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

镧系掺杂的上转换荧光粉（UCP）材料可以吸收一个或多个低能光子，然后通过一种独特的称为上转换的光致发光过程发射一个高能量、低波长的光子。能够将红外辐射转化为可见光的UCP纳米晶体在过去十年中得到了深入的研究，并且已经开始在太阳能和生物医学应用中出现。我们在此认识到利用UCP纳米晶体的巨大潜力，这种纳米晶体被设计成将普通可见光转化为杀菌紫外线辐射，从而创造出高度创新的生物杀灭表面技术，即暴露在可见光下使微生物失活的表面。虽然文献中已经存在少数可见到紫外线的上转换材料，但它们的转换效率被认为太低，无法用于实际的杀菌剂应用。然而，基于红外到可见光上转换技术的最新进展，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，并在低功率阳光或室内环境光条件下实现紫外线发射；（ii）这种改进可以通过精心选择镧系掺杂剂组合、低振动基质和纳米结构优化来实现。他们进一步假设，精心设计的纳米晶体紫外发光荧光粉涂层表面将显示出杀灭生物的效果，为现有的抗菌表面提供了一种有效、经济、可持续的替代方案，以阻止病原体的转移。该研究的主要重点是探索基本的纳米荧光粉设计策略，从而在杀菌范围内有效地将宽带可见光上转换为紫外线光子，从而在涂覆在表面时有效地杀灭生物。上转换纳米晶体将通过溶胶-凝胶分解和水热技术通过不同的镧系掺杂剂组合、宿主晶体和纳米结构修饰来合成。能量传递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。材料将使用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作用将分别通过动力学活力测定和扫描共聚焦激光显微镜测定，使用各种测试微生物。知识的优点。工程上转换纳米荧光粉用于光活化杀菌剂表面开发的想法在文献中从未被探索过。提出的研究将为紫外发射上转换纳米磷光合成策略、材料表征和环境技术适用性提供基础的第一步知识。本研究还将回答以下基本问题：(i)众所周知的IR-to-visible上转换和visible-to-UV上转换过程之间的异同；以及（ii）促进宽范围激发波长转换的设计方面。更广泛的影响。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，减少对连续化学应用的依赖。长期以来，在医院、食品工业和公共场所抑制病原体转移的表面是一种受欢迎的工具，同时我们还设想将其应用于发展中国家的太阳能水消毒套件。教育本科生和研究生是拟议项目的一个组成部分，并将为参与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卓越的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.