【作者】 韩树娟；

【导师】 王继扬； 张怀金； 李静；

【作者基本信息】 山东大学 ， 材料学， 2012， 博士

【摘要】 作为二十世纪最重要的发明之一,激光的应用范围覆盖了科研、工业、通讯、医疗、军事以及娱乐等众多领域。然而,激光技术的发展在很大程度上得益于新型激光材料的问世和应用,可以说材料的发展对激光技术的进步起着举足轻重的作用,尤其是新的激光晶体材料的发现。如今,随着激光技术的发展和应用,人们对激光晶体材料在种类和性能上提出了越来越高的要求。对于钼酸盐激光晶体的研究始于20世纪70年代,主要集中在掺杂钼酸盐Nd: LiRE(MoO4)2(RE=Y, La, Gd)等晶体的受激发射特性方面。后来Y3A15O12(YAG)晶体的广泛研究和成功应用,使钼酸盐激光晶体的研究停滞不前。激光二极管泵浦脉冲固体激光器的广泛应用,使人们又开始关注钼酸盐晶体,主要是由于钼酸盐具有自身高度无序结构等特点。其中,具有类白钨矿结构的双钼酸盐AX(MoO4)2是研究热点,A是碱金属离子(Li, Na),X代表稀土元素(Y, La, Gd等)。到目前为止,有关AX(MoO4)2晶体激光实验内容的报道较少,已经报道的有掺Yb3+的NaLa(MoO4)2和LiGd(MoO4)2晶体,另外,福建物构所通过半导体激光器端面泵浦Nd:KLa(MoO4)2晶体首次获得了302mW的1061nm激光输出。然而,对于Nd:LiGd(MoO4)2晶体激光实验还未有报道。相对于AX(MoO4)2晶体,属于单斜晶系的四钼酸盐BaGd2(MoO4)4也是研究热点,研究表明,该类型的稀土激活离子掺杂晶体可用于免加工微片激光器的研究。考虑到钼酸盐激光晶体自身的优势,本文研究了不同掺杂浓度LiNdxGd1-x(MoO4)2(x=0.005,0.01,1)和RE：BaGd2(MoO4)4(RE=Er, Nd, Pr)晶体的生长、热学、光谱及激光性能。另外,考虑到硼酸盐化合物在激光晶体材料领域有着重要的应用,本文通过助熔剂法对BaO-Bi2O3-B2O3体系中的新晶体材料进行了探索。本论文的主要工作如下：钼酸盐激光晶体LiNdxGd1-x(MoO4)2(x=0.005,0.01,1)和RE:BaGd2(MoO4)4(RE=Er, Nd, Pr)的生长及基本物理性质表征采用熔体提拉法生长了不同掺杂浓度的LiNdxGd1-x(Mo04)2(x=0.005,0.01,1)和RE:BaGd2(MoO4)4(RE=Er, Nd, Pr)晶体,讨论了影响晶体质量的因素和提高晶体质量的措施,主要包括选择优质的籽晶、温场的设计、生长工艺参数的调整等。其中,使用优质的籽晶是生长高质量晶体的保证；优质多晶料的合成以及合适温场的建立是生长高质量单晶的前提；控制合适的生长工艺参数是关键。利用X射线粉末衍射(XRPD)的方法表征了所生长晶体的结构,确定了所生长的晶体LiNdxGd1-x(MoO4)2均属于四方晶系,RE:BaGd2(MoO4)4(RE=Er, Nd,Pr)晶体均属于单斜晶系。利用DICVOL软件及粉末衍射数据,计算了所生长晶体的晶胞参数,LiNdxGd1-x(MoO4)2的晶胞参数随着Nd3+离子掺杂浓度的增加而增大；采用“浮力法”测量了晶体在常温下的密度；LiNdxGd1-x(MoO4)2系列晶体的维氏显微硬度测试结果表明,a面的硬度要明显大于c面的硬度,它们的莫氏硬度大约在5.0左右；采用化学腐蚀法对Nd:LiGd(MoO4)2和Er:BaGd2(MoO4)4晶体的品质进行了表征,结果表明,晶体微观缺陷主要是位错和晶界。通过X射线荧光光谱法,确定了晶体中激活离子的分凝系数,对于LiNdxGd1-x(MoO4)2(x=0.005,0.01,1)晶体,随着掺杂Nd3+离子浓度的增大,Nd3+离子在晶体中的分凝系数也变大。相对于Nd3+和Pr3+, Er3+更容易掺入到BaGd2(MoO4)4的晶格中。二、LiNdxGd1-x(MoO4)2(x=0.005,0.01)和RE:BaGd2(MoO4)4(RE=Er, Nd, Pr)的热学性质系统地测量了LiNdxGd1-x(MoO4)2(x=0.005,0.01,1)晶体的热学性质,包括晶体的比热、热膨胀、热扩散系数和热导率等,分析了这些性质随温度及Nd3+掺杂浓度的变化,并讨论了这些性质对晶体生长和应用的影响。利用差热扫描量热计测量了LiNdxGd1-x(MoO4)2(x=0.005,0.01,1)和RE: BaGd2(MoO4)4(RE=Er, Nd, Pr)晶体的比热。对于LiNdxGd1-x(MoO4)2(x=0.005,0.01,1)晶体,随着Nd3+离子掺杂浓度的增大,LiNdxGd1-x(MoO4)2晶体的比热随之变大。在50℃时,x=0.005,0.01,1的LiNdxGd1-x(MoO4)2晶体的比热分别为：0.476,0.504,0.538J·g-1·K-1,通过与其它激光晶体对比,测试结果表明,所生长的LiNdxGd1-x(MoO4)2晶体会有较高的抗光伤阈值。室温下,掺杂Er3+, Nd3+, Pr3+离子的BaGd2(MoO4)4晶体的比热分别为：0.471,0.454和0.395J·g-1·K-1。利用热膨胀仪测量了x=0.005,0.01,1LiNdxGd1-x(MoO4)2晶体在25～500℃左右的热膨胀。在测量的温度范围内,LiNdxGd1-x(MoO4)2晶体a和c两个方向的热膨胀系数均随温度升高而增大。该系列晶体的热膨胀率具有明显的各向异性,c方向的热膨胀率比a方向的热膨胀率大的多,而且这两个方向的热膨胀率差值随温度升高而增大。利用激光脉冲法测量了x=0.005,0.01,1的LiNdxGd1-x(MoO4)2晶体在25～600℃左右的热扩散系数,测试结果显示,c方向的热扩散系数大于a向。室温下,x=0.005,0.01,1的LiNdxGd1-x(MoO4)2晶体a方向热扩散系数分别为：0.504,0.426,0.117mm2·S-1；c方向的热扩散系数分别为：0.518,0.448,0.448mm2·s-1,可以预测,低掺杂量的LiNdxGd1-x(MoO4)2晶体的热稳定性优于高掺杂浓度的晶体。利用热导率与热扩散系数关系的公式计算了x=0.005,0.01,1的LiNdxGd1-x(MoO4)2晶体的热导率,LiNdxGd1-x(MoO4)2晶体c方向热导率高于a方向热导率；a和c两个方向的热导率随温度升高有增大的趋势,可能是由晶体的无序结构引起的。室温下,x=0.005,0.01,1的LiNdxGd1-x(MoO4)2晶体a方向热导率分别为：1.123、1.134和0.314W·m-1·K-1, c方向热导率分别为：1.204、1.193和1.202W·m-1·K-1。三, LiNdxGd1-x(MoO4)2(x=0.005,0.01,1)和RE:BaGd2(Mo04)4(RE=Er, Nd,Pr)的光学性质测量了LiNdxGd1-x(MoO4)2的光学性质,包括晶体的折射率、偏振吸收光谱和荧光光谱。采用棱镜最小偏向角法测量了LiNd(MoO4)2晶体的折射率,得出LiNd(MoO4)2晶体的折射率随着光波波长的增大而减小,且no>ne,晶体为负单轴晶。采用JASCO V570型UV/VIS/NIR分光光度计测量了LiNdxGd1-x(MoO4)2晶体在400～1200nm波段范围内的偏振吸收光谱,结果表明,晶体σ偏振吸收峰的位置比π偏振吸收峰的位置略微红移,并且π偏振吸收比σ偏振吸收强；以氙灯为泵浦源测量了LiNdxGd1-x(MoO4)2晶体在1000～1500nm波段范围内的荧光光谱,并结合Judd-Ofelt理论计算了晶体吸收和发射的光谱参数。结果表明,掺杂浓度为0.5at.%和1at.%的Nd:LiGd(MoO4)2晶体的光谱参数差异不大；晶体在1061nm附近的发射强度最强,是最容易实现激光输出的谱线,计算了它们在1061nm处的发射截面分别为：18.76×10-20cm2和20.04×10-20cm2。Er:BaGd2(MoO4)4晶体在1536nm波长的发射截面为4.50×10-20cm2,有利于该晶体在1536nm处实现人眼安全的激光输出；Nd:BaGd2(MoO4)4晶体1060nm处的发射截面为24.68×10-20cm2; Pr:BaGd2(MoO4)4晶体在651nm处的发射截面为1.7930×10-18cm2,有利于红光的输出。四、LiNdxGd1-x(MoO4)2(x=0.005,0.01,1)晶体激光性能的研究以中心发射波长为808nm的光纤耦合的半导体激光器作泵浦源,对LiNdxGd1-x(MoO4)2(x=0.005,0.01,1)晶体进行了1060nm连续激光实验。这是首次报道的Nd:LiGd(MoO4)2晶体的连续激光实验。结果发现,LiNd(MoO4)2晶体没有出光,主要是由于该晶体严重的浓度猝灭效应造成的；从掺杂浓度分别为0.5at.%和1at.%的Nd:LiGd(MoO4)2晶体中得到了激光输出,发现c切的激光输出功率比a切的低,并且阈值较大,a切晶体的激光输出波长为1060.6nm,c切晶体的激光输出波长为1067.8nm,其中a切3mm×3mm×10mm的1at.%掺杂的Nd:LiGd(MoO4)2晶体的实验结果最好,其泵浦阈值为0.276W,当入射泵浦功率为7.77W时,其最大输出功率为920mW,相应的光光转换效率为11.84%。五、BaO-Bi2O3-B2O3体系晶体助熔剂生长探索采用助熔剂法对BaO-Bi2O3-B2O3体系中的BaBiBO4晶体进行了探索。实验表明,在B2O3、Bi2O3、BaO以及它们之间作用形成的化合物等自助熔体系中,我们没有得到任何晶体；在以Li2Mo3O10为助熔剂时,通过自发成核和顶部籽晶法分别得到BaMoO4多晶和LiBaB9O15单晶。这是由于原料中H3BO3和Bi2O3密度相差太大,另外H3BO3容易挥发,从而导致熔体分层,难以获得均匀熔体,最终造成在熔体底部和顶部得到的晶体不同。对于得到的LiBaB9O15晶体,我们从中选择较好的晶粒作为籽晶,通过顶部籽晶法生长了大单晶,并对其进行了研究。采用单晶X-射线衍射获得了晶体的结构,其空间群为R3c,晶胞参数为a=b=10.9679A, c=17.0457A, V=1775.79A3.利用高分辨X射线衍射和化学腐蚀法对晶体的品质进行了表征,结果表明所生长的晶体内部缺陷主要是位错。采用热膨胀仪测量了LiBaB9O15晶体在25～500℃左右的热膨胀程度,结果表明,在测量的温度范围内,晶体存在各向异性,随温度升高,a方向发生热膨胀,而c方向发生热收缩,但是膨胀的总体效果是其单胞体积略微变大,通过公式计算了该晶体的平均线性热膨胀系数αa=6.56×10-6K-1,αc,=-4.82×10-6K-1,晶体热膨胀的各向异性与其结构有关。另外,我们还利用激光脉冲法测量了LiBaB9O15晶体在20-400℃左右的热扩散系数并通过公式计算了热导率的大小,结果表明,LiBaB9O15晶体a和c两个方向的热扩散系数和热导率各向异性比较明显,均随温度的升高而减小,在20℃时,a、c方向的热扩散系数分别是0.991mm2·s-1和2.977mm2·s-1,热导率分别是1.825W·m-1·K-1和5.132W·m-·k1。采用Hitachi U-3500型IR-VIS-UV分光光度计和NEXUS670FTIR红外光谱仪,分别测量了LiBaB9O15晶体(100)和(001)晶面在120-2200nm和2200-3200nm范围的透过率,结果显示,LiBaB9O15晶体的紫外透过截止边在165nm左右,晶体200-2200nm的透过率保持在90%左右。采用棱镜最小偏向角法测试了该晶体从250到2400nm中13个波长处的折射率。可以看出晶体的常光折射率n0大于其非常光折射率ne,因此晶体属于负单轴晶。更多还原

【Abstract】 As one of the most important innovations of the twentieth century, laser has been widely used in the fields of science, industry, communication, medical treatment, military and amusement. However, the advent and applications of laser materials, especially the laser crystals, have been played a vital role in the development of laser technique. Nowadays, with the development and applications of laser, high level demands are put forward on the characters and performance of the laser crystals.Molybdate laser crystals were investigated during1970’s, the research was focused on stimulated emission characteristics of LiRE(MoO4)2(RE=Y, La, Gd) crystals. As the thoughtful investigations and successfully applications for Y3Al5O12(YAG) crystals, the research interest was transferred to YAG from molybdate laser crystals. Along with the widely applications of laser diode pumped solid state lasers, re-evaluation of the molybdate crystals has garnered a tremendous amount of attention because of its highly disordered structure. Alkali metal-rare earth-double molybdate crystals with the formula AX(MoO4)2(A=Li, Na; X=Y, La, Gd) have been investigated as laser gain hosts. Up to now, there were few report on the laser experiment of AX(MoO4)2-Laser properties of Yb3+-doped NaLa(MoO4)2and LiGd(MoO4)2crystals have been reported. The laser output was302mW from Nd3+KLa(MoO4)2crystal pumped with a diode laser. However, there is no report on laser properties of Nd:LiGd(MoO4)2crystals. Compared to AX(MoO4)2crystals, AX2(MoO4)4(A=Ba; X=Gd), belonging to monoclinic crystal system, have been also attracted many attentions. The results suggested that the rare-earth doped AX2(MoO4)4crystals might be regarded as a potential free processing microchip laser material for diode laser pumping. Considering the advantage of molybdate crystals, growth, thermal properties, optical spectra and laser performace of LiNdxGd1-x(MoO4)2(x=0.005,0.01,1) and RE:BaGd2(MoO4)4(RE=Er, Nd, Pr) have been investigated in this work. In addition, considering the important applications of borate laser crystals, exploration of new crystal from the BaO-Bi2O3-B2O3system has also been investigated in this work. The research work of the thesis can be overviewed as follows:Ⅰ. Growth and physical properties characterizations of LiNdxGd1-x(MoO4)2(x=0.005,0.01,1) and RE:BaGd2(MoO4)4(RE=Er, Nd, Pr) crystalsLiNdxGd1-x(MoO4)2crystals with different Nd3+concentrations and RE: BaGd2(MoO4)4(RE=Er, Nd, Pr) crystals have been grown by the Czochralski method. The main factors that influence the crystal growth and quality have been discussed. The high quality seed is very important to improve the crystal quality. The synthesis of high quality polycrystalline material and design of reasonable temperature field are the precondition for the growth of single crystal. In addition, controlling appropriate parameters is the key to crystal growth.The structures of the as-grown crystals were determined by X-ray powder diffraction. The results confirm that the as-grown crystals LiNdxGd1-x(MoO4)2belong to the tetragonal crystal system and RE:BaGd2(MoO4)4(RE=Er, Nd, Pr) belong to monoclinic crystal system. The lattice constants of these crystals were calculated by the DICVOL programme. The lattice constants of LiNdxGd1-x(MoO4)2increase with the increasment of x. The density of the as-grown crystal was measured by the buoyancy method. The results of the Vickers microhardness measurement showed that the microhardness of a-cut wafer is larger than that of c-cut wafer. The Mohs’ hardness value is on the order of5.0. The microdefects of Nd:LiGd(MoO4)2crystal were observed by chemical etching method. The result showed that the main defect of the crystal were dislocation and grain boundaries. For LiNdxGd1-x(MoO4)2crystals, the segregation coefficient of Nd3+increase with increasing doping concentration. Compared with Nd3+and Pr3+ions, Er3+ion is easier to be doped into the lattice of BaGd2(MoO4)4.Ⅱ. Thermal properties of LiNdxGd1-x(MoO4)2(x=0.005,0.01,1) and RE: BaGd2(MoO4)4(RE=Er, Nd, Pr) crystalsThe thermal properties of the LiNdxGd1-x(MoO4)2(x=0.005,0.01,1) single crystals were investigated systematically, including specific heat, thermal expansion, thermal diffusion coefficients and thermal conductivity. These properties on the function of temperature and Nd3+doped concentration were analysed. The influence of these properties on crystal growth and applications were also discussed.The specific heats of LiNdxGd1-x(MoO4)2(x=0.005,0.01,1) and RE: BaGd2(MoO4)4(RE=Er, Nd, Pr) crystals were measured by differential thermal scanning calorimeter. For LiNdxGd1-x(MoO4)2, the specific heat increases with increasing x value. At50℃, specific heats of x=0.005,0.01,1LiNdxGd1-x(MoO4)2are0.476,0.504,0.538J·g-1·K-1, respectively. The result shows that these crystals may have higher resistance to laser damage. At room temperature, the specific heats of Er3+, Nd3+, Pr3+doped BaGd2(MoO4)4crystal are:0.471,0.454,0.395J·g-1·K-1, respectively.The thermal expansions of LiNdxGd1-x(MoO4)2with x=0.005,0.01,1were measured by thermodilatometer in the temperature range of25-500℃. The values of thermal expansion along c axis are larger than that of a axis from the experimental results and this shows that the crystals exhibit an anisotropic thermal expansion. Difference of the thermal expansion coefficients between the two directions increases with the increasing temperature.The thermal diffusion coefficients of LiNdxGd1-x(MoO4)2with x=0.005,0.01,1in the temperature range of25-600℃were measured by the laser flash method. The values of thermal diffusion coefficients along c axis are larger than that of a axis, and the principal thermal diffusion coefficients of LiNdxGd1-x(MoO4)2with x=0.005,0.01and1at room temperature are λ1=0.504,0.426,0.117mm2·s-1and λ3=0.518,0.448,0.448mm2·s-1.The thermal conductivity of LiNdxGd1-x(MoO4)2was calculated. The results show that the thermal conductivity increases with the increasing temperature, which is attributed to the disordered structure. At room temperature, the thermal conductivity of LiNdxGd1-x(MoO4)2with x=0.005,0.01,1are κ1=1.123,1.134,0.314W·m-1·K-1and κ3=1.204,1.193,1.202W·m-1·K-1.Ⅲ. Optical properties of LiNdxGd1-x(MoO4)2(x=0.005,0.01,1) crystalsThe refractive index, polarization absorption spectrum and fluorescence spectrum of LiNdxGd1-x(MoO4)2crystals were measured. The refractive indice of LiNd(MoO4)2was measured by the minimum deviation method. The result showed that the refractive index of LiNd(MoO4)2is decreasing with the increasing of the wavelength. The smaller difference between the refractive indices values of no and ne indicated that the crystal is an optically uniaxial negative crystal.The polarized absorption spectra were measured for LiNdxGd1-x(MoO4)2in the wavelength range of400-1200nm. The result showed that the absorption peaks for σ-polarization had slightly red shif than that of π-polarization. Upon excitation of the LiNdxGd1-x(MoO4)2at806nm, the luminescence emission spectrum was measured. Based on these spectra and J-O theory, the optical spectral parameters of LiNdxGd1-x(MoO4)2have been calculated. The results show that the difference among the parameters of LiNdxGd1-x(MoO4)2(x=0.005,0.01) is insignificant. The strongest emission is located near1061nm and it is easy to obtain laser output. For LiNdxGd1-x(MoO4)2(x=0.005,0.01), the emission cross-sections at1061nm are18.76×10-20cm2and20.04×10-20cm2.The emission cross-section at1536nm for Er:BaGd2(MoO4)4is4.50×10-20cm2, which is advantageous for generation of laser operation. The emission cross-section at1060nm for Nd:BaGd2(MoO4)4is24.68×10-20cm2.The emission cross-sections at651nm for Pr:BaGd2(MoO4)4is1.793×10-18cm, which is beneficial for generation of red laser.Ⅳ. Laser performance of LiNdxGd1-x(MoO4)2(x=0.005,0.01,1) crystalsThe continuous-wave (CW) laser experiments of LiNdxGd1-x(MoO4)2crystals operating at1060nm were carried out by using a LD pump source centered at808nm. This is the first time for reporting the CW laser output of Nd:LiGd(MoO4)2crystals. It has been found that there is no laser output from LiNd(MoO4)2due to the concentration quenching effect of the crystal. For0.5at.%and1at.%doped Nd: LiGd(MoO4)2crystals, the laser output power of c-cut was lower than that of a-cut. And c-cut crystal had a higher pump threshold.A-cut sample with the size of3mmx3mmx10mm of1at.%doped Nd:LiGd(MoO4)2crystal had the best laser output power. Its pump threshold is0.276W, the maximum output power is920mW and the optical conversion efficiency is11.84%.Ⅴ. Exploration of new crystal from BaO-Bi2O3-B2O3system by the flux methodSelf-flux systems, such as B2O3, Bi2O3, BaO, for growing BaBiBO4were explored. The results showed that it is difficult to obtain BaBiBO4crystal from self-flux systems. Due to the density difference of B2O3and Bi2O3and the volatile of B2O3, it is difficult to obtain homogeneous melt. Using a Li2Mo3O10flux system, two different phase crystals, BaMoO4polycrystal and single crystal LiBaB9O15, were obtained by the spontaneous nucleation and top-seeded growth method.A large LiBaB9O15single crystal has been grown by top-seeded solution growth method using a Li2Mo3O10flux system. The structure of LiBaB9O15crystal was obtained by single crystal X-ray diffraction. The compound crystallized in the trigonal system. The crystal cell parameters are a=b=10.9679A, c=17.0457A, V=1775.79A3. The crystal quality was characterized by high-resolution X ray diffraction and chemical etching method. The results show that the crystal obtained is of excellent quality and the main defect is dislocation.The thermal expansion was measured by thermodilatometer in the temperature range of25～500℃. The results show that the crystal has an anisotropic thermal expansion. The material exhibits a positive thermal expansion along the a-axis, which is coupled with negative thermal expansion along the c-axis over the measured temperature range from25to500℃. The average thermal expansion coefficients are αa=6.56×10-6K-1, αc=-4.82×10-6K-1. The combination of the positive and negative thermal expansion of this crystal leads to a small net volume expansion. The thermal diffusion coefficient in the temperature range of25～600℃was measured by the laser flash method. The results show that thermal diffusion coefficients along c axis are much larger than that of a axis, and the principal thermal diffusion coefficients at room temperature are λ1=0.991mm2·s-1and λ2=2.977mm2·s-1. The thermal conductivity was calculated, and it was decreased with the increasing temperature. At room temperature, its principal thermal conductivities are:κ1=1.825W·m-1·K-1and κ2=5.132W·m-1·K-1.The transmittance spectrum was measured at room temperature using a Hitachi U-3500spectrophotometer and a NEXUS670FTIR Spectrophotometer over the ranges of120-2200nm and2200-3200nm. The deep-UV transparency cutoff wavelength of the as-grown crystal occurs at165nm. The transmittance over the wavelength range of165-200nm increases sharply from0to above90%and remains at about90%over the wavelength range of200-2200nm. The ordinary and extraordinary refractive indices n0and ne, of the LiBaB9O15crystal were measured at room temperature by the minimum deviation method at13different wavelengths from250to2400nm. LiBaB9O15is confirmed to be a negative uniaxial optical crystal.更多还原