极端条件下几种稀土盐和氧化锑的相变和发光研究

发布时间：2018-06-03 18:29

本文选题：高温 + 高压　；参考：《中国科学技术大学》2017年博士论文

【摘要】：温度、压力作为决定物质状态的两个重要物理参量,在改变物质结构,引起相变等方面起着重要作用。压力可以缩短原子间的距离,调整晶体结构和电子轨道,而温度则可以帮助表面活性能来克服不同的结构之间的势垒。物质的各种物理化学性质依赖于物质的结构、尺寸和形貌等。因此,包括低温、高温、高压在内的极端条件可以改变物质的存在状态,获得在常温常压下所隐藏的新奇现象。本文主要制备了各种不同大小和形貌的发光材料,研究温度压力等对材料结构、形貌、尺寸的改变,探究样品在极端条件下物理化学特性,为优异新材料的探索提供线索。全文共有六章,内容如下:第一章、对高压技术和实验方法,高压领域的部分进展及发光材料做了简要介绍。第二章、用水热法合成了六方相NaYF_4:Yb,Ln微米晶。首先对NaYF_4:Yb,Ho微米晶在高温下的上转换和下转换发光强度分别进行了研究。在加热至500℃并降温的过程中,两种不同类型的发光强度一直在增加。降至室温后,上转换和下转换发光强度分别是未加热前的数百和几十倍。结合XRD,红外吸收光谱,吸收光谱以及电子自旋共振光谱,我们认为加热处理去除了样品表面和内部残留的有机基团使上转换发光增强,而生成的C=C等不饱和键使下转换发光增强。同时我们研究了在不同温度和高压下稀土掺杂NaYF_4的上转换光谱。Er的热耦合能级2~H_(11/2)和4~S_(3/2)的比值随温度增加而减小,其规律可用来测量100-700 K之间的温度。该热耦合能级发光强度之比在高压下也发生单调变化,亦可用以测量压力的变化。第三章、结合水热和高温退火的方法合成了 YV0_4:Yb,Er荧光粉,并对各项条件进行了优化处理,该荧光粉可以同时实现下转换和上转换两种发光。可将其应用于太阳能电池,同时实现紫外和红外到可见的光能转化。随后又合成了一系列Tm_3+,Er_3+,Ho_3+和Yb_3+掺杂YVO4的上转换荧光粉,它们分别发射的蓝光,绿光和黄光。尝试着用合成的上转换荧光粉分别组装了可以蓝光、绿光和红光的上转换LED。通过调整Ho_3+、Tm_3+的掺杂比例,实现了上转换白光,其在CIE坐标中接近标准白光。从变温上转换光谱看,将YV0_4:Yb,Tm,Ho用作白光LED时,应考虑其荧光的温度效应。第四章、用水相反应法分别合成了纯的正交相和六方相的EuF_3纳米晶。高压荧光光谱表明,正交相EuF_3转变为六方相的压力点比块材高约1.5 GPa。与在静水压下的一直稳定存在不同,六方相EuF_3会在非静水压下经历从六方到正交然后再回到六方的循环相变。其从六方到正交的相变压力很小(0.07 GPa),3～10 GPa又从正交相变回六方相。同样的,六方相EuF_3在高温下也会经历从六方到正交然后再回到六方的循环相变。第五章、用水热和溶剂热法合成了立方Sb_20_3微米晶和正交Sb_20_3纳米带。采用原位高压拉曼的方法研究了立方Sb2O3微米晶在常温的结构稳定性。在高于25 GPa的压力下,Sb_20_3转变为高密度的非晶相,激光辐照可以促进该过程。数分钟的辐照可以将完全相变所需的压力从大于35 GPa降至27 GPa。完全卸压后,非晶相可以部分重新变为立方相,激光辐照同样可以加速该过程。采用拉曼光谱和同步辐射XRD的方法对其在高压下的相变进行了研究,高压拉曼和高压XRD结果都表明,正交相Sb_20_3纳米带在13 GPa转变为一个结构未知的高压相。第六章对研究工作做了总结。
[Abstract]:Temperature, pressure, as the two important physical parameter determining the state of the material, plays an important role in changing the structure of the material and causing the phase transition. The pressure can shorten the distance between the atoms, adjust the crystal structure and the electron orbit, and the temperature can help the surface activity to take the barrier between different structures. The chemical properties depend on the structure, size and morphology of the material. Therefore, the extreme conditions, including low temperature, high temperature and high pressure, can change the state of the material and obtain the novelty hidden under the normal temperature and atmospheric pressure. In this paper, various luminescent materials of different sizes and morphologies have been prepared, and the structure and structure of temperature and pressure on the material are studied. The physical and chemical properties of the samples under extreme conditions are explored to provide clues to the exploration of excellent new materials. There are six chapters in the full text as follows: in Chapter 1, a brief introduction to high pressure technology and experimental methods, some progress in the field of high pressure and luminescent materials is briefly introduced. The second chapter, the synthesis of six square phase NaYF_4:Yb, Ln micro At first, the upconversion and down conversion luminescence intensities of NaYF_4:Yb, Ho microcrystals at high temperature were studied. During heating to 500 C and cooling, the two different types of luminescence intensities have been increasing. After reducing to room temperature, the upconversion and down conversion luminescence intensities are hundreds and dozens times as many times as before unheated. Combined with XRD, In the infrared absorption spectrum, absorption spectrum and electron spin resonance spectrum, we think that the upconversion luminescence is enhanced by the removal of the residual organic groups in the surface and inside of the sample, while the generated C=C and other unsaturated bonds enhance the down conversion luminescence. At the same time, we studied the upconversion light of the rare earth doped NaYF_4 at different temperatures and high pressures. The ratio of the thermal coupling energy level 2~H_ (11/2) and 4~S_ (3/2) of the spectrum.Er decreases with the increase of temperature. The law can be used to measure the temperature between 100-700 K. The ratio of the luminescence intensity of the thermal coupling energy level also varies monotonically at high pressure, and can also be used to measure the change of pressure. The third chapter, combined with the methods of water heat and high temperature annealing, syntheses YV0_4:Yb, E The R phosphor is optimized and the conditions are optimized. The phosphor can simultaneously realize down conversion and upconversion two kinds of luminescence. The phosphor can be used in solar cells, and the ultraviolet and infrared to visible light energy conversion can be realized. Then a series of Tm_3+, Er_3+, Ho_3+ and Yb_3+ doped YVO4 up-converted phosphors are synthesized. The blue light, green light and yellow light are launched. The upconversion LED., which can be blue, green and red, is assembled by using the synthetic upconversion phosphor. The up conversion white light is realized by adjusting the proportion of Ho_3+ and Tm_3+, which is close to the standard white light in the CIE coordinates. From the variable temperature conversion spectrum, the YV0_4:Yb, Tm and Ho are used as white LED. The temperature effect of its fluorescence is considered. In the fourth chapter, the pure orthogonal and six square phase EuF_3 nanocrystals are synthesized by the aqueous phase reaction method. The high pressure fluorescence spectra show that the pressure point of the orthogonal phase EuF_3 transformation to six square phase is about 1.5 GPa. higher than that of the block material, and the six square phase EuF_3 will experience under the non hydrostatic pressure. The cyclic phase transition from the six party to the orthogonal and then back to the six party. The phase transition pressure from the six to the orthogonal (0.07 GPa) and the 3~10 GPa from the orthogonal phase transition back to the six square phase. The same, the six square phase EuF_3 will also undergo the cyclic phase transition from six to the orthogonal and then back to the six party. The structure stability of cubic Sb2O3 micron crystal at normal temperature is studied by in situ high pressure Raman spectroscopy. Under the pressure of higher than 25 GPa, Sb_20_3 is transformed into a high density amorphous phase. The laser irradiation can promote the process. A few minutes of irradiance can increase the pressure required for the complete phase transition from more than 3. After the 5 GPa is reduced to 27 GPa. completely, the amorphous phase can be partially converted into cubic phase, and the laser irradiation can also accelerate the process. The phase transition under high pressure is studied by Raman and synchrotron radiation XRD. The results of High Pressure Raman and high pressure XRD show that the orthogonal Sb_20_3 nanoribbons are converted to a node in 13 GPa. The sixth chapter summarizes the research work.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O482.31

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