Aggregate Formation in Pyridine-Based Polymers

1995 ◽  
Vol 413 ◽  
Author(s):  
J. W. Blatchford ◽  
S. W. Jessen ◽  
L. B. Lin ◽  
T. L. Gustafson ◽  
A. J. Epsteint ◽  
...  
Keyword(s):  
Thick Film ◽  
Stokes Shift ◽  
Spectroscopic Properties ◽  
Phenylene Vinylene ◽  
Aggregate Formation ◽  
Photoinduced Absorption ◽  
Time Resolved ◽  
Vibronic Structure ◽  
Time Resolved Photoluminescence ◽  
Versus Solution

ABSTRACTThe spectroscopic properties of the pyridine-based polymer poly(p-pyridyl vinylene p-phenylene vinylene) (PPyVPV) are examined. The emission of PPyVPV in solution has small intrinsic Stokes shift with some vibronic structure. In contrast, emission from thick film samples is featureless, with a strong redshift of ˜0.5 eV versus solution. We attribute these observations to the formation of aggregate states in film samples. Time-resolved photoluminescence measurements are in accord with the diffusion of excitons to the aggregate sites. Photoinduced absorption also originates from excitons in aggregate states.

scholarly journals Towards hydrophobic carminic acid derivatives and their incorporation in polyacrylates

2018 ◽  
Vol 5 (7) ◽  
pp. 172399 ◽  
Author(s):  
Luca Gabrielli ◽  
Davide Origgi ◽  
Giuseppe Zampella ◽  
Luca Bertini ◽  
Simone Bonetti ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Dimethyl Sulfoxide ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Spectroscopic Properties ◽  
Carminic Acid ◽  
Functional Theory ◽  
Time Resolved ◽  
Sugar Ring ◽  
Time Resolved Photoluminescence

Carminic acid, a natural hydrophilic dye extensively used in the food and cosmetic industries, is converted in hydrophobic dyes by acetylation or pivaloylation. These derivatives are successfully used as biocolourants for rubber objects. In this paper, spectroscopic properties of the carminic acid derivatives in dimethyl sulfoxide and in polybutylacrylate are studied by means of photoluminescence and time-resolved photoluminescence decays, revealing a hypsochromic effect due to the presence of bulky substituents as the acetyl or pivaloyl groups. Molecular mechanics and density functional theory calculations confirm the disruption of planarity between the sugar ring and the anthraquinoid system determined by the esterification.

Recombination Dynamics in Nitride Quantum Boxes and Quantum Wells for Colors Ranging from the UV to the Red

2000 ◽  
Vol 639 ◽  
Author(s):  
P. Lefebvre ◽  
A. Morel ◽  
M. Gallart ◽  
T. Taliercio ◽  
B. Gil ◽  
...  
Keyword(s):  
Quantum Well ◽  
Quantum Wells ◽  
Electric Fields ◽  
Room Temperature ◽  
Stokes Shift ◽  
Oscillator Strengths ◽  
Time Resolved ◽  
Transition Energies ◽  
Radiative Efficiency ◽  
Time Resolved Photoluminescence

ABSTRACTTime-resolved photoluminescence experiments at varying temperature are performed on a series of InxGa1−xN/GaN quantum well and quantum box samples of similar compositions (0.15 < x < 0.20). The results are analyzed by using envelope-function calculations of transition energies and oscillator strengths, accounting for internal electric fields. The respective influences of localization and electric fields on radiative and nonradiative lifetimes and on the Stokes shift are deduced. The results indicate that the spatial extension of localization centers is much smaller than the size of the quantum boxes (∼10 × 3 nm, typically). The room-temperature radiative efficiency of both quantum well and quantum box samples is enhanced by replacing the topmost GaN barrier by an AlGaN one.

Photoexcitation Dynamics In Polymeric Heterostructures

1995 ◽  
Vol 413 ◽  
Author(s):  
G. Bongiovanni ◽  
S. Destri ◽  
A. Mura ◽  
A. Piaggi ◽  
R Tubino
Keyword(s):  
Density Of States ◽  
Exponential Decay ◽  
Stokes Shift ◽  
Photoluminescence Intensity ◽  
Nearest Neighbour ◽  
Time Resolved ◽  
Thermally Activated ◽  
Spectral Relaxation ◽  
Site Selective ◽  
Time Resolved Photoluminescence

ABSTRACTWe investigate the dynamics of photoexcitations in thiophene-based copolymers by site-selective and time-resolved photoluminescence spectroscopies. We attribute the large Stokes-shift observed between the absorption and luminescence peaks to spectral relaxation of excitons within an inhomogeneously broadened density of states. The non exponential decay of the photoluminescence intensity is explained through the interplay between spectral diffusion, thermally activated jumps and slow transfer to non nearest neighbour sites.

Exciton dynamics in thick GaN MOVPE epilayers deposited on sapphire.

1997 ◽  
Vol 2 ◽  
Author(s):  
J. Allègre ◽  
P. Lefebvre ◽  
J. Camassel ◽  
B. Beaumont ◽  
Pierre Gibart
Keyword(s):  
Layer Thickness ◽  
Buffer Layers ◽  
Rate Equations ◽  
Time Resolved ◽  
Versus Layer ◽  
Level Model ◽  
Shallow Impurities ◽  
Aln Buffer ◽  
Time Resolved Photoluminescence

Time-resolved photoluminescence spectra have been recorded on three GaN epitaxial layers of thickness 2.5 μm, 7 μm and 16 μm, at various temperatures ranging from 8K to 300K. The layers were deposited by MOVPE on (0001) sapphire substrates with standard AlN buffer layers. To achieve good homogeneities, the growth was in-situ monitored by laser reflectometry. All GaN layers showed sharp excitonic peaks in cw PL and three excitonic contributions were seen by reflectivity. The recombination dynamics of excitons depends strongly upon the layer thickness. For the thinnest layer, exponential decays with τ ~ 35 ps have been measured for both XA and XB free excitons. For the thickest layer, the decay becomes biexponential with τ1 ~ 80 ps and τ2 ~ 250 ps. These values are preserved up to room temperature. By solving coupled rate equations in a four-level model, this evolution is interpreted in terms of the reduction of density of both shallow impurities and deep traps, versus layer thickness, roughly following a L−1 law.

ZnCdO/ZnMgO and ZnO/AlGaN Heterostructures for UV and Visible Light Emitters

2005 ◽  
Vol 892 ◽  
Author(s):  
Andrei Osinsky ◽  
Jianwei Dong ◽  
J. Q. Xie ◽  
B. Hertog ◽  
A. M. Dabiran ◽  
...  
Keyword(s):  
Molecular Beam ◽  
Compositional Analysis ◽  
Optical Emission ◽  
Rf Plasma ◽  
Light Emitters ◽  
Time Resolved ◽  
Light Emitting ◽  
Spatially Resolved ◽  
Time Resolved Photoluminescence ◽  
Made In

AbstractThis paper reviews of some of the progress made in the development of ZnO-based light emitting diodes (LEDs). n-ZnO/p-AlGaN-based heterostructures have been successfully for the fabrication of UV emitting LEDs that have operated at temperatures up to 650K, suggesting an excitonic origin for the optical transitions. RF-plasma-assisted molecular beam epitaxy has been used to grow epitaxial CdxZn1-xO films on GaN/sapphire structure. These films have a single-crystal wurtzite structure as demonstrated by structural and compositional analysis. High quality CdxZn1-xO films were grown with up to x=0.78 mole fraction as determined by RBS and SIMS techniques. Optical emission ranging from purple (Cd0.05Zn0.95O) to yellow (Cd0.29Zn0.71O) was observed. Compositional fluctuations in a Cd0.16Zn0.84O films were not detected by spatially resolved CL measurements, although intensity fluctuation with features of ∼0.5 μm diameter were seen on the intensity maps. Time resolved photoluminescence shows multi-exponential decay with 21 psec. and 49±3 psec. lifetimes, suggesting that composition micro-fluctuations may be present in Cd0.16Zn0.84O film.

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