Converting Visible Light to UVC: Lanthanide Upconversion Nano-Phosphors for Light-Activated Biocidal Surface Development

稀土掺杂的上转换发光材料可以吸收一个或多个低能量的光子，然后通过一种称为上转换的独特的光致发光过程发射出一个能量更高、波长更低的光子。能够将红外辐射转换为可见光的UCP纳米晶在过去十年中得到了深入的研究，并已开始在太阳能和生物医学应用中出现。在此，我们认识到利用UCP纳米晶体--将普通可见光转化为杀菌紫外线--在创造高度创新的杀菌表面技术方面的巨大潜力，即当暴露在可见光下时，表面可以灭活微生物。虽然文献中已经存在一些可见光到紫外光的上转换材料，但它们的转换效率被认为太低，无法应用于实际的杀生应用。然而，基于最近在红外到可见光上转换技术方面取得的进展，他们假设：(I)复杂的材料设计将导致更高、更实用的上转换效率，并能够在低功率阳光或环境室内光条件下进行紫外线发射；以及(Ii)这种改进可以通过仔细选择稀土掺杂组合、低振动基质和纳米结构优化来实现。他们进一步假设，经过精心设计的纳米紫外发光材料表面将显示出生物杀菌效果，为目前的抗菌表面提供一种有效、经济和可持续的替代方案，以阻止病原体的转移。拟议研究的主要重点是探索基本纳米荧光粉的设计策略，这些策略能够有效地将宽带可见光上转换为杀菌范围内的紫外线光子，从而在涂层到表面时具有有效的生物杀灭作用。上转换纳米晶体将通过溶胶-凝胶分解和水热技术结合不同的稀土掺杂组合、主体晶体和纳米结构修饰来合成。能量转移过程的效率和机制将使用定制的高能激光光致发光光谱进行测量。材料将通过X射线衍射分析、透射电子显微镜等进行表征。生物杀灭效果和生物膜抑制将分别通过动态活性分析和扫描共聚焦激光显微镜来确定，使用各种测试微生物。工程上转换纳米荧光粉用于光激活杀生表面开发的想法在文献中从未被探索过。这项拟议的研究将为紫外光发射上转换纳米荧光粉的合成策略、材料表征和环境技术适用性提供基础的第一步知识。这项研究还将回答以下基本问题：(I)众所周知的红外到可见光上转换过程和可见光到紫外光上转换过程之间的异同；以及(Ii)促进大范围激发波长转换的设计方面。光转换材料的进步是可持续和绿色技术的关键前沿，因为它允许利用可再生能源，在这种情况下，减少了对持续化学应用的依赖。可以保持无病原体的表面是一种长期受欢迎的工具，用于抑制医院、食品工业和公共场所的病原体传播，同时我们还设想将其应用于发展中国家的太阳能水消毒试剂盒。培养本科生和研究生是拟议项目的一个组成部分，将为参与项目的学生提供在应用固态物理/化学、材料科学、纳米技术和环境工程方面的特殊跨学科和协作学习经验。该项目还将利用现有的高中生暑期实习计划。

Lanthanide-doped upconversion phosphor (UCP) materials can absorb one or more low-energy photons and subsequently emit one higher-energy, lower-wavelength photon via a unique photoluminescence process called upconversion. UCP nanocrystals that are capable of converting IR radiation to visible light have seen intensive research in the past decade and have already begun to emerge in solar energy and biomedical applications. We herein recognize the great potential for exploiting UCP nanocrystals - that are engineered to convert ordinary visible light into germicidal ultraviolet radiation - in creating highly innovative biocidal surface technologies, i.e., surfaces that inactivate microorganisms when exposed to visible light.Hypothesis. While a handful of visible-to-UV upconversion materials already exist in the literature, their conversion efficiencies are considered too low for practical biocidal applications. However, based on the recent advances made in IR-to-visible light upconversion technology, they hypothesize that (i) sophisticated material design will lead to higher, more practical upconversion efficiencies and enable UV-emission under low-power sunlight or ambient indoorlight conditions; and (ii) such improvements can be achieved through careful selection of lanthanide dopant combinations, low vibrational host matrices, and nano-structural optimization.They further hypothesize that surfaces coated with carefully engineered nanocrystalline UV-emitting phosphors will exhibit biocidal effects, providing an effective, cost-efficient, and sustainable alternative to current antimicrobial surfaces for the deterrence of pathogen transfer.Objectives. The primary focus of the proposed research is to explore fundamental nanophosphor design strategies that result in efficient upconversion of broadband visible light into UV photons in the germicidal range and, consequently, effective biocidal action when coated onto surfaces.Approach. Upconversion nanocrystals will be synthesized via sol-gel decomposition and hydrothermal techniques with varying lanthanide dopant combinations, host crystals and nanostructural modifications. The efficiency and mechanisms of energy transfer processes will be gauged using a custom-built high-energy laser photoluminescence spectroscopy. Materials will be characterized using X-ray diffraction analysis, transmission electron microscopy, etc. Biocidal efficacy and biofilm inhibition will be determined via kinetic viability assays and scanning confocal laser microscopy, respectively, using various test microorganisms.Intellectual Merits. The idea of engineering upconversion nanophosphors for light-activated biocidal surface development has never been explored in the literature. The proposed study will provide fundamental, first-step knowledge in UV-emitting upconversion nanophosphor synthesis strategies, material characterization, and environmental technology applicability. This researchwill also answer fundamental questions regarding: (i) similarities and differences between the well-understood IR-to-visible upconversion and visible-to-UV upconversion processes; and (ii)design aspects that promote the conversion of a broad range of excitation wavelengths.Broader Impacts. The advancement of light conversion materials is a critical forefront in sustainable and green technology, as it allows utilization of renewable energy as well as, in this case, decreased reliance on continuous chemical application. Surfaces which can inherently remain pathogen free are a long sought-after tool for inhibiting pathogen transfer in hospitals,food industry, and public areas, while we additionally envision application to solar water disinfection kits for the developing world. Educating undergraduate and graduate students is an integral part of the proposed project and will provide participating students with exceptional interdisciplinary and collaborative learning experiences in applied solid-state physics/chemistry,material science, nanotechnology, and environmental engineering. The project will also leverage an existing high school student summer internship program.