Study On Mercury Halides As New Mid-infrared Nonlinear Optical Materials

Nonlinear optical（NLO）crystal materials are key materials for high technology,and have played very important role in the field of laser technology.At present,the current commercial mid-Infrared（mid-IR）NLO materials are heavily hindered owing to their low laser damage threshold（LDT）.The aim of the work is to explore new type of mid-IR NLO materials with high LDT.This dissertation focuses on mercury halides,due to the following considerations,1)Mercury halides contain heavy metal,so as to exhibit a wide window of infrared region;2)Mercury halides are insulators so as to improve the band gap and laser damage thresholds;3)Mercury halides have relatively good stability in physical and chemical properties.There are four chapters in this dissertation,the contents and creative work are as follows,In Chapter One,some basic knowledge of NLO crystal materials is mainly introduced,and the latest research progress of second-order NLO crystal materials in the IR region are reviewed briefly.The main idea and contents of this thesis are then provided based on these.In Chapter Two,according to the benefits and shortcomings of RbCdI₃.H₂O,i.e,RbCd I₃.H₂O may exhibit strong phase-matchable powder second harmonic generation effect and has lower band gap,while the crystal water may restrict its application.So we choose mercury as central element,while RbI and HgI₂ as starting materials,then a new ternary halide RbHgI₃ was successfully synthesized by the solution reaction method.RbHgI₃ shows strong phase-matchable SHG response of about 14 times that of KH₂PO₄（KDP）.The transparent range of the powders is wide（0.484⁷9 μm）and the thermal stability is relatively high（close to 110 ℃）,and the band gap is 2.56 eV,and the laser damage threshold is 28.3 MW/cm².Based on these behaviors,the compound RbHgI₃ may be a potential candidate for nonlinear optical material used in the mid-IR region.In Chapter Three,a new phase of HgBr₂ was synthesized by substitution reaction in EtOH solution.We named this new crystal β-HgBr₂ to discriminate the common α-HgBr₂.Its crystal structure is confirmed by single crystal X-ray diffraction.Its NLO property and some other related properties are measured.β-HgBr₂ shows strong phase-matchable SHG response of about 9 times that of KH₂PO₄（KDP）.Its laser damage threshold is approximately 290 MW/cm²,which is nearly 10 times as that of the commercial Ag₂GaS₂.The transparent range of the powders is wide（0.38³2.3μm）.And the thermal decomposition temperature is about 110 ℃.In a word,β-HgBr₂ is an excellent nonlinear optical material in the mid-IR region.In Chapter Four,KHgI₃·H₂O was synthesized by KHgBr₃·H₂O pattern.KHgI₃·H₂O is a known substance,but its NLO property has not been reported before.To discuss the relationship between the structure and the performance of KHgI₃·H₂O,its structure was confirmed by single crystal X-ray diffraction.KHgI₃·H₂O shows strong phase-matchable SHG response of about 6 times that of KH₂PO₄（KDP）.The transparent range of the powders is wide（0.48 2.7、2.9 6、6.5 100 μm）by FT-IR,UV-Vis and Raman spectrum measurement.And the thermal decomposition is about 100 ℃.All overall performance shows that KHgI₃·H₂O is a potential nonlinear optical material.