【作者】 孙金超；

【导师】 王锐； 徐衍岭；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2014， 博士

【摘要】 Ca12Al14O33是一种拥有特殊笼状结构的透明导电氧化物，如果将笼状结构内部离子进行替换，其结构、光学性能和电学性能也会随之改变。通过氧化还原反应和离子注入等多种方式可以直接或间接的取代笼状结构内部O2-离子形成一系列C12A7材料的衍生物，C12A7的晶格常数也会随着衍生物中取代离子直径和电荷状态的不同而改变。e-、H-、Cl-、OH-和F-等离子都可以成为取代离子，这些离子进入到晶格内部取代氧离子从而形成新的化合物。本文通过提拉法制备C12A7单晶以及Er3+/Yb3+共掺杂C12A7单晶，研究了单晶生长工艺对晶体质量的影响。研究发现烧结工艺、炉内气氛、生长速率和温度场等工艺条件对单晶的质量有很大的影响，其中氧气含量是决定晶体质量的关键因素之一，氧气含量过多会导致坩埚氧化，并使晶体着色同时产生气泡缺陷，氧气含量过少会导致材料分解。这主要是由于在氧气含量过高的条件下，熔体中溶解的氧会在结晶的过程中会形成气泡缺陷，同时坩埚材料也会被氧化而引入铱离子杂质导致晶体开裂。少量的气泡缺陷可以通过退火的手段消除。对工艺参数进行调整，确定了最佳工艺条件：气氛条件是0.5%O2含量的N2气氛，原料为CaCO3和α-Al2O3，坩埚为铱金坩埚，晶体的生长温度为1350℃，提拉速度为1mm/h，旋转速度为25~30rad/min，液面上温度梯度为30℃/cm，退火温度为1300℃，退火温梯度为50℃/h。通过理论分析研究了C12A7内部离子对其光学和电学性能的影响，运用能量最小的优化原则对理论计算条件中截断能、Ｋ点、赝势以及泛函进行选择，确定了截断能为340eV，K点为444，赝势为NCP，泛函为PW91。优化并建立C12A7与C12A7的衍生物模型，分析其结构和光学性能。研究发现C12A7及其衍生物禁带均由框架结构与内部的离子共同构成的，框架结构与自由离子之间形成一种金属键，禁带范围随着内部离子极化能力的增大而增大，并向离子周围移动，同时费米能级位置随着内部离子极化能增大而升高。分别在氧气中氧化和在氢气中还原获得了C12A7的衍生物，通过对结构和光学性能的分析研究材料之间的离子交换过程。结果表明在氧化气氛中C12A7可被氧化成C12A7:O-，在还原气氛中C12A7可被还原成C12A7:H-。通过高温固相法合成了Er3+/Yb3+C12A7稀土掺杂粉末晶体，Er离子含量为1%，Yb离子从0变化到20%，随着掺杂离子含量的变化，其红绿光的发光强度也在增强，上转换红光增加的较多。通过调节掺杂离子Er离子和Yb离子浓度获得最佳发光效果。此时530nm的绿光对应Er3+离子能级2H11/2/4S3/b2-4I15/2，550nm的绿光对应Er3+离子能级2H11/2/4S3/b-4I15/2。660nm的红光对应Er3+离子能级4F9/2-4I15/2。通过提拉法制备Er3+/Yb3+为1:10的C12A7单晶材料，对其上转换发光特性分析发现绿光和红光都对应着双光子过程。对Er3+掺杂C12A7晶体和纯C12A7晶体的能带结构图进行比较，发现稀土离子的掺入改变了C12A7能带结构，但并没有改变其费米能级的位置。对C12A7与Er掺杂C12A7的结构进行分析，确定了稀土离子并没有进入笼状结构内部，而是以替位的形式存在。在掺入Er后，C12A7的能带宽度增加，其光学吸收范围减小，金属性降低，光电性能增强。分别通过金属还原和氢气还原的方式获得了C12A7:e-，发现掺杂C12A7的导电方式是小极化子导电机制。更多还原

【Abstract】 C12A7is a kind of alternative material of TCO (transparent conductive oxide).Its structure and optical properties would be changed when the inner ions werereplaced. Ions in the cage-like structure of C12A7could be substituted by other ionsthrough implantation, chemical reduction and other ways. Lattice constant wasdetermined by the diameter and state of inner ions. The substitute ions could be e-,H-, Cl-, OH-and F-. These oxygen were replaced and formed a new compound.C12A7sinlge crystal and doped C12A7powder crystal were prepared byCZ(Czochralski) method and solid-phase method respectively in this paper. Processfor growing C12A7single crystal was studied. The research showed that theatmosphere in the furnace, growth rate and temperature condition had greatinfluence on the single crystal, the oxygen content is one of the key factorsdetermining the crystal quality, excessive oxygen content will cause oxidation ofcrucible and introduce coloration and bubble defects, but less content of oxygen willcause the decomposition. When the oxygen content in the melt is higher, dissolvedoxygen will form bubble defects in crystallization process. At the same time, thecrucible material will be oxidized and introdue Ir4+ions. A small amount of bubbledefects could be eliminated by annealing. The optimum technology was thatatmosphere condition was0.5%O2containing N2atmosphere; the raw material wasCaCO3and a-Al2O3; crystal growth temperature was1350°C; lifting speed was1mm/h; the rotating speed was5-10rad/min; the surface temperature was30°C/h;the annealing temperature was1300°C; the temperature gradient was50°C/h.Efects on its optical and electrical properties of C12A7were studied bytheoretical analysis caused by iternal ions. Functional theory and generalizedgradient approximation were selected in quantum chemical methods. The cutoffenergy was340eV; the K point was4×4×4ensuring energy convergence(<10-6eV) calculated. The inner ions affected the properties of C12A7crystalanalysed by quantum chemistry when the polarization was increased with the ions,the Fermi level was increased. The Fermi level of C12A7materials and derivativeswere formed by the inner ions and the framework. A metal bond was formedbetween the frame structure and the free ions. Fermi level of C12A7and itsderivatives were changed when changing the inner ions. C12A7derivatives weregotten by oxidation and reduction respectiively. The ion exchange process wasanalysed through the structure and optical properties. The results showed that C12A7can be oxidized to C12A7:Oin an oxidizing atmosphere, C12A7can bereducted to C12A7:H-in an reducing atmosphere.The Er3+/Yb3+doped C12A7power crystal as prepared by solid reaction. Thecontent of Er3+was1mol%and the contents of Yb3+increased from0%mol to20mol%. Strong green and red emissions were found in the samples which wereincreased with the contents of Yb3+. But the increase of the red emission was greaterthan the green one. In order to analyze the luminescence mechanism of Er3+andYb3+ions, the intensity of red and green light as adjusted to the same ensuring thewhole process, Er ions and Yb ion corresponded the ratio of1:10. Emission of530nm and550nm correspond to the2H11/2/4S3/b2—4I15/2of Er3+. Emission of660nmcorrespond to the4F9/2—4I15/2of Er3+. Er3+/Yb3+C12A7single crystal as prepared byCzochralski method and the upconversion emission was tested. The upconversionluminescence characteristics found in Er3+/Yb3+1:10crystals caused by Effectfrom the segregation coefficient of the dopant ions, the ion concentration in thecrystal has an offset, obtained by adjusting the concentration ratio of1:1red greencrystal doping concentration.Band structure of Er3+-doped C12A7and pure C12A7crystals were comparedto study the effects of doped ions. The results showed that doped ions C12A7hadchanged the band structure but not the Fermi level. C12A7:e-were prepared bymetal reduction and hydrogen reduction. Small polaron conduction mechanism asfound by testing conductiveity. Theoretical analysis on C12A7compared with Erdoped C12A7showed that no rare earth ions entered into interior of the cage-likestructure, but a substitutional ion. The bandwidth of Er3+doped C12A7wasincreased and the optical absorption range was decreased compared with C12A7, sothe metal properties were increased in Er3+doped C12A7.更多还原