稀土掺杂氟化物上转换材料的第一性原理研究与实验制备

发布时间：2018-02-25 04:25

  本文关键词： 太阳能电池 上转换发光 NaYF4 第一性原理 水热法　出处：《燕山大学》2014年硕士论文　论文类型：学位论文

【摘要】：稀土掺杂上转换材料可以将不能被硅太阳能电池吸收利用的红外光转换为能够被其吸收利用的可见光，从而增加硅太阳能电池对太阳光谱的利用率。稀土掺杂上转换材料的基质和稀土掺杂元素均对其发光性质有重要影响。本文通过第一性原理方法研究不同上转换基质材料及不同稀土元素掺杂的NaYF4上转换材料的性质，并通过水热法制备NaYF4:Er/Yb，研究反应时间、反应温度及pH值对样品物相和形貌的影响。确定最佳工艺参数后，分别制备NaYF4:Ho/Yb、 NaYF4:Er/Yb及NaYF4:Tm/Yb，并研究各个样品的发光性质。 通过对β-NaYF4、β-NaYbF4及β-NaLuF4三种上转换基质材料的第一性原理研究发现，β-NaLuF4体系的稳定性高于其他两个体系，β-NaYF4体系在红外光区域的吸收率和反射率在三者中均为最低，这有利于减少激发光的损失，从而提高激发光利用率。 通过对Dy、Ho、Er、Tm、Yb五种不同稀土元素单掺杂的β-NaYF4体系的第一性原理研究发现，，五种不同离子掺杂后，体系的晶胞体积均略有减小。除了Yb掺杂体系在红外光区域有较为明显的吸收外，其他稀土掺杂体系在红外光区域均无明显吸收，这正是稀土单掺杂上转换材料发光效率较低的原因之一。反射方面，在红外光区域Yb掺杂体系反射最为明显，Er掺杂体系反射率最低。 利用水热法，通过在不同工艺参数下制备NaYF4:Er/Yb发现，反应时间的延长以及酸性条件有利于β-NaYF4相的生成，随着反应温度的提高，产物由α-NaYF4相逐渐转变为β-NaYF4相，并且温度进一步升高不会改变产物物相，但会使样品中晶体缺陷增多，颗粒分散性变差。在反应时间为24h，反应温度为180℃，pH=3的工艺条件下，制备NaYF4:Ho/Yb，NaYF4:Er/Yb及NaYF4:Tm/Yb，产物均为纯β-NaYF4相，并且晶型完整。NaYF4:Tm/Yb在800nm处有非常强的发光峰，这一波长恰好处于硅太阳能电池对太阳光吸收利用率最高的波段，因此NaYF4:Tm/Yb对于提高硅太阳能电池光电转换效率具有潜在的应用价值。
[Abstract]:Rare earth doped upconversion materials can convert infrared light that cannot be absorbed by silicon solar cells into visible light that can be absorbed and utilized by silicon solar cells. In order to increase the utilization ratio of solar spectrum of silicon solar cells, the matrix and rare earth doped elements of rare earth doped up-conversion materials have important influence on their luminescent properties. In this paper, different up-conversion is studied by first-principles method. Properties of matrix materials and NaYF4 upconversion materials doped with different rare earth elements, The effects of reaction time, reaction temperature and pH value on the phase and morphology of NaYF4: er / Yb were studied. After determining the optimum process parameters, NaYF4: Hor-Yb, NaYF4:Er/Yb and NaYF4: Tm / Yb were prepared, and the luminescent properties of each sample were studied. Through the first principle study of 尾 -NaYF4, 尾 -NaYbF4 and 尾 -NaLuF4 upconversion matrix, it is found that the stability of 尾 -NaLuF4 system is higher than that of the other two systems, and the absorptivity and reflectivity of 尾 -NaYF4 system are the lowest in the infrared region. This is beneficial to reduce the loss of excitation light, thereby increasing the utilization rate of excitation light. Through the first principle study of the five 尾 -NaYF4 systems doped with different rare earth elements, it is found that the lattice volume of the system decreases slightly after doping with five different ions, except that the Yb doped system has obvious absorption in the infrared region. Other rare earth doped systems have no obvious absorption in the infrared region, which is one of the reasons for the low luminescence efficiency of rare earth mono-doped up-conversion materials. The reflectance of Yb doped Yb doped system is the most obvious in infrared region, and the reflectivity of er doped system is the lowest. By hydrothermal method, NaYF4:Er/Yb was prepared under different process parameters. It was found that the prolongation of reaction time and acidic conditions were favorable to the formation of 尾 -NaYF4 phase. With the increase of reaction temperature, the product gradually changed from 伪 -NaYF4 phase to 尾 -NaYF4 phase. Moreover, further increase of temperature will not change the phase of the product, but it will increase the crystal defects and the dispersion of the particles. Under the conditions of reaction time of 24 h and reaction temperature of 180 鈩

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