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

该项目解决了与蓝色、X射线存储和光激励磷光体材料、绝缘氧化物和硫化物晶格中的二价（Eu 2+、Sm 2+）和三价（Ce 3+）稀土离子的能级结构和效率相关的基本问题。这些材料目前正在使用或考虑用于包括可调谐蓝色固态激光器、电致发光显示器的蓝色磷光体组分、用于医学成像的X射线存储磷光体以及基于电子捕获或光谱烧孔的光学存储器的应用。关键材料的问题有关的性能，这些应用程序的拟议材料包括依赖的5D？4F发光跃迁的主机晶格结构和键合，激发5D水平的关系，主机晶格的能带结构，和机制的激发和刺激过程中的共激活材料。这些问题中的第一个需要能够预测局部配位环境，缺陷，晶体场强度和键合共价的5D水平的能量和分裂的影响。第二个问题涉及的位置的激发5d水平相对于导电带边和其后果的光电离，热化，和电子转移。第三个问题涉及电荷迁移，共激活剂之间的相互作用，和缺陷介导的现象。该方法是基于使用高压来改变蓝UV发射、X射线存储和光激励磷光体材料中的晶格结构、局部配位环境、5d能态、缺陷能态和宿主晶格能带结构。通过控制基本的电子和结构因素，负责确定磷光体的性能，新的见解是寻求激发，发射，存储和刺激机制。建议的工作的目标包括：了解4f n-1 5d的能量和强度的依赖？4f n电子跃迁在Ce 3+，Eu 2+，和Sm 2+激活的荧光粉上的局部配位环境，检查5d电子状态对4f到？4f发光跃迁;研究了Ce 3+、Eu 2+和Sm 2+激活的荧光粉中相对于主晶格导带的5d电子态能量及其对发光、光电离和光激励过程的影响，确定了共价性和晶场强度在确定基于Ce 3+和Eu 2+的蓝色和UV荧光粉中发射5d能级能量中的相对重要性;阐明了Eu 2+激活的混合卤化物X射线存储荧光粉和Eu 2+、Sm 3+共激活的光激励荧光粉中的基本激发、存储和光激励过程;研究了压力对Eu 2+激活的混合卤化物X射线存储荧光粉中F中心形成和聚集的影响X射线和紫外辐射的存在;证明了高压研究的能力，通过磷光体性质与能带结构、电子状态、共价性和晶体场效应的相关性，有助于在环境条件下的预测能力。该项目涉及材料科学专题领域的基础研究问题，具有高度的技术相关性。这些研究有望提高对限制固态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基本和技术上重要的领域对学生进行培训来整合研究和教育。***

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. ***