Air‐Stable Silicon Nanocrystal‐Based Photon Upconversion. Issue 17 (3rd June 2021)

• Record Type: Journal Article
• Authors: Xia, Pan; Schwan, Joseph; Dugger, Thomas W.; Mangolini, Lorenzo; Tang, Ming Lee
• Is Part Of: Advanced optical materials. Volume 9:Issue 17(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-06-03
• Subjects: air‐stable upconversion -- methyl oleate -- nontoxic upconversion -- photo‐therapy -- silicon nanocrystals; Optical materials -- Periodicals; Photonics -- Periodicals; 620.11295
• DOI: 10.1002/adom.202100453
• Languages: English
• ISSNs: 2195-1071

Abstract

Abstract: Photon upconversion may have the highest impact in biological applications because incoming photons transparent to tissue can be combined to make visible light useful for photodynamic therapy and imaging. The ability to use semiconductor nanocrystals as light absorbers for photon upconversion is important because their strong absorption profiles are synthetically tunable. In particular, the use of earth‐abundant, environmentally benign silicon quantum dots (QDs) as light absorbers for photon upconversion is very attractive. In this work, the authors demonstrate a general strategy employing both physical and chemical barriers to achieve air‐stable fusion of triplet excitons photosensitized by silicon QDs, crucial to practical applications of photon upconversion. Gel permeation chromatography (GPC) and dynamic light scattering (DLS) show that thermal hydrosilylation critical for colloidal stability and efficient triplet energy transfer creates a polymeric barrier to oxygen. This kinetic barrier to oxygen arises from the presence of cross‐linked surfactants and is complemented by the sacrificial oxidation of silicon QDs itself. Photon upconversion lasted longer than 4 days with quantum yields (QYs) as high as 7.5% (out of a maximum of 50%) using Si QD light absorbers with diphenylanthracene in methyl oleate. Oil‐in‐water micelles are air‐stable for 2 days with absolute upconversion QYs of 5.5%. Abstract : The authors show a general strategy to achieve a 4‐day air‐stable photon upconversion (green/blue light to violet light) photosensitized by non‐toxic silicon nanocrystals. The upconversion quantum yield is as high as 7.5% (out of a maximum of 50%) in methyl oleate and 5.5% in oil‐in‐water micelles with 2‐day air‐stability.