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The series of alkali-metal tin chloride sulfates A 3 Sn 2 (SO 4 ) 3- x Cl 1+2 x (A = K, Rb, Cs; x = 0, 1), K 3 Sn 2 (SO 4 ) 3 Cl, Rb 3 Sn 2 (SO 4 ) 2 Cl 3 , and Cs 3 Sn 2 (SO 4 ) 2 Cl 3 , 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 K 3 Sn 2 (SO 4 ) 3 Cl being noncentrosymmetric, while Rb 3 Sn 2 (SO 4 ) 2 Cl 3 and Cs 3 Sn 2 (SO 4 ) 2 Cl 3 are centrosymmetric. Powder second-harmonic generation (SHG) measurements indicate that K 3 Sn 2 (SO 4 ) 3 Cl 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.

In this work, BaYF 5 :20%Yb 3+ /2%Er 3+ / x %Bi 3+ (abbreviated as BaYF 5 :Yb,Er,Bi x , where x = 0-3.0) upconversion nanoparticles (UCNPs) with various doping concentrations of Bi 3+ were synthesized through a simple hydrothermal method. The influence of the doping amount of Bi 3+ on the microstructures and upconversion luminescence (UCL) properties of the BaYF 5 :Yb,Er,Bi x UCNPs was studied in detail. The doping concentration of Bi 3+ has little influence on the microstructures of the UCNPs but significantly impacts their UCL intensities. Under excitation of a 980 nm near-IR laser, the observed UCL intensities for the BaYF 5 :Yb,Er,Bi x UCNPs display first an increasing trend and then a decreasing trend with an increase in the ratio x , giving a maximum at x = 2.5. A possible energy-transfer process and simplified energy levels of the BaYF 5 :Yb,Er,Bi x UCNPs were proposed. The potential of the BaYF 5 :Yb,Er,Bi x UCNPs as contrast agents for computerized tomography (CT) imaging was successfully demonstrated. An obvious accumulation of BaYF 5 :Yb,Er,Bi x in tumor sites was achieved because of high passive targeting by the enhanced permeability and retention effect and relatively low uptake by a reticuloendothelial system such as liver and spleen. This work paves a new route for the design of luminescence-enhanced UNCPs as promising bioimaging agents for cancer theranostics.