Vladimir Yakutkin

Upconversion with ultrabroad excitation band: Simultaneous use of two sensitizers

The authors demonstrate the ability to combine sensitizers effectively working with single emitter in order to increase the excitation window for noncoherent upconversion. They show effective upconversion of the red part of the sun spectrum realized by ultralow excitation intensity (as low as 1Wcm−2) and ultrabroad excitation spectrum (Δλ∼80nm).

Towards the IR Limit of the Triplet-Triplet Annihilation-Supported Up-Conversion: Tetraanthraporphyrin

The processes by which locally (or in situ) up-converted photons are generated by NIR or IR excitation sources have been very intensively studied and have remarkable application potential in fields like up-conversion displays, biological imaging and sensing, and photodynamic therapy of cancer. The blue-shifted emission generated in the known and long-time studied up-conversion processes results from either two-photon absorption (TPA) in organic molecules, quantum dots or in proximity of metallic clusters, or sequential energy transfer (ETU) in rare-earth ion-doped glasses. All these processes have a common characteristic: they need an excitation source with very high brightness—in the case of TPA-based processes because of the virtual energy level used, in the case of the ETU-based processes because of the finite width of the ionic energy levels used. Additionally, both these processes need moderate or strong optical pumping, normally in order of many kWcm 2 up to MWcm . Recently, a different approach for up-conversion (UC), based on energetically conjoined triplet–triplet annihilation (TTA) was demonstrated. The fundamental advantage of the TTA-supported UC is its inherent independence on the coherence of the excitation light. The TTA-supported UC resolves also another demanding limitation of the above described “conventional” methods for UC (e.g., the ETU and all types of TPA)—the necessity to excite the samples with extremely bright optical sources (e.g., lasers). In contrast, for excitation of an efficient TTA–UC, optical sources with spectral power density of 125 mWnm 1 are sufficient and, in particular, the excitation source can be the Sun. The next advantage revealing the enormous application potential of the energetically conjoined TTA–UC is the very low intensity needed (on the order of 100 mWcm ) to achieve high quantum yields, on the order of 2–4% in organic solutions. In a further step, the efficiency of the TTA–UC in bulk solid-state films, composed of the sensitizer and emitter molecules blended in inactive polymer matrix, has to be optimized as it is significantly lower than in solutions. The TTA-supported up-conversion devices, based on organic solutions are very efficient, but cannot be easily sealed for the long term. The solid-state devices of this kind can be sealed easily, but they are not efficient enough. This obstacle can be avoided when highly viscous matrices are used. In fact, the energetically conjoined TTA–UC in highly viscous matrices possesses all the required characteristics: high quantum yield (comparable with those in liquid organic solution of the active species), very low excitation intensity ( 25 mWcm ), extremely low spectral power density optical sources ( 200 mWnm ), and versatility in excitation and emission wavelengths. These devices can be also sealed easily. The combination of all these unique characteristics and possibilities make energetically conjoined TTA–UC ready for diverse applications, such as all-organic, flexible, and transparent displays, up-converter devices for increasing the efficiency of, for example, dye-sensitized solar cells and local, in situ, generator of blue-shifted photons. To explore the above describe applications in their full, the IR limit, that is, the lowest energy photons able to serve as pumping source for the studied energetically conjoined TTA is of crucial importance. The highest excitation wave[a] Dr. V. Yakutkin, Dr. S. Baluschev Max-Planck-Institute for Polymer Research Ackermannweg 10, 55128 Mainz (Germany) Fax: (+49)6131-379-100 E-mail : balouche@mpip-mainz.mpg.de [b] S. Aleshchenkov, S. Chernov, Dr. A. Cheprakov Department of Chemistry, Moscow State University 119899 Moscow (Russia) Fax: (+7)495-939-1854 E-mail : avchep@elorg.chem.msu.ru [c] Dr. T. Miteva, Dr. G. Nelles Sony Deutschland GmbH Materials Science Laboratory, Hedelfingerstr. 61 70327 Stuttgart (Germany) Fax: (+49)711-5858-484 E-mail : miteva@sony.de Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200801305.

Two pathways for photon upconversion in model organic compound systems

We have studied the phenomenon of photon upconversion in systems of two model compounds as highly efficient blue emitters sensitized with metallated macrocycle molecules in thin films. The bimolecular upconversion process in these systems is based on the presence of a metastable triplet excited state of the macrocycles giving rise to dramatically different photophysical characteristics relative to the other known methods for photon upconversion such as two-photon absorption, parametric processes, second harmonic generation, and sequential multiphoton absorption. The chosen blue emitter molecules have suitably positioned triplet levels: in the case of an oligofluorine—essentially higher and in the case of diphenylanthracene—lower than the sensitizer porphyrin platinum triplet level and thus two excitation pathways for photon upconversion were observed and investigated.

Annihilation assisted upconversion: all-organic, flexible and transparent multicolour display

In this paper, we demonstrate the first all-organic, transparent, flexible, versatile colour displays based upon triplet-triplet annihilation assisted photon energy upconversion in viscous polymeric matrix. The devices work with ultra-low excitation intensities down to 20mWcm 2 red or near-IR light. The displays are based on metallated-porphyrin sensitizers in combination with emitters dispersed in a transparent polymeric matrix and are driven by galvo- scanned laser diodes. The displays have external quantum yield as high as 3.2%. The response time can be adjusted to specific application requirements—up to 80µs allowing kHz-refreshment rate of the displayed information. It is possible to easily tune the optical density of the screens in order to obtain a desired transmittance for the excitation beam. We demonstrate the ability to achieve multicolour emission, using only one excitation source. There are practically no display size limitations.

Investigation of Oxygen Permeation through Composites of PMMA and Surface-Modified ZnO Nanoparticles.

Oxygen permeabilities of nanocomposite films consisting of poly(methyl methacrylate) (PMMA) and different amounts of spherical zinc oxide (ZnO) nanoparticles were determined to investigate the barrier effect of this material with respect to particle content. A method was applied which is based on quenching of an excited phosphorescent dye by oxygen. Possible effects of the nanoparticles on the response of the dye molecules were investigated and were ruled out.

Response to "Comment on 'Two pathways for photon upconversion in model organic compound systems' [J. Appl. Phys. 101, 023101 (2007)]"

We have studied the phenomenon of photon upconversion in systems of two model compounds as highly efficient blue emitters sensitized with metallated macrocycle molecules in thin films. Aggregation between the active molecules (metallated porphyrins and anthracene derivatives) indeed plays a very important role in the triplet-triplet annihilation supported photon upconversion process. Contrary to the suggestions of Steer [J. Appl. Phys. 102, 076102 (2007)] aggregation (followed from phase separation) is a highly undesired effect: external quantum yields of the level of 1%–3% are observed only in systems with a low degree of aggregation (solutions), whereas the solid state films exhibit at least order of magnitude lower upconversion quantum yield than solutions. Additionally, the “only excitons in aggregates model” cannot explain the increase of the linear absorption of the sensitizer at the presence of the emitter. Furthermore, this hypothesis cannot explain why the upconversion quantum yield increases whe...

44.5L: Late-News Paper: All-organic, Transparent Up-conversion Displays with Tailored Excitation and Emission Wavelengths

In this paper we describe the Worlds first all-organic, transparent, flexible, versatile color displays based upon triplet-triplet annihilation assisted photon up-conversion. The devices work with ultra-low excitation intensities down to 10 mWcm−2 red/near-IR light. The displays are based on metallated-porphyrin sensitizers in combination with emitters in a transparent matrix and are driven by galvano-scanned laser diodes. The displays have external quantum yield as high as 3.2%. The response time can be adjusted to specific application requirements — from a few μs to few 100 μs allowing kHz-refreshment rate of the displayed information. It is possible to easily tune the optical density of the screens in order to obtain a desired transmittance for the excitation beam. We demonstrate the ability to achieve multicolor emission, using only one excitation source. There are practically no display size limitations and it is a very simple, cost-effective fabrication.