【作者】 方奇术；

【导师】 陈红兵；

【作者基本信息】 宁波大学 ， 无机化学， 2010， 硕士

【摘要】 近二三十年来,LiCaAlF₆晶体作为优良的可调谐激光晶体基质材料,受到国内外学者的广泛关注。至今, Ce³⁺:LiCaAlF₆晶体作为紫外可调谐晶体的晶体生长和光谱性质已被大量文献报道,证实Ce³⁺:LiCaAlF₆晶体在可调谐激光领域有着重要用途。与此同时LiCaAlF₆掺杂其它过渡或稀土离子的发光特性及闪烁、激光性能正在被越来越多研究机构探索和报道。另外一方面,优质大尺寸的LiCaAlF₆单晶具有深紫外可见高透过率、双折射效应较小,且物化性质稳定,不易潮解,在紫外窗口材料领域有着重要应用前景。但LiCaAlF₆晶体及Ce³⁺:LiCaAlF₆晶体生长技术固有难点,限制该类晶体产业实用化。该类晶体生长主要难点在于:（1）获取严格无水无氧的单一相LiCaAlF₆及Ce³⁺:LiCaAlF₆多晶料十分困难;（2）如何控制LiCaAlF₆及Ce³⁺:LiCaAlF₆晶体生长气氛,防止晶体氧化及组分挥发;（3）晶体各向热膨胀系数相差较大,生长过程中易形成缺陷甚至开裂。本论文采取非真空密闭坩埚下降法进行LiCaAlF₆及Ce³⁺:LiCaAlF₆晶体生长,通过设计和改进实验条件,探索出适合该单晶生长条件,获得了透明单晶,就该晶体材料的光学性能进行了测试表征。本论文主要获得了以下结果:（1）成功探索出合成严格无水无氧单一相的LiCaAlF₆及Ce³⁺:LiCaAlF₆多晶料的工艺。该工艺以高纯氟化物为初始原料,严格按照化学式的计量比配料,并充分混合原料。在高纯HF气氛保护下,对原料在程序控温条件下进行氟化烧结处理,合成出晶体生长所必需的无水无氧LiCaAlF₆及Ce³⁺:LiCaAlF₆多晶料。（2）优质LiCaAlF₆及Ce³⁺:LiCaAlF₆晶体的非真空密封坩埚下降法生长工艺。采用无水无氧LiCaAlF₆及Ce³⁺:LiCaAlF₆多晶料,致密填充在特制坩埚中,而后加入少量聚四氟乙稀粉末,进行晶体坩埚下降法生长。生长参数为:炉体温度调节于910～930oC,固液界面温度梯度30oC/cm左右,坩埚下降速率控制于0.5¹.0 mm/h,晶体生长完成后以20～50℃/h的速率缓慢降低炉体温度。成功生长无宏观缺陷的LiCaAlF₆及Ce³⁺:LiCaAlF₆晶体样品。（3）LiCaAlF₆及Ce³⁺:LiCaAlF₆单晶的表征。应用XRD、紫外—可见透射光谱、红外光谱分别对生长加工后的LiCaAlF₆及Ce³⁺:LiCaAlF₆单晶光谱性质进行表征。测试表明,LiCaAlF₆单晶吸收截止线位于深紫外区,在紫外可见光区透过率达85%以上,同时红外光谱显示,该单晶无OH-吸收带,从而证实坩埚下降法生长LiCaAlF₆单晶性能良好。Ce³⁺:LiCaAlF₆单晶表征表明266nm左右,有宽带特征吸收峰Ce³⁺宽带特征吸收峰,其红外光谱出OH-微弱吸收峰,在257,267nm波长光激发下,均可获得在290nm和310nm存在两个宽带发射峰。（4）LiCaAlF₆及Ce³⁺:LiCaAlF₆单晶的生长及加工工艺的改进。为降低晶体生长成品率及提高晶体生长效率,通过一炉多管或一管多坩埚进行垂直坩埚下降法生长,获得较好的晶体生长结果,为产业化批量LiCaAlF₆及Ce³⁺:LiCaAlF₆单晶生长提供实验基础。通过对晶体性能研究和晶体加工实践总结,得出适合该类单晶加工工艺。更多还原

【Abstract】 LiCAF as a tunable laser host has been aroused much attention from scholars in the past decades. Up to the presest, UV spectrum properties and gowth method of Ce:LiCAF has been widely reported by literatures, which prove Ce:LiCAF has potential use in all-solid LD pumped UV laser. At the same time, luminescence and scintilla property of LiCAF doped transition or rare earth ion is investigating by more and rmore institutions. So far, doped LiCAFcrystals have attracted a lot of attentions as potential material for optical components in VUV, fast scintillators, thermoluminescent dosimeters and laser hosts. On the other hand, pure LiCAF crystal has many advantages as primary candidates UV window materials, because of its’unique properties, such as a large band gap, small birefringence, stabilization and high UV/VI transparency. However, many difficulties exist in crystal growth of pure and doped LiCAF, limiting the utility of these crystals. First, it lacks effective technologic method to obtain the rigorous anhydrous LiCAF and Ce:LiCAF polycrystalline material. Second, diffculty of safe gas handling is used to Controlling the growth atmosphere to avoid the melt oxygenation and volatilization in the process. Last, There is a notable di?erence in the linear thermal expansion coe?cient along the a-axis and along the c-axis of LiCAF and Ce:LiCAF crystals. It suggests that large diameter LiCAF and Ce:LiCAF crystals are dicult to grow from the melt because of thermal stress inside the grown crystals. The growth of LiCAF and Ce:LiCAF single crystals by modified Bridgman process in nonvacuum atmosphere is described in the present work. According to exploring the optimal growth conditions, High optical performances characterized by transmission spectrum and fluorescence spectrum.are achieved using crystals grown in this way. The primary outcomes are as follows:(1) The successful method synthesizing the rigorous anhydrous LiCAF and Ce:LiCAF polycrystalline material is described by the work. Using high purity fluoride as initial agents, the raw material is mixed according to stoichiometric ratio. Under the HF atmospheresafe as safe gas, the anhydrous material is obtained by sintering according to the unique fluoration technology.(2) Describing the method of growth of high performances LiCAF and Ce:LiCAF single crystals by the modified Bridgman growth under nonvacuum atmosphere. Filling the double shells platinum crucibles with the polycrystalline material, a little of polyterafluoroethylene power is added to the crucibles to exhaust the oxygen sealed in the crucibles. Growth parameters as follow: The furnace temperature is controlled at 910～930oC, the temperature gradient across solid-liquid interface is adjusted at about 30oC/cm with the lowering rate in the range of 0.5~1.0 mm/h and the furnace temperature lowering rate keeping at 20～50℃/ h. The transparent crystals are obtained from the crucibles.(3) As-grown LiCAF and Ce:LiCAF crystals are characterized by XRD, UV/VI transmission spectrum and fluorescence spectrum. The results suggest that LiCAF and Ce:LiCAF single crystals have high transparent optical properties during the UV/VI range, with Ce:LiCAF crystals have unique absorption band around the 260nm . No evident OH- absorption is observed in IRspectrum. Under the excitateding by 257 or 267nm radiation, the fluoscence spectrum of Ce:LiCAF crystals have two emission broad bands at 290nm and 310nm.(4) Descibeing the modified technology of as-grown crystals growth and processing. To improving the efficiency and reducing the cost of crystal growth, the method increasing the number of refractory tubes in the furnace or the crucibles in the refratory tube is adopted in the work. The outcomes suggest the probability of industrialization of high performances LiCAF and Ce:LiCAF single crystals. According to the analysis of characters of LiCAF and Ce:LiCAF crystals, a modified crystal processing which is same with LiCAF and Ce:LiCAF crystals is summarized.更多还原