Synthesis,Crystal Structures And Second-Order Nonlinear Optical Properties Of Novel Ultraviolet And Deep-ultraviolet Borates

The discovery and commercialization of ultraviolet?UV?and deep-ultraviolet?deep-UV?second-order nonlinear optical?NLO?inorganic crystals have been achieved.Although these crystals have been widely used in electro-optic devices,some drawbacks limit their practical usage.The exploration of these NLO crystals with high-performance is currently a high profile topic in the fields of solid-state chemistry.In order to develop novel UV and deep-UV NLO metal botates,eleven crystals with noncentrosymmetric?NCS?structures were obtained under mild synthetic conditions.Crystal structures and properties were characterized.Band structures and density of states as well as the electron density distributions were systematic investigated based on density functional theory calculations.The main contents of the dissertation are as following:1)Synthesis,crystal structure and properties of deep-UV NLO broates MN₃?OH?(B₉O₁₆)[B?OH?₄]?M=Li,N=Ba;M=Na,N=Sr?Two new alkali metal-alkaline earth metal borates,MN₃?OH?(B₉O₁₆)[B?OH?₄]?M=Li,N=Ba;M=Na,N=Sr?,were obtained via convenient hydrothermal methods.The structure exhibits a three-dimensional?3D?zeolite-like framework consisting of B₉O₁₉ units.The Sr²⁺and Na⁺ions in the structure of NaSr₃?OH?(B₉O₁₆)[B?OH?₄],residing in the cavities of the anionic framework,act as templates for the assembly of NLO-active groups in a more aligned arrangement,and thereby an optimal balance between enhanced SHG activity and wide-UV transparency.The absorption edges are reported to be below 200 nm.Second-harmonic generation?SHG?measurements show that both compounds is type I phase-matching in the wavelength of 1064 nm and 532 nm with SHG response 1.2×KH₂PO₄?KDP?for Li Ba₃?OH?(B₉O₁₆)[B?OH?₄]and3.2×KDPforNaSr₃?OH?(B₉O₁₆)[B?OH?₄].Structure-property relationships were analysed based on density functional theory calculations.Calculations on dipole moments and SHG-weighted electron densities reveal that the significant SHG response in NaSr₃?OH?(B₉O₁₆)[B?OH?₄]originates from the virtual electronic transitions inside the BO₄ and B₉O₁₉ groups.2)Synthesis,crystal structures and properties of two alkali/alkaline-earth metal borates Ba₂[B₄O₇?OH?₂]and NaB₅O₇?OH?₂?H₂O?Two novel NCS metal borates,Ba₂[B₄O₇?OH?₂]and Na[B₅O₇?OH?₂]?H₂O?,were synthesized via hydrothermal and surfactant-thermal methods,respectively.The structure of Ba₂[B₄O₇?OH?₂]exhibits new 1D borate chains constructed from B₃O₉ and B₃O₈ rings,which are interconnected via Ba-O bonds to generate a 3D network.The structure of Na[B₅O₇?OH?₂]?H₂O?consists of double helical chains formed from B₅O₁₀ units,assembled into a 3D network via Na⁺cations and H-bonding interactions.The absorption edges of aforementioned materials are 242 and 221 nm,respectively.SHG measurements indicate that Ba₂[B₄O₇?OH?₂]is type I phase-matching,and shows an SHG response of 2.2×KDP,while Na[B₅O₇?OH?₂]?H₂O?exhibits a weak SHG efficiency.Theoretical calculations on two materials employing DFT methods have been performed to rationalize the electron density and density of states as well as band structure.The surfactant-thermal method was firstly applied to synthesize metal borate crystal,which could enrich the diversity of SHG-active metal borates.3)Synthesis,crystal structures and properties of three mixed-alkali-metal boratesAseriesofmixed-alkali-metalboratesNaK?B₅O₈??OH?·H₂O,NaK₆[?B₄O₅??OH?₄]₃?OH?·C₂H₅OH and Na_0.33K_1.67?B₄O₅??OH?₄·3H₂O were solvothermally synthesized via different polar organic solvents.The structure of NaK?B₅O₈??OH?·H₂O exhibits a 2D-layered network formed by B₅O₁₁ units,extending to a 3D framework via K-O and Na-O bonds.The structure of NaK₆[?B₄O₅??OH?₄]₃?OH?·C₂H₅OH consists of isolated B₄O₉ units connected by Na-O,K-O bonds and H-bonding interactions,generating a 3D supramolecular framework.Na_0.33K_1.67?B₄O₅??OH?₄·3H₂O crystallizes in NCS space group,and its NLO properties are performed for the first time.SHG measurements indicate that Na_0.33K_1.67?B₄O₅??OH?₄·3H₂O is type I phase-matching and exhibits a moderate SHG response0.94×KDP.The absorption edge of Na_0.33K_1.67?B₄O₅??OH?₄·3H₂O is 242 nm,which confirms that Na_0.33K_1.67?B₄O₅??OH?₄·3H₂O is a potential NLO material in UV region.4)Synthesis,crystal structures and properties of two mixed-alkali-metal borophosphates Na₄MB₂P₃O₁₃?M=Rb,Cs?The first NCS mixed-alkali-metal borophosphates,Na₄MB₂P₃O₁₃?M=Rb,Cs?,were obtained using a low-temperature flux mean.The two compounds are isostructural,consisting of new 1D borophosphate chains built from B₂P₃O₁₄ units,extending into a 3D network by alkali metal ions.The absorption edges of Na₄MB₂P₃O₁₃?M=Rb,Cs?are 276 and 267 nm,respectively.SHG measurements indicate that Na₄MB₂P₃O₁₃?M=Rb,Cs?are type I phase-matching,with SHG responses 0.35 and 0.42×KDP,respectively.Theoretical calculations identify that the optical properties of Na₄MB₂P₃O₁₃?M=Rb,Cs?arise from the BO₄ and PO₄ anionic groups.5)Synthesis,crystal structures and properties of two rare earth-metal borates Sc₂B₂O₅F₂and Lu?B₆O₉??OH?₃Two new borates,CS Sc₂B₂O₅F₂ and NCS Lu?B₆O₉??OH?₃,were synthesized from a low-temperature flux method.The structure of Sc₂B₂O₅F₂ features a 3D framework built by B₂O₅ units via Sc-O/Sc-F bonds;while the structure of Lu?B₆O₉??OH?₃ contains B₆O₁₅ units and exhibits a 3D framework with Lu³⁺cations presenting in the cavities.The absorption edges of Sc₂B₂O₅F₂ and Lu?B₆O₉??OH?₃ are 227 and 351 nm,respectively,which well confirms that introduction of F^-anions into borates can effectively increase the UV transparency range.SHG measurements reveal that Lu?B₆O₉??OH?₃ is type I phase-matching with SHG response 2×KDP,indicating Lu?B₆O₉??OH?₃ may have potential applications in the UV region.