Syntheses,Structures And Nonlinear Optical Properties Of Novel Iodates

Second-Harmonic-Generation（SHG）nonlinear optical（NLO）crystal plays a vital role in tunable lasers,optical communications,medical treatment,precision manufacturing,national defense,military affairs and so on.As a NLO crystal,inorganic materials have been applied in the most field due to their excellent stability and machinability.Iodate is an important-inorganic NLO crystal,in which the IO₃ functional group is a distorted-triangular cone due to the effect of second-order Jahn-Taylor.Therefore,it is easy to form a non-centrosymmetric（NCS）structure and a strong SHG effect.And iodates have rich structures including different metallic and non-metallic elements,so a large number of NCS iodates have been reported in the past decades.And the systematic database of NCS iodate has been formed as an early version.In this paper,we summarized reported NCS iodates,and two studies were carried out to fill some gaps in database of NCS iodates.As a result,three novel NCS iodates were synthesized by hydrothermal method as follows:Firstly,we synthesized two novel isostructural cerium iodates,K₃Ce₉（IO₃）₃₆ and La_0.3Ce₉（IO₃）₃₆,they are intermediate-valent compounds with R3c space group,which proved by crystal structure,elemental analysis and electron paramagnetic resonance（EPR）spectra.They are stable up to 430°C and have same bandgap of 2.3 e V.The SHG intensity is 0.4×KDP for K₃Ce₉（IO₃）₃₆ and 1.1×KDP for La_0.3Ce₉（IO₃）₃₆ under 1064 nm laser irradiation,and they are phase matching.It is found that the change of intermediate valence has little effect on the microscopic dipole polarization for these crystals,but has great effect on their linear optical absorption,which further affects SHG efficiency in the range of visible light.Secondly,the first niobium oxy-iodate sulfate compound,Nb₂O₃（IO₃）₂（SO₄）was synthesized through the classical-inorganic-chemical reactions for niobium oxy-sulfate and the strategy of mixed anions.It exhibits wide transparency window（0.38–8μm）,a large phase-matching SHG effect（6×KDP）and high laser damage threshold（LDT）（20×Ag Ga S₂）.Furthermore,it is stable up to 580°C in air,and is stable in water and even in concentrated H₂SO₄.All tests proved Nb₂O₃（IO₃）₂（SO₄）is a potential NLO material.The results of static dipole moment and theoretical calculation showed that SHG effect of Nb₂O₃（IO₃）₂（SO₄）is mainly derived from the Nb O₆ octahedron rather than IO₃^-and SO₄^2-anionic groups.