Design, Synthesis and Modeling of Luminescent Ceramics for Application in Solid State Lighting

非技术描述：照明占美国总用电量的22%，相当于每年在照明上花费500亿美元，同时化石燃料工厂向大气排放1.3亿吨碳。基于蓝色发光二极管和发光粉(荧光粉)的固态照明已经成为取代白炽灯和荧光灯的高效、持久的光源。美国白光LED的荧光粉市场目前为5亿美元/年，预计到2015年将达到10亿美元/年。对于这些新的节能设备来说，可靠和系统地识别具有高量子效率和热稳定性的新荧光粉是至关重要的。纳米磷光体是减少光散射的一个令人兴奋的机会，从而提高了提取效率。这项工作是跨学科的，跨越材料科学、光学性质、化学和原子尺度建模等领域，包括实验和建模。研究生接受复杂的电子显微镜技术、理论和计算方法方面的培训。多样性努力正在继续并得到加强。西班牙裔服务机构的学生和为低收入学生服务的初中/高中的参与也包括在内。为研究生课程开发了新的课程。技术细节：固态照明，基于蓝光(450 Nm)发光二极管(LED)和发光粉(荧光粉)，已成为高效、持久的光源，取代白炽灯和荧光灯。在近紫外光(370-410 nm)发射的新型二极管最近被认为是可以提高光源提取效率的芯片。这一新的发展需要在纳米范围内发现新的荧光粉系统，以充分利用这项新技术。这项工作中使用的荧光粉是含有少量激活剂(稀土元素)的宽带隙材料(主体)。根据主机：激活剂的组合，可以获得可见光光谱上的颜色。本项目旨在验证以下三个假设：(1)使用与第一性原理建模相结合的经验方法，可以确定近紫外白光LED发光光源的新的高量子效率、热稳定的荧光粉；(2)可以确定并有望克服纳米荧光粉的低量子效率；(3)结合半局域和混合密度泛函理论进行建模，将有助于深入了解新荧光粉体系的光子吸收和发射机制、物相、化学和热稳定性以及纳米荧光粉的量子效率。通过各种实验和计算任务验证了这些假设：(1)激发能位于370-410 nm近紫外光谱范围内的荧光粉的设计，(2)通过复杂官能团的激发进行敏化的荧光粉的设计，(3)结合分析工具，将采用系统的方法来评估纳米荧光粉(200 Nm)量子效率低的原因。表面和体相分析将确定激活剂的局部环境和猝灭发光的陷阱，以及(4)用一系列第一原理方法研究要合成和实验测试的荧光粉材料的相稳定性、水稳定性、热稳定性和电子结构。理论计算用于指导和解释实验，并指导哪些成分和结构的荧光粉最有希望应用于紫外光LED。

NON-TECHNICAL DESCRIPTION: Lighting accounts for 22% of the total US electrical energy use, which translates to $50 billion per year spent on lighting accompanied with 130 million tons of carbon emitted into the atmosphere from fossil fuel plants. Solid state lighting, based on blue-emitting light emitting diodes with a luminescent powder (phosphor), has emerged as highly efficient, long lasting light sources to replace incandescent and fluorescent lighting. The phosphor market in the US for white-emitting LEDs is currently $500M/year and is expected to reach $1B/year by 2015. Identifying new phosphors in a reliable and systematic way with high quantum efficiency and thermal stability is crucial for these new energy saving devices. Nanophosphors represent an exciting opportunity to reduce light scattering, thereby improving the extraction efficiency. This work is interdisciplinary and spans the fields of materials science, optical properties, chemistry, and atomic scale modeling that involves both experiments and modeling. Graduate students are trained in sophisticated electron microscopy techniques, theoretical and computational methods. Diversity efforts are continued and strengthened. The involvement of students from a Hispanic-serving Institution and a middle/high school that serves low-income students are included. New classes are developed for the graduate curriculum.TECHNICAL DETAILS: Solid state lighting, based on blue-emitting (450 nm) light emitting diodes (LEDs) with a luminescent powder (phosphor), has emerged as highly efficient, long lasting light sources to replace incandescent and fluorescent lighting. New diodes that emit in the near UV (370-410 nm) have recently been recognized as chips that could improve the extraction efficiency of the light source. This new development requires the discovery of new phosphor systems in the nano-sized range to fully exploit this new technology. The phosphors used in this work are wide band gap materials (hosts) that contain a small amount of activator (rare-earth element). Depending on the host:activator combination, colors across the visible spectrum can be obtained. This project aims at validating the following three hypotheses: (1) using an empirical approach combined with first principles modeling, new high quantum efficiency, thermally stable phosphors can be identified for near UV LED white-emitting light sources, (2) the low quantum efficiency of nanosized phosphors can be determined and perhaps overcome and (3) modeling using a combination of semi-local and hybrid density functional theory will provide insight on the mechanisms for photon absorption and emission of new phosphor systems, the phase, chemical and thermal stability and on the quantum efficiency of nanosized phosphors. These hypotheses are tested by conducting by a variety of experimental and computational tasks: (1) the design of phosphors in which the excitation energy lies in the near UV spectral range of 370-410 nm, (2) the design of phosphors in which sensitization is via the excitation of complex functional groups, (3) using a combination of analytical tools, a systematic approach will be conducted to evaluate the factors behind the low quantum efficiency of nanosized phosphors ( 200 nm). Surface and bulk analyses will identify the local environment of the activator and the traps that quench the luminescence and (4) a hierarachy of first principles methods are used to investigate the phase stability, aqueous stability, thermal stability and electronic structure of the phosphor materials to be synthesized and tested experimentally. The theoretical calculations are used to guide and interpret experiments and also to guide which compositions and structures of the phosphor materials are most promising for UV LED applications.