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RISS 인기검색어
- 검색키워드
- 저자 : Podzorov Vitaly (검색결과 2 건)
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Photon Upconversion in Crystalline Rubrene: Resonant Enhancement by an Interband State
Cruz, Chad D.,Choi, Hyun Ho,Podzorov, Vitaly,Chronister, Eric L.,Bardeen, Christopher J. American Chemical Society 2018 The Journal of Physical Chemistry Part C Vol.122 No.31
<P>Triplet-triplet exciton annihilation after sensitization of the triplet states by a near-infrared (NIR)-absorbing sensitizer enables rubrene to function as a photon upconversion (UC) material. In this paper, we demonstrate an alternate pathway to NIR upconversion in pristine rubrene crystals: resonantly enhanced two-photon absorption via a weakly allowed interband state. We find that all crystalline rubrene samples exhibit NIR-to-visible upconversion that can be easily observed by eye under low-intensity (20 W/cm<SUP>2</SUP>) continuous wave excitation. The amount of continuous wave photoluminescence (PL) is comparable to what is observed under femtosecond pulsed excitation with the same average intensity. A wide range of excitation intensities (<I>I</I>) for the PL power dependence are explored and careful fitting of the intensity dependence of the upconverted PL shows that it has an approximate <I>I</I><SUP>4</SUP> → <I>I</I><SUP>2</SUP> transition. Moreover, there is a pronounced dependence of the per-pulse upconverted PL signal on the laser repetition rate. A four-state kinetic model with a long-lived (∼1 μs) interband state that takes into account fission and fusion dynamics can reproduce both the <I>I</I><SUP>4</SUP> → <I>I</I><SUP>2</SUP> transition and the dependence of the PL on pulse repetition rate. The modeling suggests that this interband state arises from a low-concentration species, possibly a crystal defect or defective rubrene molecules. Several other polyacene crystals (tetracene, diphenylhexatriene, and perylene) measured under the same conditions did not exhibit similar behavior. The observation of resonantly enhanced upconverted PL without the addition of chemically distinct sensitizers suggests that interband states in organic molecular crystals can generate new and possibly useful photophysical behavior.</P> [FIG OMISSION]</BR>
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Choi, Hyun Ho,Najafov, Hikmet,Kharlamov, Nikolai,Kuznetsov, Denis V.,Didenko, Sergei I.,Cho, Kilwon,Briseno, Alejandro L.,Podzorov, Vitaly American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.39
<P>Photoinduced charge transfer between semiconductors and gate dielectrics can occur in organic field-effect transistors (OFETs) operating under illumination, leading to a pronounced bias-stress effect in devices that are normally stable while operating in the dark. Here, we report an observation of a'polarization-dependent photoinduced bias-stress effect in two' prototypical single-crystal OFETs, based on rubrene and tetraphenylbis(indolo{l,2-alpha})quinolin. We find that the decay rate of the source-drain current in these OFETs under, illumination is a periodic function of the polarization angle of incident photoexcitation with respect to the crystal axes, with a periodicity of n. The angular positions of maxima and minima of the bias-stress rate match those of the optical absorption coefficient of the corresponding crystals. The analysis of the effect shows that it stems from a charge transfer of 'hot' holes, photogenerated in the crystal within a very short thermafization length (MLT mu m) from the semiconductor-dielectric interface. The observed phenomenon is a type of intrinsic structure-property relationship, revealing how molecular packing affects parameter drift in organic transistors under illumination. We also demonstrate that a photoinduced charge transfer in OFETs can be used for recording rewritable accumulation channels with an optically defined geometry and resolution, which can be used in a number of potential applications.</P>
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