) space groups.…”