Co-reporter:Wenyu Ji, Shihao Liu, Han Zhang, Rong Wang, Wenfa Xie, and Hanzhuang Zhang
ACS Photonics May 17, 2017 Volume 4(Issue 5) pp:1271-1271
Publication Date(Web):April 4, 2017
DOI:10.1021/acsphotonics.7b00216
All-inorganic and low-cost quantum-dot light-emitting diodes (QLEDs) are always desired considering the easy processing and outstanding physical and chemical stability of inorganic oxides. Herein, efficient all-inorganic QLEDs are demonstrated by using NiO and ZnO as the charge transport layers fabricated via ultrasonic spray processes. Excellent device performance is achieved thanks to the introduction of an Al2O3 interlayer between quantum dots (QDs) and an amorphous NiO layer. Transient photoluminescence and electricity measurements indicate that the Al2O3 layer can suppress the exciton quenching induced by the NiO layer and reduce the electron leakage from QDs to NiO. In consequence, relative to that of a device without an Al2O3 layer, the efficiency of an Al2O3-containing device is enhanced by a factor of 539%, increasing from 3.8 cd/A to 20.5 cd/A, and it exhibits color-saturated green emission (peak at 530 nm) and high luminescence (>20 000 cd/m2). These are the best performances for all-inorganic QLEDs reported to date. Meanwhile, it is demonstrated that ultrasonic spray is a feasible and cost-effective technology to construct efficient all-inorganic QLEDs. We anticipate that these results will spur the progress toward realization of high performance and mass production of all-inorganic QLEDs as a platform for QD-based full-color displays.Keywords: exciton quenching; inorganic metal oxides; insulating layer; passivation; quantum-dot light-emitting diodes (QLEDs);
Co-reporter:Lu Zou, Ying-Hui Wang, Ning Sui, Wen-Yu Ji, Ming-Rui Tan, Mou-Cui Ni, Han-Zhuang Zhang
Journal of Luminescence 2017 Volume 190(Volume 190) pp:
Publication Date(Web):1 October 2017
DOI:10.1016/j.jlumin.2017.05.040
We introduce the preparation process of two-dimensional coumarin 6 (C-6) doped poly-methyl-methacrylate (PMMA) photonic crystals (2D C-6 PCs) in detail. We also cover the 2D C-6 PC with translucent Ag shells. By analyzing the system of 2D C-6 PCs and hemispherical Ag shells, we find that resonance energy transfer and local surface plasmon resonance (LSPR) can affect the photoluminescence (PL) characteristics of 2D C-6 PCs. When we cover the 2D C-6 PC with translucent Ag shell, there is energy transfer between the 2D C-6 PCS and the hemispherical Ag shells. The data of photoluminescence and the corresponding decay curves reveal that resonance energy transfer and localized surface plasmon resonance could effectively manipulate the PL properties of 2D C-6 PCs.
Co-reporter:Xiao-Chun Chi, Mou-Cui Ni, Ying-Hui Wang, Ning Sui, Wen-Yan Wang, Ran Lu, Yan-Qiang Yang, Wen-Yu Ji, Han-Zhuang Zhang
Journal of Photochemistry and Photobiology A: Chemistry 2017 Volume 346(Volume 346) pp:
Publication Date(Web):1 September 2017
DOI:10.1016/j.jphotochem.2017.06.008
•Pull-push chromophores are comprised of TPA andβ-diketones difluorboron complexes.•The increasing of electron-acceptor improves the PL intensity of compounds.•The photo-excitation dynamics was measured by ultrafast TA spectroscopy.•Three electron-acceptor prolongs the ICT process.Two push-pull compounds, which are comprised of triphenylamine (TPA) (electron donor units) and functionalized β-diketones difluorboron complexes (electron acceptor units) are probed by many spectroscopies, which offers the relationship between electron acceptor and the intrinsic excited state properties of push–pull chromophores. We found that the photoluminescence (PL) intensity would enhance with the number of electron acceptor. Transient absorption (TA) data shows that intramolecular charge transfer (ICT) process really exists in the two molecules after photoexcitation and this process would be prolonged through increasing the electron-acceptor, which would be responsible for the improvement of PL property.Download high-res image (130KB)Download full-size image
Co-reporter:Wenyu Ji;Ting Wang;Bingyan Zhu;Han Zhang;Rong Wang;Dandan Zhang;Liezun Chen;Qingyi Yang;Hanzhuang Zhang
Journal of Materials Chemistry C 2017 vol. 5(Issue 18) pp:4543-4548
Publication Date(Web):2017/05/11
DOI:10.1039/C7TC00514H
Flexible quantum dot light emitting diodes (QLEDs) are highly desired due to their advantages of foldability, lightweight, and potential applications in lighting and displays. In this report, we successfully fabricated high performance red (R), green (G), and blue (B) three primary color QLEDs based on a poly(ethylene-terephthalate)/ITO/Ag/ITO (PET–IAI) cathode. The multilayer flexible IAI electrode shows outstanding stability even after bending over 2000 times with a critical bending radius of 5 mm; the sheet resistance of the IAI film only increases from 12.7 to 14.8 Ω □−1. The maximum current efficiencies are 16.3, 86.5, and 16.1 cd A−1 for RGB QLEDs, respectively, which is the best device performance for flexible RGB QLEDs reported to date. Moreover, to the best of our knowledge, these are also record efficiencies for the green and blue devices in all the reported QLEDs. Furthermore, all the devices show saturated electroluminescence (EL) with the corresponding emission peaks at 606, 530, and 478 nm for three primary color QLEDs. The superior performance is a result of high transmittance and stability of the PET–IAI film. These results signify remarkable progress in flexible QLEDs and suggest that the PET–IAI based flexible QLEDs can offer a practicable platform for foldable applications.
Co-reporter:Han Zhang, Ning Sui, Xiaochun Chi, Yinghui Wang, Qinghui Liu, Hanzhuang Zhang, and Wenyu Ji
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 45) pp:31385
Publication Date(Web):October 26, 2016
DOI:10.1021/acsami.6b09246
A study of hybrid inverted quantum-dot (QD) light-emitting diodes constructed with and without Al2O3 interlayers is presented. The Al2O3 interlayers are deposited at ZnO/QDs or/and QDs/4,4′-bis(carbazol-9-yl)biphenyl interfaces, resulting in large improvement of device performance, including luminance, current efficiency, and device lifetime. Especially, the devices with QD emitters sandwiched by two Al2O3 layers exhibits outstanding performance, the longest operation lifetime, and mediate efficiency. The maximum current efficiency of 15.3 cd/A is obtained, an enhancement factor of 35% in comparison to that (11.3 cd/A) of conventional device without Al2O3 layer. Moreover, device lifetime is also largely enhanced, over 110 000 h for the device containing two Al2O3 interlayers, nearly 40% enhancement relative to that of conventional device that shows a lifetime of only 80 000 h. On the basis of electrical property and photoluminescence spectroscopy studies, we demonstrate that the Al2O3 interlayers play crucial roles in suppressing the leakage current across the device and reducing exciton quenching induced by ZnO.Keywords: exciton quenching; insulating layer; leakage current; QLED; quantum dot
Co-reporter:Wen-Chao Bai, Zhong-Jian Lan, Han-Zhuang Zhang, Han Zhang, Li Jiang
Superlattices and Microstructures 2016 Volume 97() pp:167-175
Publication Date(Web):September 2016
DOI:10.1016/j.spmi.2016.06.026
•We propose the phonon-polariton mode of in Czochralski-grown piezoelectric superlattice.•The mechanism for polariton coupling is analyzed.•We discuss the factors that influence the properties of the phonon–polariton.•Some potential applications are discussed.The properties of phonon-polaritons in Czochralski-grown piezoelectric superlattice (CPSL), are studied theoretically. We propose the phonon-polariton mode of CPSL. The mechanism for polariton coupling is analyzed. We discuss the factors that influence the properties of the phonon-polariton. Some potential applications are also discussed.
Co-reporter:Peng Yang;Yingshu Yang;Yinghui Wang;Jiechao Gao;Ning Sui;Xiaochun Chi;Lu Zou
Luminescence 2016 Volume 31( Issue 1) pp:4-7
Publication Date(Web):
DOI:10.1002/bio.3000
Abstract
The photoluminescence (PL) characteristics of CdSe quantum dots (QDs) infiltrated into inverse opal SiO2 photonic crystals (PCs) are systemically studied. The special porous structure of inverse opal PCs enhanced the thermal exchange rate between the CdSe QDs and their surrounding environment. Finally, inverse opal SiO2 PCs suppressed the nonlinear PL enhancement of CdSe QDs in PCs excited by a continuum laser and effectively modulated the PL characteristics of CdSe QDs in PCs at high temperatures in comparison with that of CdSe QDs out of PCs. The final results are of benefit in further understanding the role of inverse opal PCs on the PL characteristics of QDs. Copyright © 2015 John Wiley & Sons, Ltd.
Co-reporter:Wenyu Ji, Ying Lv, Pengtao Jing, Han Zhang, Jia Wang, Hanzhuang Zhang, and Jialong Zhao
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 29) pp:15955
Publication Date(Web):July 3, 2015
DOI:10.1021/acsami.5b04050
Highly efficient red quantum dot light-emitting diodes (QD-LEDs) with a very high current efficiency of 16 cd/A were demonstrated by adopting stepwise hole-transport layers (HTLs) consisting of 4,4′-N,N′-dicarbazole-biphenyl (CBP) combined with N,N′-dicarbazolyl-3,5-benzene (mCP). The mCP layer plays two important roles in this kind of QD-LEDs. One is that it can block the electron to leak into the HTL due to its higher LUMO (LUMO = the lowest unoccupied molecular orbital) energy level than that of CBP; and the other is it can separate the carrier accumulation zone from the exciton formation interface, which is attributed to the stepwise hole-transport layer structure. Moreover, the lower HOMO (HOMO = the highest occupied molecular orbital) energy level of mCP decreases the hole-injection barrier from the HTL to the QD emitting layer, which improves the charge carrier balance injected into the QD layer, reducing the turn-on voltage of QD-LEDs fabricated with the stepwise HTL structure.Keywords: charge accumulation; leakage current; light emitting diodes; quantum dots; stepwise hole-injection layer;
Co-reporter:Jia Wang, Han Zhang, Wenyu Ji, Hanzhuang Zhang
Synthetic Metals 2015 Volume 209() pp:484-489
Publication Date(Web):November 2015
DOI:10.1016/j.synthmet.2015.08.033
•The ethanol treated PEDOT:PSS is used in QD-LEDs.•The overall performance of PEDOT:PSS is enhanced with ethanol treated PEDOT:PSS as the HIL.•AFM measurements indicate the conductivity of ethanol treated PEDOT:PSS films is improved.The conductivity of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) film is improved by simply mixing PEDOT:PSS solution with ethanol for the film deposition, and the performance of quantum-dot light-emitting diodes (QD-LEDs) is significantly enhanced with ethanol treated (ET- treated) PEDOT:PSS as the hole injection layer (HIL). Comparing with the pristine PEDOT:PSS based device, the current density of device with ET-treated PEDOT:PSS as the HIL is increased by 18%, from 50 to 59 mA/cm2, at operating voltage of 5 V, and the maximum current efficiency is enhanced by 12.5%, from 10.4 to 11.7 cd/A, which is due to the improved conductivity of ET-treated PEDOT:PSS film. With atomic force microscopy (AFM) measurements, we demonstrate that the improvement of the conductivity of PEDOT:PSS film is due to the decreased PSSH amount after solvent treatment, reducing the thickness of PSSH insulating shell, leading to an efficient charge transport across the PEDOT chains.
Co-reporter:Xiao-Chun Chi, Ying-Shu Yang, Ying-Hui Wang, Jie-Chao Gao, Ning Sui, Hai-Gui Yang, Lu Zou, Zhi-Hui Kang, Han-Zhuang Zhang
Optical Materials 2015 Volume 46() pp:350-354
Publication Date(Web):August 2015
DOI:10.1016/j.optmat.2015.04.043
•The periodic porous structure of TiO2 inverse opal PCs is manifest by SEM image and XRD pattern.•The TiO2 inverse opal PCs manipulate the PL characteristics of CdTe/ZnS QDs.•The TiO2 inverse opal PCs suppress the PL enhancement nonlinearity of CdTe/ZnS QDs.The photoluminescence (PL) characteristics of CdTe/ZnS quantum dots (QDs) infiltrated in TiO2 inverse opal photonic crystals (PCs) are studied in detail. The PL dynamics of QDs show that the PCs could accelerate the PL relaxation rate of QDs as the PL peak of QDs is overlapped with the photonic stop band of PCs. Besides, the PCs could decrease the activation energy of QDs due to its porous structure and suppress the exciton annihilation process of QDs at high excitation intensity, owing to the light scattering effect. The final results are beneficial for people in further understanding the role of inverse opal PCs on manipulating the PL characteristics of QDs.
Co-reporter:Lu Zou, Ning Sui, Ying-Hui Wang, Cheng Qian, Yu-Guang Ma, Han-Zhuang Zhang
Journal of Luminescence 2015 158() pp: 281-285
Publication Date(Web):
DOI:10.1016/j.jlumin.2014.10.016
Co-reporter:Fu-yin Wang, Ying-hui Wang, Ning Sui, Yun-fei Song, Yu-guang Ma and Han-zhuang Zhang
New Journal of Chemistry 2014 vol. 38(Issue 8) pp:3885-3888
Publication Date(Web):07 May 2014
DOI:10.1039/C3NJ01587D
We prepared quantum dots (QDs) based on a conjugated molecule (coumarin 6, C-6), which is considered to be a mesoscopic aggregate, to build a bridge linking the monodisperse state (solution state) and macroscopic aggregates (powder state). Their spectral features, including steady spectral data, dynamic features and fluorescence quantum yields, have been compared in detail. All dynamic data were modelled using the continuous rate distribution function. The final results showed that the fluorescence quantum yield of organic quantum dots based on C-6 gradually decreases as the size of the QDs increases, which may be attributed to enhancement of the rate of non-radiative relaxation, which originates from the aggregation. This is beneficial for further understanding the optical characteristics of conjugated molecules.
Co-reporter:Tian-hao Huang;Ying-hui Wang;Zhi-hui Kang;Jin-bo Yao;Ran Lu
Photochemistry and Photobiology 2014 Volume 90( Issue 1) pp:29-34
Publication Date(Web):
DOI:10.1111/php.12154
Abstract
The effects of π-spacer and electron donor groups on the photophysical behaviors of fluorenone-based linear conjugated oligomers have been systemically investigated. Solvent-dependent steady-state measurements exhibit that the fluorene vinylene (FV) spacer and the electron-donating ability of donor group are able to modulate the spectral features of oligomers and the fluorescence quantum yield could decrease with the increasing of the solvent polarity. Meanwhile, quantum chemical calculation simulates their absorption spectra, and analyzes their electron transition components simultaneously. The transient absorption measurements focus on the photoexcitation dynamics of these oligomers in the toluene solution, which show that an intramolecular charge transfer state exists in the relaxation process of excited states, and its generation process could accelerate with the introduction of FV spacer and the enhancement of donor strength.
Co-reporter:Ying-Hui Wang;Lu Zou;Zhi-Hui Kang;Cheng Qian;Fuyin Wang;Yu-Guang Ma;Ran Lu;Hong Ji
Photochemistry and Photobiology 2014 Volume 90( Issue 1) pp:45-50
Publication Date(Web):
DOI:10.1111/php.12159
Abstract
We study the photophysical characters of two oligofluorenes-functionalized anthracenes molecules with different fluorine-vinylene (FV) units, which exhibits that “excimer” state appears in the solution after photoexcitation. The dynamic data shows that two mechanisms are responsible for the generation of “excimer”. The fast one is controlled by the arene-arene interaction between molecules and the slow one is influenced by the diffusion motion of molecules. Increasing the number of FV units may suppress the DM-dependent “excimer” and enhance the yield of intrinsic fluorescence, which finally improves the fluorescence property of molecules in solution.
Co-reporter:Cheng Qian;Yinghui Wang;Yunfei Song;Lu Zou;Yuguang Ma;Yanqiang Yang;Hanzhuang Zhang
Journal of Polymer Science Part B: Polymer Physics 2014 Volume 52( Issue 12) pp:842-847
Publication Date(Web):
DOI:10.1002/polb.23494
ABSTRACT
The effect of the photonic stop bands (PSBs) on the spontaneous emission from tris(8-hydroxyquinolinato)aluminum (Alq3) doped in the beads of polymethylmethacrylate opal photonic crystals (PCs) is investigated in detail. The structure of PSBs in PCs has been analyzed. The steady emission data exhibits that the first- and second-order PSB could effectively influence the spectral characteristics of Alq3 through changing the incident angles. The emission dynamic data is also investigated by using the Kohlrausch strengthened exponential model, which shows that the emission decay rate of Alq3 can be decelerated as the PSB of PC approaches the emission peak of Alq3. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 842–847
Co-reporter:Ying-Hui Wang, Jia-Qi Hou, Zhi-Hui Kang, Li-Jing Gong, Tian-Hao Huang, Li-Li Qu, Yu-Guang Ma, Ran Lu, Han-Zhuang Zhang
Chemical Physics Letters 2013 Volume 566() pp:17-20
Publication Date(Web):12 April 2013
DOI:10.1016/j.cplett.2013.02.051
We systemically investigate the photophysical properties of two star-shaped truxene based oligomers with different oligo(fluorene-vinylene) arms (Tr-OFV1 and Tr-OFV3) in solution system. The chemical quantum calculation exhibits that the electronic transition depends on the number of fluorene-vinylene (FV) groups in oligomers. The transient absorption (TA) data exhibits that increasing of FV groups in branch arms could accelerate the relaxation of excited oligomers, and the intensity-dependent exciton–exciton annihilation behavior could appear in the relaxation process of excited Tr-OFV3 and disappear in that of Tr-OFV1, indicating that their photophysical behavior is also closed to the number of FV unit.Graphical abstractHighlights► The spectral feature and transition property of Tr-OFV1 and Tr-OFV3 are studied. ► Their dynamic processes are studied by TA spectroscopy. ► Exciton annihilation is found in Tr-OFV3 solution. ► Tr-OFV3 in solution may stack due to arene–arene interaction.
Co-reporter:Tian-Hao Huang, Dan Yang, Zhi-Hui Kang, Er-Long Miao, Ran Lu, Hui-Peng Zhou, Fei Wang, Gao-Wen Wang, Peng-Fei Cheng, Ying-Hui Wang, Han-Zhuang Zhang
Optical Materials 2013 Volume 35(Issue 3) pp:467-471
Publication Date(Web):January 2013
DOI:10.1016/j.optmat.2012.09.032
Experimental and theoretical studies on the donor-dependent optical characteristics of two D–π–A–π–D type linear fluorenone-based conjugated oligomers are presented, where fluorene and triphenylamine act as the donors, respectively. Because of the strong electron-donating ability, the triphenylamine chromophores lead to red-shifts of spectral features, shorten the excited state lifetime, and enhance the two-photon fluorescence efficiency and two-photon absorption cross-section in comparison with fluorene groups. Quantum chemical calculations provide complementary information regarding the molecular structures and the frontier orbitals, which can provide a deep insight into the electronic structure and properties of oligomers.Graphical abstractHighlights► Donor-dependent optical properties of novel fluorenone-based oligomers are studied. ► Triphenylamine donor red-shifts the steady-state spectra compared to fluorene. ► Compared to fluorene donor, triphenylamine could increase the TPF efficiency. ► Triphenylamine donor could enhance the TPA cross-section compared to fluorene. ► Electronic structure and properties were learned by quantum chemical calculations.
Co-reporter:Tian-Hao Huang, Xue-Cong Li, Ying-Hui Wang, Zhi-Hui Kang, Ran Lu, Er-Long Miao, Fei Wang, Gao-Wen Wang, Han-Zhuang Zhang
Optical Materials 2013 Volume 35(Issue 7) pp:1373-1377
Publication Date(Web):May 2013
DOI:10.1016/j.optmat.2013.02.005
We compare the effects of fluorene–ethylene (FE) spacers on the photo-physical properties of fluorenone-based conjugated oligomers. The introduction of FE spacer could modulate the steady-state spectra and weaken the difference between donor-dependent spectral features. Meanwhile, the quantum chemical calculations exhibit that the electron transition mechanism modulated by FE unit is variable with the donor of oligomers. The FE π-spacer mainly rises the HOMO and facilitates the electron delocalization in the fluorene end-capped oligomer, while it lowers the LUMO and enhances the donor effect in the triphenylamine end-capped one. The time-resolved fluorescence measurement exhibits that the difference between donor-dependent excited state lifetimes of oligomers becomes less obvious after the introduction of FE units. Moreover, the nonlinear optical measurements show that the FE spacer is able to improve the two-photon fluorescence efficiency and enhance the two-photon absorption cross-section of oligomers simultaneously, but the difference in two-photon characteristics between oligomers with different donors is also decreased.Highlights► π-Spacer dependent optical properties of fluorenone-based oligomers are studied. ► Fluorene–ethylene (FE) spacer could modulate the steady-state spectra of oligomers. ► FE spacer could increase the TPF efficiency and TPA cross-section of oligomers. ► FE spacer could weaken the difference of donor-dependent optical properties. ► DFT calculations show different modulating mechanisms of FE π-spacer in oligomers.
Co-reporter:Zhi-hui Kang, Ning Sui, Ying-hui Wang, Lu Zou, Cheng Qian, Ran Lu, Han-zhuang Zhang
Journal of Molecular Structure 2013 Volumes 1054–1055() pp:89-93
Publication Date(Web):24 December 2013
DOI:10.1016/j.molstruc.2013.09.018
•Two fluorine (F) based oligomers are synthesized and investigated in detail.•F units modulate the steady-state spectra of oligomers.•DFT calculations analyze molecular structure and the electronic transition.•F units increase the TPF efficiency and the TPA cross-section of oligomers.•F units shorten the lifetime of excited oligomers.Two fluorene based linear conjugated oligomers (P-F-P and F-P-F-P-F) were synthesized where fluorene and phenothiazine groups arrange alternately. In comparison with P-F-P, two fluorene units are introduced into F-P-F-P-F, which could further enhance the π-conjugated system. Spectral measurements exhibit that the absorption and emission spectra of oligomers apparently red shift and the bandgap becomes narrow, due to the extension of π-conjugated system. The quantum chemical calculation is used to analyze their molecular structures and the electronic transition behaviors, indicating that they do not have intramolecular charge transfer character after photoexcitation. Moreover, the increasing of the two-photon absorption cross-section and the shortening of the excited state lifetime would be both attributed to the enhancement of π-conjugated system. The intensity-dependent dynamic measurement shows that no intermolecular interaction occurs in the solution, even though their π-conjugated systems are obviously enhanced.
Co-reporter:Tian-Hao Huang, Jia-Qi Hou, Zhi-Hui Kang, Ying-Hui Wang, Ran Lu, Hui-Peng Zhou, Xin Zhao, Yu-Guang Ma, Han-Zhuang Zhang
Journal of Photochemistry and Photobiology A: Chemistry 2013 Volume 261() pp:41-45
Publication Date(Web):1 June 2013
DOI:10.1016/j.jphotochem.2013.04.010
Highlights•π-Spacer dependent optical properties of fluorenone-based oligomers are studied.•Fluorene–ethylene (FE) spacer could modulate the steady-state spectra of oligomers.•DFT calculations confirm the ICT nature in the HOMO–LUMO transition.•FE spacer could increase the TPPL efficiency and TPA cross-section of oligomers.•TA measurement confirms the ICT state exists in the relaxation of excited oligomer.Effect of π-spacer on the optical properties of two novel D-π-A-π-D type fluorenone-based linear conjugated oligomers 2,7-di((E)-2-(10-octyl-10H- phenothiazin-3-yl)vinyl)-9-fluorenone (P-FO-P) and 2,7-di((E)-2-(9,9-dioctyl-7-((E)-2-(10-octyl-10H-phenothiazin-3-yl)vinyl)-9H-fluoren-2-yl)vinyl)-9-fluorenone (P-F-FO-F-P) is investigated, where fluorenone and phenothiazine units act as the electron acceptor and donor moieties, respectively. We observe that the fluorene–ethylene (FE) spacer could modulate the steady-state spectral features. Quantum chemical calculations offer complementary information regarding the frontier orbitals and molecular structures, which confirm that the intramolecular charge transfer (ICT) transition exists in the HOMO–LUMO transitions. Nonlinear optical measurements show that the FE spacer could improve the two-photon photoluminescence yield and enhance the two-photon absorption cross-section. The results of transient absorption measurements exhibit that an ICT state exists in the relaxation process of excited state, and its generation process is obviously accelerated with the introduction of π-spacer.Graphical abstract
Co-reporter:Lei Zhang;Yu Zhang;Hua Wu;Tieqiang Zhang;Pengfei Gu
Journal of Nanoparticle Research 2013 Volume 15( Issue 10) pp:
Publication Date(Web):2013 October
DOI:10.1007/s11051-013-2000-z
A theoretical model was established in this paper to analyze the properties of 3.50 and 4.39 nm PbSe quantum dot-doped liquid-core multi-mode fiber. This model was applicable to both single- and multi-mode fiber. The three-level system-based light-propagation equations and rate equations were used to calculate the guided spontaneous emission spectra. Considering the multi-mode in the fiber, the normalized intensity distribution of transversal model was improved and simplified. The detailed calculating results were thus obtained and explained using the above-mentioned model. The redshift of the peak position and the evolution of the emission power were observed and analyzed considering the influence of the fiber length, fiber diameter, doping concentration, and the pump power. The redshift increased with the increases of fiber length, fiber diameter, and doping concentration. The optimal fiber length, fiber diameter, and doping concentration were analyzed and confirmed, and the related spontaneous emission power was obtained. Besides, the normalized emission intensity increased with the increase of pump power in a nearly linear way. The calculating results fitted well to the experimental data.
Co-reporter:Ying-Hui Wang;Li-Jing Gong;Wen-Yue Dong;Ping Lu;Zhi-Hui Kang;Tian-Hao Huang;Yu-Guang Ma
Journal of Polymer Science Part B: Polymer Physics 2013 Volume 51( Issue 12) pp:992-997
Publication Date(Web):
DOI:10.1002/polb.23298
ABSTRACT
The photoexcitation processes of two donor–acceptor-type copolymers PCFBT with different ratios between the donor and the acceptor (PCFBT0.5 and PCFBT0.1) in the solution system are systematically studied. If the number of the donor is equal to that of the acceptor in one repeat unit (such as PCFBT0.5), intrachain charge transfer (ICT) can occur and participate in the relaxation of the excited state after photoexcitation. When the number of donors is much larger than that of acceptors (such as PCFBT0.1) in one repeat unit, the ICT character can disappear, and the localized exciton decay process is dominant in the relaxation of the copolymer, which also involves an excitation intensity-independent vibrational thermal relaxation process at the initial time. The results further the understanding of the basic structure-property relationship. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 992–996
Co-reporter:L. Qiao, Y. Zeng, C.Q. Qu, H.Z. Zhang, X.Y. Hu, L.J. Song, D.M. Bi, S.J. Liu
Physica E: Low-dimensional Systems and Nanostructures 2013 Volume 48() pp:7-12
Publication Date(Web):February 2013
DOI:10.1016/j.physe.2012.11.020
Using first-principles density-functional theory, the structures, stabilities, and electronic structures of the clean and oxygen atom adsorbed Zn-terminated (0001) polar surface of wurtzite ZnO have been systematically investigated. The clean polar surface exhibits n-type conductivity. The calculations of the adsorption energy indicate that the hollow (H) site at the hexagon center of the ZnO surface is the most stable site for the adsorption of oxygen atom. The adsorption of oxygen atom is an exothermic process, and the adsorption is chemisorption. After the adsorption of oxygen atom, the work function of the ZnO surface increases. This indicates that the adsorbed oxygen atom is expected to withdraw electrons from the surface and there is charge transfer from the surface to the adsorbed oxygen atom, which will cause the increase of the resistance. For the ZnO surface with adsorbed oxygen atom at the H site, the work function is the lowest. Furthermore, the modifications of the electronic structures of ZnO surface by the adsorption of oxygen atom have been investigated in terms of the electron density difference and density of states. The results indicate that there are ionic bonds formed between the surface zinc and adsorbed oxygen atoms. After the adsorption of oxygen atom, the Fermi level shifts down and the n-type conduction characteristic is significantly weakened.Graphical abstractSummary: plot of electron density difference of ZnO (0001) surface (oxygen atom adsorbed on H site). Electron depletion and accumulation are indicated in red and blue, respectively.Highlights► The clean surface exhibits n-type conductivity. ► H site of the surface is the most favorable adsorption site. ► After adsorption, work function increases, and charges transfer to the atom. ► After adsorption, Fermi level shifts down, leading to weakened n-type conductivity.
Co-reporter:Jing Wang, Li Jiang, Han Zhang, Tian-Hao Huang, Han-Zhuang Zhang
Optics Communications 2011 Volume 284(Issue 22) pp:5323-5328
Publication Date(Web):15 October 2011
DOI:10.1016/j.optcom.2011.07.053
The exact entanglement dynamics of two dipole–dipole interacting two-level atoms coupled to a common photonic band-gap (PBG) environment has been investigated. We show that the detuning conditions and the dipole–dipole interaction (DDI) are two essential ingredients and their interplay plays a crucial role in controlling the entanglement of the two-qubit system. For the negative detuning, corresponding to the case where the atomic transition frequency is inside the band gap, the entanglement of the two-qubit system can survive in the long-time limit. For the positive detuning, although the fast disentanglement presents, the DDI effects can be used to fight against the deterioration of the entanglement. The theoretical results could be applied to the implementation of quantum information processing in nanostructured materials.
Co-reporter:Wenyu Ji, Ting Wang, Bingyan Zhu, Han Zhang, Rong Wang, Dandan Zhang, Liezun Chen, Qingyi Yang and Hanzhuang Zhang
Journal of Materials Chemistry A 2017 - vol. 5(Issue 18) pp:NaN4548-4548
Publication Date(Web):2017/04/10
DOI:10.1039/C7TC00514H
Flexible quantum dot light emitting diodes (QLEDs) are highly desired due to their advantages of foldability, lightweight, and potential applications in lighting and displays. In this report, we successfully fabricated high performance red (R), green (G), and blue (B) three primary color QLEDs based on a poly(ethylene-terephthalate)/ITO/Ag/ITO (PET–IAI) cathode. The multilayer flexible IAI electrode shows outstanding stability even after bending over 2000 times with a critical bending radius of 5 mm; the sheet resistance of the IAI film only increases from 12.7 to 14.8 Ω □−1. The maximum current efficiencies are 16.3, 86.5, and 16.1 cd A−1 for RGB QLEDs, respectively, which is the best device performance for flexible RGB QLEDs reported to date. Moreover, to the best of our knowledge, these are also record efficiencies for the green and blue devices in all the reported QLEDs. Furthermore, all the devices show saturated electroluminescence (EL) with the corresponding emission peaks at 606, 530, and 478 nm for three primary color QLEDs. The superior performance is a result of high transmittance and stability of the PET–IAI film. These results signify remarkable progress in flexible QLEDs and suggest that the PET–IAI based flexible QLEDs can offer a practicable platform for foldable applications.
![Poly[2,7-(9,9-di-octyl-fluorene)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole]](/data/chemimg/133300/782469-77-6.png)
![Poly[2,7-(9,9-di-octyl-fluorene)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole]](/data/chemimg/133300/782469-77-6_b.png)