Lanthanide Sensitizers for Large Anti-Stokes Shift Near-Infrared-to-Visible Triplet–Triplet Annihilation Photon Upconversion

Abstract

The upconversion of near-infrared (NIR) to visible (vis) photons is of interest for display technologies and energy conversion. Although triplet–triplet annihilation (TTA) offers a mechanism for upconversion that works efficiently at low incident irradiance flux densities, current strategies for NIR–vis upconversion based on TTA have fundamental limitations. Herein, we report a strategy for NIR–vis TTA based on lanthanide-containing complexes to sensitize the upconversion. We demonstrate a β-diketonate complex of Yb3+ paired with rubrene that emits yellow (λem = 559 nm) under NIR excitation (λexc = 980 nm). This corresponds to an exceptional anti-Stokes shift of just less than 1 eV. Thus, lanthanide complexes could unlock high-performance NIR–vis upconversion, with lanthanide sensitizers overcoming the energy loss, reabsorption, and short triplet lifetime that fundamentally limit porphyrin, nanocrystals, and direct S0–T1 sensitizers.

Triplet–triplet annihilation based near infrared to visible molecular photon upconversion

“…Upon excitation with 980 nm laser, the Yb-L/rubrene couple in deoxygenated deuterated tetrahydrofuran showed energy upconversion with DE UC = 0.95 eV (980 nm to 559 nm) and F UC of o 0.5%. 41 However, besides the advantage of clear optical window, several limitations of Yb-L sensitizer were also highlighted such as poor F UC , high excitation intensity and requirement of deuterated solvents. The deuterated solvent was required to avoid nonradiative deactivation by multiphoton relaxation via energy transfer to vibrational overtones of high-energy, highly anharmonic oscillators (mostly stretching modes of X-H moieties with X = O, N, C) in the vicinity of the metal.…”

“…The deuterated solvent was required to avoid nonradiative deactivation by multiphoton relaxation via energy transfer to vibrational overtones of high-energy, highly anharmonic oscillators (mostly stretching modes of X-H moieties with X = O, N, C) in the vicinity of the metal. 41 Even after being highly prone to photo-degradation, rubrene has been the main annihilator in most of the NIR to Vis TTA-UC systems. Kazlauskas's research group investigated the low F UC of metallophthalocyanine sensitized rubrene systems based on the subsequent energy transfer steps.…”

“…Since, Baluschev's report in 2007, 24 NIR to Vis TTA-UC systems have evolved beyond deoxygenated organic solvents to oxygen stable solid state and aqueous environments to realize practical feasibility. The evolution is accompanied by the introduction of new ISC route (direct S 0 -to-T 1 absorption), 6,23,[38][39][40] inorganicorganic hybrid systems, 12,15,[34][35][36]42 new TET route (sensitizertransmitter-annihilator, [34][35][36] sensitizer-annihilator-emitter 12,42 ), NIR harvesting beyond 950 nm, 15,34,37,41 thermally activated delayed phosphorescent sensitizer, 6 photostable annihilator, 28,29,32 s-p conjugated annihilator, 40 NIR to Vis TTA-UC MOF's, 22,23 hydrogel, 6 liquid crystals, 20 nanoparticles, 5,38,39 oxygen stable fabrication techniques, 5,6,23,26,38,39 spectral upconversion range 1140 nm to 415 nm 15,37,40 and practical applications in solar cells, 1,2 photocatalysis, 4 bioimaging 5 and optogenetics. 6 The molecular TTA-UC is cons...…”

“…Excitation spectrum of TTA-UC, laser intensity maintained at 100 W cm À2 (black line). (d) Unfiltered photograph of UC luminescence (l exc = 980 nm, 300 W cm À2) 41. Reproduced with permission from ref 41…”

Ultra-small PbS nanocrystals as sensitizers for red-to-blue triplet-fusion upconversion

“…7 Examples of sensitizers include coordination complexes, due to their strong absorption bands and high triplet yield via intersystem crossing, 6,[8][9][10][11][12][13][14][15] as well as colloidal quantum dots (QDs), [16][17][18][19][20][21][22][23] metal-halide perovskite lms and nanocrystals, [24][25][26] and materials containing lanthanide atoms. 5,27 Triplet fusion (TF) occurs when the energy from two or more triplet-excited acceptors are combined to yield a higher-energy excited state, which may generate a spin-singlet excitation capable of emitting a photon. 1,6,9,28,29 Importantly, it was recently demonstrated that triplet-fusion upconversion can enable photochemical transformations using incident long-wavelength light at low uences appropriate for tissue penetration.…”