@article{3233a5e06db546539988013206479b52,
title = "Designing ultraviolet upconversion for photochemistry",
abstract = "Upconversion nanoparticle (UNP) technology has matured to enable cutting edge applications in bioimaging, sensing, and photochemistry. UNPs have garnered wide interest due to the many facets of available material choices, surface modifications and optical properties. With their nonblinking long luminescent lifetimes, large anti-Stokes shift and photostability combined with their relatively small size, they provide a compelling alternative to traditional molecular probes in bioimaging and biosensing applications. In particular, the ability to upconvert photons from near-infrared (NIR) to ultraviolet (UV) allows for the development of site-specific methods of photochemical activation of various functional, theranostic agents. This review summarizes advances in the development of synthetic methods that promote UV luminescence in UNPs. The review is organized into three broad topics: the host, dopants, and architecture. Examples of selected applications that may utilize improved NIR to UV upconversion are included. As the advancements in nanotechnology continue to benefit the fields of biochemistry, medicine, and biology, new paradigms of implementation of UNPs may broaden their clinical appeal.",
keywords = "Drug delivery, Imaging, Nanoparticles, Photochemistry, Theranostics, Upconversion",
author = "Peter Dawson and Marek Romanowski",
note = "Funding Information: Passive shells commonly utilize the host crystal lattice, or similar composition, and are void of sensitizers or activators. These shells are one of the most simple and effective ways to improve luminescent performance [124,142]. Passive shells provide an inert boundary between energetically active ions on surface sites of the core and the dispersant where energy can be commonly lost due to nonradiative decay of excited states [12,142,143]. A major cause of energy loss is the Yb3+ energy migration transferring energy to the surface and that energy being lost in a nonradiative process. This energy loss is apparent in Fig. 5 where core particles see diminished UV output above 50% Yb3+ [12]. However, as Fig. 5 also demonstrates, merely adding a passive shell to the UNP causes Yb3+ doping to provide continuous improvement of UV luminescence up to complete replacement of Y3+ with Yb3+ [12,135,144]. Due to the crystalline nature of UNPs, only certain compatible compositions will support the epitaxial growth of the shell. For example, while hexagonal phase NaYF4:Yb3+,Tm3+ UNP may display improved UV luminescence in comparison to cubic phase UNP of the same composition, only cubic phase UNP is compatible with epitaxial layer of CaF2 [12]. Cubic phase NaYF4:Yb3+,Tm3+ with a CaF2 shell produce more intense UV than their hexagonal phase counterparts with a NaYF4 shell as seen in Fig. 3c.Funding was provided in part by T32 training grants GM084905 and EB000809 from the National Institutes of Health. Funding Information: Funding was provided in part by T32 training grants GM084905 and EB000809 from the National Institutes of Health . Publisher Copyright: {\textcopyright} 2020",
year = "2020",
month = jun,
doi = "10.1016/j.jlumin.2020.117143",
language = "English (US)",
volume = "222",
journal = "Journal of Luminescence",
issn = "0022-2313",
publisher = "Elsevier B.V.",
}