Design And Syntheses Of New Inorganic Metal Selenites With Second-Order NLO Property

The presence of the active lone-pair electrons of Se4+ cation which are susceptible to the second-order Jahn-Teller(SOJT)distortion could make the oxygen ligends adopting the so called "one side" coordinating mode,resulting the central cation of Se4+in an asymmetric environment.So,the SeO3 group was considered to be a kind of second-harmonic generation(SHG)active groups.Compared to tellurites and iodates,the SHG efficiencies of metal selenites are very weak because the dipole moments of SeO3 groups are usually less than the corresponding TeO3 and IO3 groups.Our efforts were devoted to improve the SHG efficiency of inorganic metal selenites.In this thesis,our work were focused on introducing d0 transition metal ions of Mo(?)and F-,?-conjugated NO3 nitrate planar triangle and phosphate tetrahedron into metal selenite compounds.New inorganic metal selenites with novel structures and strong SHG efficiencies were abtained by the synergetic polarization effects of the introduced second SHG-active groups and the SeO3 groups.Specifically,eleven new inorganic metal selenites have been synthesized successfully by hydrothermal reactions and high-temperature solid-state techniques.Single crystal X-ray diffraction,powder X-ray diffraction,IR spectra,energy dispersive X-ray spectroscope and powder SHG measurements,etc.have been preformed to determine their composition,crystal structures and SHG properties.The main results are summarized as follows:(1)Seven new inorganic metal selenite typed SHG materials,namely,Ln2Mo206(Se03)2(H20)F2[Ln = Sm(1),Eu(2),Gd(3),Tb(4),Dy(5)],BaMo2Se2O10F2(6)and BaMo2Sei,37Te0.63O10F2(7),were obtained by introduing Mo(VI)and F-ions into Ln/Ba-Se(IV)-O systems.Compounds 1-5 are crystallized in polar space group of Pmn21 and their SHG efficiencies are about 5.1,6.9,9.8,11.2 and 5.9 times that of KDP(KH2PO4),respectively.To the best of our knowledge,the SHG efficiency of Tb compound is the largest in lanthanide selenites system.Isostructural compounds 6 and 7 are crystallized in polar space group of Aba2.The SHG efficiency of compound 6 is about 2.7 times that of KDP.(2)Four new inorganic metal selenites containing NO3 or PO4 groups,namely,PbCdF(Se03)(N03)(8),Cd7(HPO4)2(PO4)2(SeO3)2(9),Cd6(PO4)1.34(SeO63)4.66(10)and Zn3(HPO4)(SeO3)2(H2O)(11),were obtained by high temperature solid state method and hydrothermal reactions.Compound 8 is crystallized in polar space group of Pca21 and Its SHG efficiency is about 2.6 times that of KDP.Compounds 9-11 are crystallized in centrosymmetric space group and not SHG-active.However,compared with the reported metal selenites,these compounds exhibit large band gap of 4.69,5.07 and 5.63 eV,respectively,which is benefit to the design of new metal selenites based SHG materials with high laser induced damage threshold.