Highly Improved Quantum Efficiency in Blend Polymer LEDs

Kang, In‐Nam; Hwang, Do‐Hoon; Shim, Hong‐Ku; Zyung, Taehyoung; Kim, Jang‐Joo

doi:10.1021/ma950858m

Cited by 96 publications

(66 citation statements)

References 26 publications

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“…[23] Therefore, the results indicate that the PTCD derivatives studied here are promising materials for photonic devices based on 2PA processes, such as optical limiters and 2PP lasers. The monotonic increase observed in the 2PA cross-section spectra at wavelengths below 800 nm can be attributed to the resonance enhancement of the nonlinearity, in agreement with the resonant denominator in the sum-over-states (SOS) model, [11,31,32] assuming that the p ® p* transition (corresponding to the peak of the absorption band around 550 nm) provides the major contribution to the virtual intermediate state and that the excited state corresponds to the absorption peaks around 350 nm. Regarding the molecular strategy to obtain materials with efficient twophoton cross-sections, our results suggest that even larger 2PA cross-sections could possibly be obtained by manipulating the perylene derivatives, by positioning donor or acceptor groups symmetrically, or by increasing the molecule conjugation length, in agreement with molecular design strategies proposed in the literature.…”

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confidence: 61%

Perylene Derivatives with Large Two‐Photon‐Absorption Cross‐Sections for Application in Optical Limiting and Upconversion Lasing

et al. 2005

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We report on the degenerate two-photon absorption (2PA) spectra of perylene tetracarboxylic derivatives (PTCDs), bis-(benzimidazo)perylene (AzoPTCD), and bis(benzimidazo)-thioperylene (Monothio BZP), obtained by means of the Z-scan technique with femtosecond laser pulses. The results show that these materials possess exceptionally high 2PA cross-sections. At 750 nm, for instance, AzoPTCD and Monothio BZP present 2PA cross-sections of 3400 10 ±50 cm 4 s photon ±1 and 1170 10 ±50 cm 4 s photon ±1, respectively. In addition, the 2PA saturation behavior observed as the laser irradiance increases and the strong two-photon-induced fluorescence suggest that PTCD compounds may be attractive candidates for applications in optical limiting and two-photon pumped (2PP) upconversion lasing.Upon exposure to intense laser pulses, molecules can instantaneously absorb two photons to access an excited state, each of them with half of the energy required to match the electronic transition. Such a 2PA process has interesting characteristics with direct consequences to applications including: i) improved spatial resolution owing to the square dependence on the excitation irradiance; ii) negligible linear absorption at the pumping wavelength, with a resulting increase of penetration depth, particularly in biological tissues; and iii) very fast temporal response. The advantages of the 2PA mechanism have been explored in numerous studies leading to promising applications, such as 2PP frequencyupconverted lasing, optical limiting, fluorescence excitation microscopy and imaging, three-dimensional optical data storage and lithographic microfabrication, and photodynamic therapy.[1±8] Accordingly, a great deal of effort has been directed to the development of various design strategies to synthesize new two-photon absorbing materials with large 2PA cross-sections (d) and to increase physical and chemical stabilities. Most of the recently developed two-photon absorbers are organic compounds. [2,5,9±15] Here, we investigate the possibility of using PTCD dyes as materials with high nonlinear optical absorption. PTCDs are organic dyes, readily available and thermally and chemically stable. The perylene moiety presents remarkable electron-donor characteristics, [16,17] although on adding lateral groups, the molecule can play either an electron-acceptor or -donor role. Moreover, their strong absorption and emission in the visible spectral range makes them potential candidates for applications as organic semiconductors, photoconductors, and laser materials.[16±22]Although high optical nonlinearities have been reported in organic materials at specific wavelengths, only recently has the dispersion of the nonlinear absorption over a wide spectral range begun to be characterized. [2,5,7,13±15,23±26] From an applications point of view, such information is important in formulating a molecular design strategy for a given nonlinear optical material. In this context, the present work reports on the degenerate 2PA cross-section spectra of AzoPTCD and Monot...

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confidence: 61%

Perylene Derivatives with Large Two‐Photon‐Absorption Cross‐Sections for Application in Optical Limiting and Upconversion Lasing

et al. 2005

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“…Organic light-emitting devices (OLEDs) containing a blend of poly[2-(2-ethylhexyloxy)-5-methoxy-1, 4-phenylenevinylene] (MEH-PPV) and an electron transporting material, 2,7-bis[2-(4-tert-butylphenyl)-1,3,4-oxadiazol-5-yl]-9,9-dihexylfluorene have been fabricated. The external quantum efficiencies of the OLEDs containing the electron transport compound were increased significantly over those obtained for devices based only on MEH-PPV.…”

Section: (Received 4 September 2003; Accepted 3 June 2004)mentioning

confidence: 99%

“…As the polymer molecules become separated by the electron transporting molecules, concentration quenchingintermolecular nonradiative decay of singlet excitons-will be reduced resulting in an enhanced light output. Kang et al 4 previously noted that the external quantum efficiency increased over seven times when MEH-PPV was blended with 90 wt% poly(methyl methacrylate), an electro-optically inert material. However, a much larger increase in efficiency (almost 500 times) was noted by mixing the MEH-PPV with another electroactive polymer.…”

Section: (Received 4 September 2003; Accepted 3 June 2004)mentioning

confidence: 99%

Organic light-emitting diodes based on a blend of poly[2-(2-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene] and an electron transporting material

Ahn

Wang

Pearson

et al. 2004

Applied Physics Letters

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“…5, in which the black line represents the absorption spectrum for a sample that was not micromachined. As it can be seen, the absorption band centered at 500 nm ( → * electronic transition of MEH-PPV [30,31]) decreases with the energy of the pulse used in the micromachining [14], indicating a photobleaching of the sample upon fs-laser exposure [32,33]. Such changes in the MEH-PPV absorption spectrum have been attributed to photo-oxidation [6].…”

Section: Resultsmentioning

confidence: 95%