Preparation Of Ⅰ-Ⅲ-Ⅳ-Se(Ⅰ=K,Cs;Ⅲ=Ga,In;Ⅳ =Si,Ge,Sn) Selenide And Their Applications In Infrared High Power Laser Technology

As one type of important photoelectric information functional materials,nonlinear optical(NLO)crystals are one of the core components for laser device,which are widely used in laser weapons,laser processing,laser communication,medical instruments,and so on.So the design and development of new NLO crystal materials have become a hot topic in this field.Currently commercial infrared NLO crystal materials mainly include AgGaS2(AGS),AgGaSe2(AGSe),and ZnGeP2(ZGP).They have the advantages of large nonlinear coefficients and wide infrared transparent windows,but they also have intrinsic disadvantages such as low laser-induced damage thresholds(LIDTs)and harmful two-photon absorption,which limit their applications.So,it is urgent to find infrared NLO crystals with good performance to relieve the pressure on them.Therefore,designing reasonable and effective synthesis strategies is conducive to exploring new infrared NLO crystalline materials with ideal properties.One of the difficulties in designing NLO crystals is to constructe noncentrosymmetric(NCS)structures,so the topic of this thesis puts forward three novel design strategies to address this issue.Firstly,the disorder caused by partial congener substitution induces symmetry breaking,thus the centrosymmetric(CS)structures transform to NCS ones.From the perspective of the NLO material’ structural requirements,crystallizing in a NCS structure is the essential requirement for its NLO activity.Secondly,the three lattice positions in the structure are randomly co-occupied by multiple elements.From the perspective of structure-property relationship,the combination of different acentric functional motifs is likely to increase the possibility to discover new structures and obtain crystal materials with excellent performance.Finally,one lattice position in the crystall structure is randomly co-occupied by multiple elements.From the perspective of comprehensive performance,it is beneficial to introduce functional motifs which can increase the NLO activity into simple and stable structure with low thermal expansion coefficient(TEA),so as to achieve the balance between large second harmonic generation(SHG)effect and high LIDT.According to these design strategies,this thesis finally obtains several promising infrared NLO crystal materials with excellent performance,and we study their NLO properties systematically.The specific works are as follows:(1)The strategy of partial congener cationic substitution to create symmetric breaking to design and synthesize selenides with NCS structures is proposed.Two new pentanary metal selenides,K3Ga3(Ge6.17Sn0.83)Se2O(1)and K3Ga3(Ge4.95Si2.05)Se20(2),were synthesized by a high temperature solid state method.They crystallize in the monoclinic NCS space group Pc,different from the monoclinic CS space group P21/c of the parent compound K3Ga3Ge7Se20.Their structures feature three-dim ensional(3D)｛[Ga3(Ge7-xMx)Se2O]3-}∞(M=Si,Sn)polyanionic framework built from the basic functional motif M’Se4(M’=Ga,Ge,M)tetrahedra,similar but a little different from that of K3Ga3Ge7Se20.Their NCS structures are verified by the NLO activities.The SHG response of 1 is～1/3 times that of benchmark AgGaS2 under a 2.1μm laser radiation,while 2 exhibits a weak effect,and both of them are NLO phase-matchable.From the comparison of the NLO activities of 1 and 2,it can be seen that the introduction of heavy atoms can increase the SHG effect.Their optical band gaps are measured to be 2.02 and 2.12 eV,and they are transparent in the range of 0.61-25 and 0.58-25μm,respectively.In addition,TB-LMTO-ASA calculation addressing electronic structure are performed,and the reason ability of 3 Ga:7 Ge in 1 and 2 is well verified by calculation results(2)A str ategy is proposed by the three lattice positions in the crystal structure randomly co-occupied by multiple elements to design and synthesize NCS selenides.A novel pentanary selenides,KInSi1.32Sn0.68Se6),was synthesized by a high temperature solid state reaction.It crystallizes in the monoclinic NCS space group Cc,featuring a 3D[(InSi1.32Sn0.68Se6)-]n polyanionic network,and its powder sample presents promisin g NLO behaviors,viz.1.3 times SHG response and close LIDT than those of benchmark AGS.Besides,it is phase-matchable and shows a wide transparent region.Theoretical calculation addressing its electronic structure and optical property are also performed(3)A three-in-one strategy is proposed by the one lattice position in the crystal structure are randomly co-occupied by multiple elements to design and synthesize selenides with NCS structures.A series of pentanary infrared NLO materials CsMⅢMⅣSnSe6(MⅢ＝Ga,In;MⅣ=Si,Ge)were synthesized by high temperature solid state reactions,viz.three kinds of elements(MⅢ,MⅣ,and Sn)in one position.Their 3D structures are constructed by the MQ4(M denotes MⅢ,MⅣ,an d Sn)tetrahedral un its.They exhibit promisin g hybrid NLO properties,witnessed by their moderate/large SHG effects of 0.52,0.98,1.05,and 1.12 times that of benchmark AGS,and high powder LIDT values of 6.9,4.1,8.1,and 5.4 times that of AGS,respectively.The TEA is less than the benchmark AGS,which well explains the cause of high LIDT.These results prove that they have good comprehensive NLO performance.These NLO properties are well verified by Density Functional Theory calculation results.The three-in-one strategy of designing high-performance infrared NLO materials will extended to more field,which is of guiding significance for the further design and synthesis of infrared NLO chalcogenides.