Synthesis,Crystal Structures And Optical Properties Of Inorganic Phosphates/Borates

Inorganic phosphate/borate crystal materials have attracted much interest because of their diverse structures and the variety of applications such as luminescence,nonlinear optics,and ferro/piezoelectricity.Currently,a majority of reported inorganic phosphates/borates were synthesized by the high temperature solid state method,therefore it is still a keypoint to explore the mild experimental methods for the preparation of the novel inorganic phosphate/borate crystal materials with excellent properties.Here in this work,we aim at designing and synthesizing the new inorganic phosphate/borate optical crystals,take the heterometallic tin?II?-phosphates,the alkali metal germanophosphates?GePOs?,and the alkaline earth metal borate-fluoride as the research objects,and synthesized three series of compounds with different structures by adopting the hydrothermal,the solvothermal and the surfactant-thermal methods.The structures were characterized by the single crystal X-ray diffraction,powder X-ray diffraction?PXRD?,thermogravimetric analysis?TGA?,the fourier transform infrared spectrometer?FT-IR?and the UV-Vis-NIR diffuse reflectance spectrometer.Their optical properties were examined by the solid-state luminescence test and the second harmonic generation?SHG?measurement.The results of this paper are as follows:?1?By choosing the Sn²⁺cations as the research object,two heterometallic tin-phosphates crystal materials:Sn₂Ge?PO₄?₂?OH?₂?1?and Sn₂Mn?PO₄?₂?2?were synthesized by the hydrothermal and solvothermal methods,respectively.Compound 1features a three-dimensional?3D?structure which is constructed from 1D chains of[Ge?PO₄?₄?OH?₂]_?linked to each other through Sn-O bonds,compound 2 features a 3D framework composed of a 2D[Sn₂O₂?PO₄?₂]_?layer in the bc plane and MnO₆ octahedra connected with the adjacent layers,TGA results show that the anhydrous compound 2 has a high thermal stability in the range of 30-800°C,their photoluminescence study indicates that1 exhibits a green luminescent emission under UV excitation,2 exhibits a blue luminescent emission under UV excitation,respectively.?2?By choosing RbBr and CsBr as the alkali metal sources,two alkali metal germanophosphates?GePOs?crystals:Rb₃Ge₂?HPO₄?₅?H₂PO₄??3?and CsGe?HPO₄?₂?OH??4?were synthesized by the solvothermal method.Compound 3 shows 1D chains of[Ge?HPO₄?₆]_?along the c-axis formed by the GeO₆ octahedra and co-edge PO₄ tetrahedra,Rb⁺cations filled between chains for the charge balance;Compound 4 exhibits 1D chains of[Ge?HPO₄?₄?OH?₂]_?constructed by the adjacent Ge?HPO₄?₄?OH?₂ octahedra,the Cs⁺cations filled between chains for the whole charge balance.The diffuse reflectance of compound 3 at200 nm is 64%,the diffuse reflectance of compound 4 at 200 nm is 84%,the experimental optical band gaps of 3 and 4 are 4.66 eV and 5.93 eV,respectively,which indicated that both 3and 4 are good wide band-gap semiconductors,the corresponding absorption cut-off edges are266 nm and 209 nm,respectively.?3?By choosing Ba?NO₃?₂ as alkaline earth metal source,an alkaline-earth metal borate-fluoride crystal material,Ba[BO?OH?₂]F?5?was prepared by the surfactant-thermal method.Compound 5 shows a double-layered structure formed by the Ba-F-Ba bonding of the[Ba?BO?OH?₂?]_?layers,the diffuse reflectance of compound 5 at 200 nm is 62%,and the experimental optical band gap of compound 5 is 5.35 eV,the SHG measurement indicated that the compound 5 can achieve type-I phase matching under the excitation of 1064 nm.the SHG of compound 5 is about 0.8 times of that of KH₂PO₄?KDP?crystal when the crystal size is 105-150?m,indicating that compound 5 could be potentially applied in the UV nonlinear optics area.