基于稀土4f–5d跃迁窄带发光材料中电子-声子耦合对光谱特性影响的第一性原理研究

基于稀土4f-5d跃迁窄带发光材料应用于白光LED有助于改善其发光性能和实现广色域背光显示。然而，与窄带发射关联的电子-声子耦合的性质和作用仍是有待厘清的基础科学问题。本项目针对Eu2+或Ce3+激活窄带发光材料，设计采用周期性密度泛函理论计算，获得掺杂离子在4f基态和5d最低激发态时稳定构型，得到局域结构弛豫信息；计算体系声子色散谱及晶格振动模式，将其投影分解到掺杂离子配位环境进行振动分析；构造镶嵌团簇，进行组态相互作用加自旋-轨道耦合相对论计算，得到4f−5d跃迁能量和Stokes位移，并将其与局域结构弛豫和振动联系起来。将该方法应用于典型窄带发光材料，分析基质致密性、局域结构对称性等因素影响发射谱带宽度的结构和电子方面原因，理解电子-声子耦合导致窄带发射的物理机制。本研究将为由基质结构和化学组成预测掺杂Eu2+/Ce3+光谱特性提供理论线索，促进新型窄带发光材料的设计和性能优化。

The application of lanthanide 4f-5d transitions-based to white LEDs helps to improve their luminescence performance and to realize backlight display with wide color gamut. However, the nature and role of the electron-phonon coupling that is correlated with the narrow-band emission is not yet clear. This project focuses on Eu2+/Ce3+-activated narrow-band emitting phosphors. Using the periodic density functional theory-based calculations, we will obtain the stable local structures of Eu2+/Ce3+ at the 4f ground and lowest 5d excited electronic states, and the associated information on structural relaxations. Next, we will calculate the phonon dispersion spectrum of the systems to derive the information on lattice vibrations, which will be projected onto the local structure of the dopant. Then, dopant-centered embedded clusters will be constructed, and configuration interaction plus spin-orbit calculations will be performed to obtain 4f-5d transition energies and the associated Stokes shift, which will be correlated with the local structural relaxation and vibrations. By applying the method to a series of typical narrow-band emitting materials, we will analyze the influence of the factor such as crystal density and local symmetry on the emission band width from electronic and structural aspects, to further understand the physical mechanism behind the role of electron-phonon coupling in narrow-band emission. This study will provide important clues to predict the spectroscopic properties of Eu2+/Ce3+-doped materials from the chemical composition and atomic structure of the host crystal, accelerating the development and performance optimization of new narrow-band emitting phosphors.