Employing Core‐Shell Quantum Dots as Triplet Sensitizers for Photon Upconversion

Abstract

A new family of surface-functionalized CdSe/ZnS core-shell quantum dots (csQD) has been developed, which work as triplet sensitizers for triplet-triplet annihilation-based photon upconversion (TTA-UC). The surface modification of csQD with acceptor molecules plays a key role in the efficient relay of the excited energy of csQD to emitter molecules in the bulk solution, where the generated emitter triplets undergo triplet-triplet annihilation that leads to photon upconversion. Interestingly, improved UC properties were achieved with the core-shell QDs compared with core-only CdSe QDs (cQD). The threshold excitation intensity, which is defined as the necessary irradiance to achieve efficient TTA process, decreases by more than a factor of four. Furthermore, the total UC quantum yield is enhanced more than 50-fold. These enhancements should be derived from better optical properties of csQD, in which the non-radiative surface recombination sites are passivated by the shell layer with wider bandgap.

Improved photon absorption in dye-functionalized silicon nanocrystals synthesizedviamicrowave-assisted hydrosilylation

“…The efficient energy transfer between quantum dots and triplet state of dyes attached to its surface was described in literature. [41][42][43] For instance, Mongin et al reported Dexter-like triplet-triplet energy transfer between CdSe nanocrystals and a surface-anchored polyaromatic dye. 43 Recently, Xia et al described triplet-triplet annihilation upconversion utilizing energy transfer from SiNc to the triplet sate of diphenylanthracene anchored with the SiNc surface.…”

Kinetically controlled crystal growth approach to enhance triplet energy migration-based photon upconversion

“…The present kinetically controlled crystallization concept for improving donor dispersibility in acceptor crystals would be widely applicable to a variety of chromophore combinations, including the recently developed precious metal-free systems 25,45,46 and NIRto-visible UC systems. [12][13][14][15]47,48 For further improvement of the current method, we consider that the key is to suppress the formation of defect sites that deactivate the triplet excitons. 28 The development of approaches to circumvent this issue is under way in our laboratory.…”

“…Consequently, the majority of TTA-UC systems have been studied in solution 8,[11][12][13][14][15] or soft polymer matrices, [16][17][18][19][20] in which the TET and TTA processes are mediated by molecular diffusion and collision. Meanwhile, it is desirable for device applications that TTA-UC processes occur in the solid state without molecular diffusion.…”

Complementary Lock‐and‐Key Ligand Binding of a Triplet Transmitter to a Nanocrystal Photosensitizer

“…[12] This shows that at least two of the bidentate ligands here outperform their monodentate congener, probably by increasing orbital overlap with the CdSe NC donor. [12] This shows that at least two of the bidentate ligands here outperform their monodentate congener, probably by increasing orbital overlap with the CdSe NC donor.…”

“…[5c] Thee xcitation density (I th )d enoting the transition from the quadratic to the linear regime for this 2,3-PyAn transmitter is 146.8 mW cm À2 for a68.7 mm solution of functionalized CdSe NCs in 2.1 mm DPAi nh exanes at room temperature.T he upconversion QYs for the other two isomers,3 ,3-PyAn and 2,2-PyAn, were 8.1 AE 0.7 %a nd 2.5 AE 0.7 %, respectively.Y anai, Kimizuka, and co-workers have shown that monodentate PyAn transmitters with just one pyridine moiety for binding to the NC result in an upconversion QY of 1.4 %. [12] This shows that at least two of the bidentate ligands here outperform their monodentate congener, probably by increasing orbital overlap with the CdSe NC donor. Although 3,3-PyAn and 2,3-PyAn have as imilar binding affinity to wurtzite CdSe NCs,t he upconversion QY of the latter is almost twice as large as that of the former.This indicates that its binding geometry matches the CdSe surface lattice best and tightly locks the anthracene core to the surface.W hile 2,2-PyAn may bind more strongly to the NCs (as indicated by ah igher number of surface-bound ligands), the upconversion QY is low,q uite close to that for the monodentate ligand.…”