| Since the 1960s,nonlinear optical(NLO)crystals with variable frequency function have become important components for outputting laser source.NLO crystals are widely used in second harmonic generation(SHG),optical parametric amplification,optical parametric oscillation(OPO)and so on.According to the applied regions,NLO crystals can be divided into deep ultraviolet,ultraviolet,visible light and near infrared(NIR),middle and far infrared(MFIR)wavelength ranges.Currently,commercially available MFIR crystals are far from meeting market requirements,such as benchmark AgGaQ2(Q=S,Se)and ZnGeP2,whose inherent defects such as two-photon absorption and low laser-induced damage threshold(LIDT)limit their application.Therefore,it is urgent to explore MFIR NLO crystals with excellent performance.Chalcogenides with wide IR windows and large second harmonic effects are important candidates for MFIR NLO crystal materials.In order to obtain better performance ones,the following methods can be adopted:(1)The introduction of alkali metal(A)or alkali-earth metal(AE)into chalcogenides is beneficial to obtain large band gap and high LIDT.(2)It is a common method to inclusion of MQ4(M=Ga,In,Si,Ge,Sn)tetrahedral functional motifs.(3)Based on the symmetry breaking of the existing centrosymmetric(CS)compounds,new non-centrosymmetric(NCS)NLO crystal materials can be obtained.(4)By introducing Ag+or Hg2+ions with d10 electron configuration,NLO crystal materials with large band gaps and large SHG effects are expected.Based on the above considerations,we use K/Ba as the main alkali/alkali-earth metal ions in the reaction,and introduce Ga or In element normally fourfold-coordinated with S,so as to design and synthesize new MFIR NLO crystal materials.Then,we designed to obtain new NLO materials by trying to inclusion of Hg2+ ion with d10 electronic configuration.Specific work contents are as follows:(1)A new ternary sulfide Ba6In2S10 with new structure-type was synthesized by high temperature solid state method.It crystallizes in the hexagonal chiral space group P63.Its structure can be described as isolated InS4 tetrahedra arranged in reverse to form a zerodimensional structure,in which strong ionic Ba2+ions surround the InS4 tetrahedra.In the structure,both In and S atoms are disordered,and the structure contains a typical S-S bond.Ba6In2S10 shows obvious NLO response,and its LIDT is 6.3 times that of AGS.The source of its NLO response is analyzed deeply through the calculation of dipole moment.It has a large band gap(3.72 eV)and a wide infrared transmission range(0.25-25μm).(2)KHg4Ga3S9,a new member of the A-N-M-Q(A=alkali metal;N=Zn,Cd,Hg;M=Ga,In;Q=S,Se)family,crystallizes in the chiral space group C2221 of the orthorhombic system.The three-dimensional {[Hg4Ga3S9]3-}∞ anionic framework of KHg4Ga3S9 is composed of GaS4 and HgS4 tetrahedra,K+ion as counterion.A typical 21 spiral axis exists in the structure.The first type of spiral axis {[HgGa3S13]15-}∞ grows along the a direction,and the second type {[Hg3GaS11]13-}∞ grows along the b direction.The NLO response is 0.4 times that of AGS and the LIDT is 5.0 times of AGS.Its band gap is 3.00 eV and the IR transmission range is 0.25-25 μm.(3)K2Ba7HgIn4S16,a pentanary sulfide with new structural type,was synthesized by high temperature solid state method.It crystallizes with the chiral space group P21212 of the orthorhombic system.The structure is built by {[In2S7]8-}∞ chains and isolated HgS4 planar units surrounded by strong ionic K+and Ba2+ions between the chains.It demonstrates a moderate NLO response,about 0.5 times that of AGS,a high LIDT 5.8 times of AGS,a band gap of 2.86 eV and a wide IR transmittance range(0.25-25μm).It represents the pioneer in the A2AE7NM4Q16(A=alkali metal;AE=alkaline-earth metal;N=Zn,Cd,Hg;M=Ga,In;Q=S,Se)family and is a promising IR NLO material. |
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