Dmitry Busko

Photon energy upconverting nanopaper: a bioinspired oxygen protection strategy.

The development of solid materials which are able to upconvert optical radiation into photons of higher energy is attractive for many applications such as photocatalytic cells and photovoltaic devices. However, to fully exploit triplet-triplet annihilation photon energy upconversion (TTA-UC), oxygen protection is imperative because molecular oxygen is an ultimate quencher of the photon upconversion process. So far, reported solid TTA-UC materials have focused mainly on elastomeric matrices with low barrier properties because the TTA-UC efficiency generally drops significantly in glassy and semicrystalline matrices. To overcome this limit, for example, combine effective and sustainable annihilation upconversion with exhaustive oxygen protection of dyes, we prepare a sustainable solid-state-like material based on nanocellulose. Inspired by the structural buildup of leaves in Nature, we compartmentalize the dyes in the liquid core of nanocellulose-based capsules which are then further embedded in a cellulose nanofibers (NFC) matrix. Using pristine cellulose nanofibers, a sustainable and environmentally friendly functional nanomaterial with ultrahigh barrier properties is achieved. Also, an ensemble of sensitizers and emitter compounds are encapsulated, which allow harvesting of the energy of the whole deep-red sunlight region. The films demonstrate excellent lifetime in synthetic air (20.5/79.5, O2/N2)-even after 1 h operation, the intensity of the TTA-UC signal decreased only 7.8% for the film with 8.8 μm thick NFC coating. The lifetime can be further modulated by the thickness of the protective NFC coating. For comparison, the lifetime of TTA-UC in liquids exposed to air is on the level of seconds to minutes due to fast oxygen quenching.

Micellar carrier for triplet–triplet annihilation-assisted photon energy upconversion in a water environment

In this paper, we demonstrate energetically conjoined triplet?triplet annihilation-assisted photon energy upconversion (UC) operating in an aqueous environment. Obtained micellar structures show very efficient UC emission in a water environment under extremely low excitation light intensity, down to 10?mW?cm?2. The demonstrated sub-linear intensity dependence of the UC emission is of crucial importance for life science applications, allowing upconverted photons to be generated even at low intensity that then serve as a local, in situ, optical excitation source for subsequent light-triggered processes.

Triplet-Triplet Annihilation Upconversion Based Nanocapsules for Bioimaging Under Excitation by Red and Deep-Red Light

Non-toxic and biocompatible triplet-triplet annihilation upconversion based nanocapsules (size less than 225 nm) were successfully fabricated by the combination of miniemulsion and solvent evaporation techniques. A first type of nanocapsules displays an upconversion spectrum characterized by the maximum of emission at λmax = 550 nm under illumination by red light, λexc = 633 nm. The second type of nanocapsules fluoresces at λmax = 555 nm when excited with deep-red light, λexc = 708 nm. Conventional confocal laser scanning microscopy (CLSM) and flow cytometry were applied to determine uptake and toxicity of the nanocapsules for various (mesenchymal stem and HeLa) cells. Red light (λexc = 633 nm) with extremely low optical power (less than 0.3 μW) or deep-red light (λexc = 708 nm) was used in CLSM experiments to generate green upconversion fluorescence. The cell images obtained with upconversion excitation demonstrate order of magnitude better signal to background ratio than the cell images obtained with direct excitation of the same fluorescence marker.

Synergetic effect in triplet-triplet annihilation upconversion: highly efficient multi-chromophore emitter.

In the context of photonic applications using sunlight, specialattention is deservedly paid to organic multicomponent up-conversion (UC) systems comprised of an emitter (such as con-jugated semiconductor polymers or aromatic hydrocarbon de-rivatives) and a sensitizer part (such as metallated macrocy-cles).

Photon Upconversion at Crystalline Organic-Organic Heterojunctions

Triplet transfer across a surface-anchored metal-organic-framework heterojunction is demonstrated by the observation of triplet-triplet annihilation photon -upconversion in a sensitizer-emitter heterostructure. Upconversion thresholds under 1 mW cm-2 are achieved. In the broader context, the double-electron-exchange mechanism of triplet transfer indicates that the heterojunction quality is sufficient for electrons to move between layers in this solution-processed crystalline heterostructure.

Reversible oxygen addition on a triplet sensitizer molecule: protection from excited state depopulation†

We demonstrate that photoactivated oxygen addition to diphenylanthracene moities can be used as a tool for protection of porphyrins phosphorescence against oxygen quenching. Phosphorescent palladium(II) tetrabenzoporphyrin, covalently linked to four diphenylanthracene moieties, was synthesized and studied. Upon irradiation with ambient light or red laser in solution in air, addition of oxygen and formation of the corresponding endoperoxides were observed. Heating of the irradiated samples afforded the parent porphyrin material.

Synthesis of Triplet-Triplet Annihilation Upconversion Nanocapsules Under Protective Conditions

Triplet-triplet annihilation upconversion (TTA-UC) nanocapsules are synthesized under oxygen-protective conditions (i.e., complete darkness and argon atmosphere) by free-radical miniemulsion polymerization. These conditions help to exclude the oxidation of the emitter molecules caused by singlet oxygen, generated during the synthesis at daylight conditions and oxygen-rich environment. Subsequently, keeping all the other experimental conditions the same, samples synthesized at protective conditions demonstrate substantially increased UC efficiency. These experimental facts strongly support the hypothesis that posterior removing of oxygen from TTA-UC nanocapsules is not sufficient to obtain reproducible and sustainable UC results. The schematic representation shows the influence of sunlight on the formation of singlet oxygen and its effect on the triplet-triplet annihilation upconversion process.

Finely-tuned NIR-to-visible up-conversion in La2O3:Yb3+,Er3+ microcrystals with high quantum yield

Up-conversion (UC) materials whose emission color can be finely-tuned while a high UC quantum efficiency is maintained are desirable for many applications. Herein, we report near-infrared-to-visible La2O3:Yb3+,Er3+ (LYE) UC materials with a high internal quantum yield (UCQY) of 3.8%, external UCQY (brightness) of 1.6% and tunable emission color. UC emission colors from pure green to reddish-orange can be precisely tailored by simply controlling synthesis conditions, whilst maintaining the high UCQY. The internal UCQY and external UCQY of LYE yield better performance than both commercially available and other record UC phosphors reported in the literature under the same excitation conditions. The facile preparation combined with the color-tuning and high UCQYs make these materials attractive candidates for solar energy harvesting, sensors, 3D volumetric displays, solid state lasers and bio-imaging.

Monodisperse β-NaYF4:Yb3+,Tm3+ hexagonal microplates with efficient NIR-to-NIR up-conversion emission developed via ion exchange

Monodisperse β-NaYF4:Yb3+,Tm3+ (NYF) hexagonal microplates with efficient near-infrared (NIR)-to-NIR up-conversion (UC) developed via a new ion-exchange modified hydrothermal method are reported. Ion exchange modification (IEM) not only significantly increases the UC intensity by up to 1000 times and prolongs the emission lifetimes of Tm3+ and Yb3+, but also enables the monodisperse morphology and size of hexagonal microplates to be maintained. A high UC quantum efficiency (QE) of 3.1% is obtained for IEM β-NaYF4:20%Yb3+,1%Tm3+ when excited with 980 nm light at a power density of 10 W cm−2. The UC emission properties can be finely tailored by changing the NaF/NYF molar ratio (NYF represents lanthanide doped β-NaYF4) and the doping concentration of Tm3+. The two photon NIR UC emission centered at ∼803 nm (arising from Tm3+: 3H4 → 3H6) dominates the UC emission spectrum and high concentrations of Tm3+ favor NIR UC further. A proof-of-concept optical image of printed patterns is demonstrated to verify their applications in security. These results suggest the promising applications of the newly developed monodisperse β-NaYF4:Yb3+,Tm3+ hexagonal microplates in security, luminescent labels, solid-state lasers, amplifiers, and biomedicine.

Room-Temperature High-Efficiency Solid-State Triplet–Triplet Annihilation Up-Conversion in Amorphous Poly(olefin sulfone)s

Triplet-triplet annihilation up-conversion (TTA-UC) is a developing technology that can enable spectral conversion under sunlight. Previously, it was found that efficient TTA-UC can be realized in polymer hosts for temperatures above the polymers glass transition (T > Tg). In contrast, TTA-UC with high quantum yield for temperatures below Tg is rarely reported. In this article, we report new polymer hosts in which efficient TTA-UC is observed well below Tg, when the polymer is in a fully solid state. The four poly(olefin sulfone) hosts were loaded with upconversion dyes, and absolute quantum yields of TTA-UC (ηTTA-UC) were measured. The highest value of ηTTA-UC = 2.1% was measured for poly(1-dodecene sulfone). Importantly, this value was the same in vacuum and at ambient conditions, indicating that the host material acts as a good oxygen barrier. We performed time-resolved luminescence experiments in order to elucidate the impact of elementary steps of TTA-UC. In addition to optical characterization, we used magic angle spinning solid-state NMR experiments to estimate the T2 transverse relaxation time. Relatively long T2 times measured for poly(olefin sulfone)s indicate an enhanced nanoscale fluidity in the studied (co)polymers, which unexpectedly coexists with a rigidity on the macroscale. This would explain the exceptional triplet energy transfer between the guest molecules, despite the macroscopic rigidity.