Relationship of Electronic States to d -> f Emission Efficiency of Lanthanide Activated Phosphors

该项目研究了绝缘氧化物和硫化物晶格中二价(Eu2+，Sm2+)和三价(Ce3+)稀土离子的蓝光、X射线存储和光激励发光材料的能级结构和效率等基本问题。这些材料目前正被用于或考虑用于应用，包括可调谐的蓝色固态激光器、电致发光显示器的蓝色荧光粉组件、用于医学成像的X射线存储荧光粉、以及基于电子捕获或光谱空穴燃烧的光学存储器。与所提出的材料性能相关的关键材料问题包括：5d-4F发光跃迁与主体晶格结构和成键的关系，激发态5d能级与主体晶格能带结构的关系，以及共激活材料中激发和刺激过程的机制。第一个问题要求能够预测局域配位环境、缺陷、晶场强度和成键共价性对5d能级的能量和分裂的影响。第二个问题涉及激发的5d能级相对于导带的位置及其对光电离、热化和电子转移的影响。第三个问题涉及电荷迁移，共激活剂之间的相互作用，以及缺陷介导的现象。该方法基于高压改变蓝紫外光发射、X射线存储和光激励发光材料中的晶格结构、局域配位环境、5d能态、缺陷能态和主体晶格能带结构。通过控制决定荧光粉性质的潜在电子和结构因素，寻求对激发、发射、存储和刺激机制的新见解。这项工作的目标包括：了解Ce3+、Eu2+和Sm2+激活的荧光粉中4Fn-15d到？4Fn电子跃迁的能量和强度对局域配位环境的依赖；考察5d电子态对4f到？4F发光跃迁的影响；研究5d电子态相对于主体晶格导带的能量及其对Ce3+、Eu2+和Sm2+激活的荧光粉发光、光电离和光刺激过程的影响；确定了共价性和晶场强度对确定基于Ce3+和Eu2+的蓝色和UV荧光粉发射5d能级的相对重要性，阐明了Eu2+激活的混合卤化物X射线存储荧光粉和Eu2+，Sm3+共激活的光刺激荧光粉的基本激发、存储和光刺激过程，研究了在X射线和UV辐射存在下，压力对Eu2+激活的混合卤化物存储荧光粉F中心形成和聚集的影响；展示高压研究的能力，通过荧光粉性质与能带结构、电子态、共价性和晶场效应的关联，为环境条件下的预测能力做出贡献。%该项目解决具有高度技术相关性的材料科学主题领域的基础研究问题。这些研究有望提高对限制固体激光材料和各种光学显示应用效率的因素的基本理解。该计划的一个重要特点是通过在一个具有根本意义和技术意义的领域对学生进行培训，将研究和教育结合起来。***

This project addresses fundamental questions associated with the energy level structure and efficiency of blue, x-ray storage and photostimulable phosphor materials, divalent (Eu 2+ , Sm 2+ ) and trivalent (Ce 3+ ) rare earth ions in insulating oxide and sulfide lattices. These materials are currently being used or considered for applications that include tunable blue solid state lasers, the blue phosphor component of electroluminescent displays, x-ray storage phosphors for medical imaging, and optical memory based on electron trapping or spectral holeburning. Key materials issues relevant to the performance of the proposed materials for these applications include the dependence of 5d to ?4f luminescence transitions on host lattice structure and bonding, the relationship of excited 5d levels to the band structure of the host lattice, and mechanisms of excitation and stimulation processes in co-activated materials. The first of these issue requires the ability to predict effects of local coordination environment, defects, crystal field strength and bonding covalency on the energies and splittings of the 5d levels. The second issue concerns the position of the excited 5d levels relative to the conduction bandedge and its consequences for photoionization, thermalization, and electron transfer. The third issue involves charge migration, interactions between co-activators, and defect mediated phenomena. The approach is based on using high pressure to vary lattice structure, local coordination environment, 5d energy states, defect energy states and host lattice band structure in blue-UV emitting, x-ray storage and photostimulable phosphor materials. Through control of underlying electronic and structural factors responsible for determining phosphor properties, new insight is sought into excitation, emission, storage and stimulation mechanisms. The objectives of the proposed work include: understanding the dependence of the energy and intensity of 4f n-1 5d to ?4f n electronic transitions in Ce 3+ -, Eu 2+ -, and Sm 2+ -activated phosphors on local coordination environment; examining the influence of 5d electronic states on 4f to ?4f luminescence transitions; investigating the energy of 5d electronic states relative to the host lattice conduction band and its effect on luminescence, photoionization, and photostimulation processes in Ce 3+ -, Eu 2+ -, and Sm 2+ -activated phosphors; determining the relative importance of covalency and crystal field strength in establishing the energy of the emitting 5d level in blue and UV phosphors based on Ce 3+ and Eu 2+ ; elucidating the fundamental excitation, storage and photostimulation processes in Eu 2+ -activated mixed halide x-ray storage phosphors and Eu 2+ , Sm 3+ co-activated photostimulable phosphors; examining the effect of pressure on F-center formation and aggregation in Eu 2+ -activated mixed halide storage phosphors in the presence of x-ray and UV radiation; demonstrating the ability of high pressure studies to contribute to predictive capability at ambient conditions through correlations of phosphor properties with band structure, electronic states, covalency and crystal field effects.%%% The project addresses basic research issues in a topical area of materials science with high technological relevance. These studies are expected to improve fundamental understanding of factors limiting the efficiency of solid state laser materials and a variety of optical display applications. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area. ***