【作者】 王友发；

【导师】 阮永丰；

【作者基本信息】 天津大学 ， 材料物理与化学， 2013， 博士

【摘要】 YVO4晶体是一种优秀的双折射、铁电晶体，具有四方晶系结构，空间群为D194h（I41/amd）。其晶胞参数为a=b=0.71192nm，c=0.62898nm。它有着较宽的透光范围、易于生长等优良性能，目前，它已成为优异的非线性光学晶体和激光基质晶体。Ce3+是一种重要的稀土离子，由于它能级结构较为简单，并具有较宽的吸收带和发射带，发光过程中量子效率高，既可作为发光激活离子使用，也可作为敏化离子使用，因而在稀土掺杂荧光粉中，有着非常重要的应用。它在地球上的含量较丰富，价格低廉，且容易从矿物中得到。Eu3+是另一种重要的稀土离子，它的特征发射位于红光区域，是典型的线状光谱，早期大量应用于彩色电视机等显示设备，目前是开发红色荧光粉的主流等，它可以直接用红色荧光粉，也可以配合其他荧光粉，用于改善发光材料的显示指数。白光LED相对于传统的照明技术而言，具有能效高、能耗低、无污染、寿命长、安全等诸多优点，它成为当今天科技研究的热点，它已成为现代固体照明的主体，可以预言，它将成今后照明的大势所趋，不可阻挡。因此，开发高效白光LED以及降低它的制造成本，已成为目前固体照明的研究重点。首先，本实验室使用提拉法生长了一系列的YVO4晶体及其掺杂的晶体，并在晶体生长工艺上投入了大量的精力。研究了它们的生长过程，并改进生长工艺，以使晶体质量得到提高，生长效率也进一步提高。另外，本实验室还首次生长了高质量的Ce3+/Eu3+:YVO4晶体。其次，对Ce3+:YVO4晶体的光谱特性展开了一系列的研究。研究了Ce3+:YVO4晶体在不同的激发波长下的发光特性和发光机理，研究了它的吸收谱、激发谱和发射谱与Ce3+能级的关系。研究了掺铈（Ce）YVO4晶体中Ce3+和O2-的价态问题，发现并确认了在YVO4晶体中，Ce3+和Ce4+总是共存的。由于Ce3+和Ce4+的共存，构成了“Ce-O”的电荷迁移态（CTS），并以“分子轨道论”的观点给以定性的解释，从而揭示了在Ce3+:YVO4晶体有着不同寻常的发光特性的机理所在。通过研究还发现，在Ce3+:YVO4晶体中还存在着一种特殊的发光—上转换发光，这种发光是也是基于“Ce-O”的电荷迁移态。Ce3+:YVO4晶体中掺入Eu3+以与改善材料的发光特性，研究了Ce3+/Eu3+:YVO4晶体的光谱特性，讨论了Ce3+和Eu3+的能级特点和能量传递情况，并与Ce3+:YVO4晶体的发光情况作了比较。通过对Ce3+:YVO4晶体光谱的研究发现，Ce3+:YVO4晶体可能成为了种新型的紫外激发的高效蓝光荧光粉，并在激光照射下用肉眼看到了它的蓝光发射。Ce3+/Eu3+:YVO4晶体的光谱特性表明，它在紫外光的激发下发射红光，将有希望成为一种新型的红色荧光粉，在激光照射下可以用肉眼看到它的红光发射。另外，它在近紫外光（397nm）的激发下，通过计算它的CIE坐标发现，它的发光正好位于白光区域，也就是说，它将有希望成为一种使用单一荧光粉就可以发出白光的荧光粉。通过Ce3+:YVO4晶体和Ce3+/Eu3+:YVO4晶体的光谱特性研究，讨论了它们在白光LED中的应用。更多还原

【Abstract】 YVO4crystal is an excellent birefringence and ferroelectric crystal. The structureis tetragonal and the space group isD194h(I41/amd). The cell parameters are a=b=0.71192nm, and c=0.62898nm. It has a wide transparency range, easy to growth andexcellent performance. Currently, it has become an excellent non-linear optical crystaland laser host crystal.Ce3+is an important rare earth ion. Because its energy level is relatively simple,and it has a wide absorption band, emission band, and high quantum efficiency of thelight emitting process. Thus, it can be used as a light emitting activator, and it can alsobe us ed as a s ensitizer. It ha s ve ry i mportant a pplications i n t he r are-earth-dopedphosphors. Another, the content of Ce3+on earth is rich, inexpensive, and easy to getfrom the mineral.Eu3+is another important rare earth. Its intrinsic emission in the red area is typicalof the line spectra. Eu3+ions are used extensively for early color television sets andother display devices. Currently, Eu3+has become the mainstream development of thered phosphor. It can be the activator of red phosphor directly, and it can also improvethe display index of the luminescent materials.The white LED has many advantages, such as high energy efficiency, low energyconsumption, pol lution-free, l ong life t ime, s afety and so on. At the moment, itbecomes more and more important in the scientific and technological research. It hasbecome the subject of modern solid-state lighting and it will become the future trendof the times, unstoppable. Therefore, the development of highly efficient white LEDhas become a research focus of the solid-state lighting.First of all, a series of high-quality Ce3+:YVO4, Ce3+/Eu3+:YVO4crystals and othercrystals were grown. The growth process has been studied, and the growth processand the crystal quality is improved. The efficiency of the crystal growth is furtherimproved. In addition, the high quality of Ce3+/Eu3+:YVO4crystal has been grown forthe first time.Second, in the spectral characteristics of a s eries of Ce3+:YVO4crystals has beenresearched. The light-emitting characteristics and the luminescence mechanism arestudied when the Ce3+:YVO4crystals are excitated under different wavelengths. Therelationships between the ene rgy l evels with the a bsorption s pectrum, e xcitationspectrum and emission spectrum have been studied. The valence of the cerium ion and the oxygen ion in YVO4crystal h as beenstudied. It has been found that the Ce3+ion and the Ce4+ion always coexist together.The “Ce-O” charge transfer state (CTS) has been formed, due to the coexistence ofCe3+and Ce4+, which reveals the mechanism of unusual luminescence properties ofCe3+:YVO4crystal. The "molecular orbital theory" is used to explan this phenomena.An unusual upconversion luminescence in the Ce3+:YVO4crystal has been found.We have found that this special luminescence is also due to the charge transfer state of“Ce-O”.Eu3+ions have been doped into the Ce3+:YVO4crystal, in order to improve thelight-emitting characteristics of the materials. The spectral characteristics of Ce3+/Eu3+: YVO4crystal have been studied, and the energy levels of Ce3+and Eu3+andenergy t ransfer ha s be en discussed. Compared t o t he C e3+:YVO4crystal, theluminescence of Ce3+/Eu3+:YVO4crystal is unique.It i s found t hat C e3+:YVO4crystals m ay b ecome a n ew ki nd of efficientultraviolet blue phosphors from the spectrum of the Ce3+:YVO4crystals. The bluelight has been seen by naked eyes when the Ce3+:YVO4crystals is excited by the laserirradiation.The Spectrum of the Ce3+/Eu3+:YVO4crystals show that it radiate red light underultraviolet l ight, w hich can b e s een b y n aked eyes. It w ill be a ne w type of redphosphors. In addition, under the excitation of near ultraviolet light (397nm), CIEcoordinates are cal culated from t he em ission spectrum. We ha ve f ound t hat t hecoordinates are exactly in white light light-emitting area. That is to say that, it willhopefully become a phosphor which can emit white light by a single phosphor.The l uminescent cha racteristics of t he C e3+:YVO4crystal and Ce3+/Eu3+:YVO4crystals in the application of white LED are discussed.更多还原