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

该项目解决了与蓝色，x射线存储和光刺激荧光粉材料，二价（Eu 2+, Sm 2+）和三价（Ce 3+）稀土离子在绝缘氧化物和硫化物晶格中的能级结构和效率相关的基本问题。这些材料目前被用于或考虑用于以下应用：可调谐蓝色固态激光器、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存储器。与这些应用中拟议材料的性能相关的关键材料问题包括5d对？主晶格结构和成键上的发光跃迁，激发5d能级与主晶格能带结构的关系，以及共活化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部配位环境、缺陷、晶体场强和键合共价对5d能级的能量和分裂的影响。第二个问题涉及被激发5d能级相对于传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和缺陷介导现象。该方法是基于高压改变蓝紫外发射、x射线存储和光刺激荧光粉材料中的晶格结构、局部配位环境、5d能态、缺陷能态和主晶格带结构。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，储存和刺激机制的新见解。建议的工作目标包括：了解4fn - 15d的能量和强度对？ce3 + -、eu2 + -和sm2 + -活化荧光粉在局部配位环境下的电子跃迁检验5d电子态对4f to ?的影响4f发光跃迁；研究了Ce 3+ -、Eu 2+ -和sm2 + -激活荧光粉的5d电子态相对于主晶格导带的能量及其对发光、光离和光刺激过程的影响；确定共价和晶体场强在建立基于ce3 +和eu2 +的蓝光和紫外荧光粉发射5d能级能量中的相对重要性；阐明了eu2 +激活的混合卤化物x射线存储荧光粉和光刺激的基本激发、存储和过程；研究了在x射线和紫外辐射下压力对Eu 2+活化的混合卤化物存储荧光粉中f中心形成和聚集的影响；展示了高压研究在环境条件下通过荧光粉特性与能带结构、电子态、共价和晶体场效应的相关性来促进预测能力的能力。该项目涉及材料科学中具有高技术相关性的主题领域的基础研究问题。这些研究有望提高对限制固态激光材料效率和各种光学显示应用的因素的基本理解。该计划的一个重要特点是通过培养学生在一个基础和技术上重要的领域的研究和教育的整合。* * *

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. ***