Combined theoretical and time-resolved photoluminescence investigations of [Mo6Bri8Bra6]2− metal cluster units: evidence of dual emission

2015 ◽  
Vol 17 (43) ◽  
pp. 28574-28585 ◽  
Author(s):  
K. Costuas ◽  
A. Garreau ◽  
A. Bulou ◽  
B. Fontaine ◽  
J. Cuny ◽  
...  
Keyword(s):  
Excited States ◽  
Metal Cluster ◽  
Energy Shift ◽  
Dual Emission ◽  
Time Resolved ◽  
Nir Emission ◽  
Triplet Excited States ◽  
Time Resolved Photoluminescence

Distinct emissive species have been identified in [Mo6Bri8Bra6]2− containing systems. Strong geometrical relaxations of the triplet excited states are responsible for the huge energy shift leading to intense red-NIR emission.

scholarly journals Two - Color Mid-Infrared Spectroscopy of Isoelectronic Centers in Silicon

2003 ◽  
Vol 770 ◽  
Author(s):  
N.Q. Vinh ◽  
T. Gregorkiewicz
Keyword(s):  
Excited States ◽  
Free Electron ◽  
Free Electron Laser ◽  
Materials Science ◽  
Time Resolved ◽  
Mid Infrared ◽  
Semiconductor Physics ◽  
Open Questions ◽  
Time Resolved Photoluminescence ◽  
Tunable Source

AbstractOne of the open questions in semiconductor physics is the origin of the small splittings of the excited states of bound excitons in silicon. A free electron laser as a tunable source of the mid-infrared radiation (MIR) can be used to investigate such splittings of the excited states of optical centers created by transition metal dopants in silicon. In the current study, the photoluminescence from silver and copper doped silicon is investigated by two color spectroscopy in the visible and the MIR. It is shown the PL due recombination of exciton bound to Ag and Cu is quenched upon application of the MIR beam. The time-resolved photoluminescence measurements and the quenching effects of these bands are presented. By scanning the wavelength of the free-electron laser ionization spectra of relevant traps involved in photoluminescence are obtained. The formation and dissociation of the bound excitons, and the small splittings of the effective-mass excited states are discussed. The applied experimental method allows correlation of DLTS data on trapping centers to specific channels of radiative recombination. It can be applied for spectroscopic analysis in materials science of semicondutors.

State filling and time-resolved photoluminescence of excited states inInxGa1−xAs/GaAs self-assembled quantum dots

1996 ◽  
Vol 54 (16) ◽  
pp. 11548-11554 ◽  
Author(s):  
S. Raymond ◽  
S. Fafard ◽  
P. J. Poole ◽  
A. Wojs ◽  
P. Hawrylak ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Excited States ◽  
Time Resolved ◽  
Self Assembled ◽  
Time Resolved Photoluminescence ◽  
State Filling

Bond Shortening (1.4 Å) in the Singlet and Triplet Excited States of [Ir2(dimen)4]2+in Solution Determined by Time-Resolved X-ray Scattering

2011 ◽  
Vol 50 (19) ◽  
pp. 9329-9336 ◽  
Author(s):  
Kristoffer Haldrup ◽  
Tobias Harlang ◽  
Morten Christensen ◽  
Asmus Dohn ◽  
Tim Brandt van Driel ◽  
...  
Keyword(s):  
Excited States ◽  
Time Resolved ◽  
X Ray ◽  
X Ray Scattering ◽  
Triplet Excited States ◽  
Ray Scattering

scholarly journals Spectroscopic investigation of excitonic and charge photogeneration processes in organic photovoltaic cells

2021 ◽  
Author(s):  
◽  
Joseph Gallaher
Keyword(s):  
Excited States ◽  
Charge Separation ◽  
Transient Absorption ◽  
Mirror Image ◽  
Triplet Exciton ◽  
Organic Photovoltaic ◽  
Charge Generation ◽  
Time Resolved ◽  
Blend Morphology ◽  
Time Resolved Photoluminescence

<p>Organic photovoltaic (OPV) cells show significant promise as a renewable energy resource capable of meeting the world’s large and growing energy needs. Increasing device efficiency is central to achieving an economically viable option for widespread applications. To this end, a better understanding of the structure and dynamics of the electronic excited states is needed. In particular, the mechanism by which excitons (electron-hole pairs) escape their Coulombic attraction and generate photocurrent is yet to be established. In this thesis ultrafast laser spectroscopy, in particular transient absorption and time-resolved photoluminescence, are used to study: exciton relaxation, morphological effects on charge separation, and the pathway leading to triplet exciton states.  In Chapter 3, a series of oligothiophenes are synthesised with well-defined conjugation lengths to act as molecular models of polymer backbone sub-units, and thereby probe exciton relaxation processes. Time-resolved photoluminescence (TRPL) and transient absorption (TA) spectroscopy measurements presented in Chapter 4 reveal emission signatures evolve from a mirror image of absorption - which lacks vibronic structure - towards a spectrally narrower and vibronically structured species on the hundreds of femtosecond to early picosecond timescale. Analysis of this spectral evolution shows that a broad distribution of torsional conformers is driven to rapidly planarize in the excited state, including in solid films. This provides evidence that both torsional relaxation and energy migration could contribute to the non-mirror image absorption-emission spectra observed in polymer thin films.  Recently, long lived TA signatures have been attributed to triplet excited states with the suggested formation pathway being similar to organic light emitting diodes, whereby non-geminate (bimolecular) charge recombination leads to the formation of both singlet and triplet states. Isolated oligothiophenes in solution provide an ideal model system to investigate the role of structural relaxation on triplet exciton formation. Through analysis of TA spectral dynamics in Chapter 5, singlet and triplet exciton populations were tracked. Restriction of the torsional relaxation increased triplet yield suggesting vibrational hot states could drive triplet formation. This model could aid in understanding triplet exciton formation in polymer-based solar cells via spin-mixing instead of non-geminate recombination.  In a series of polymer:fullerene blends, the link between the nature of polymerfullerene intermixing and charge generation pathways was investigated. It is shown in Chapter 6 that free charge generation is most efficient in a 3-phase morphology that features intimately mixed polymer:fullerene regions amongst neat polymer and fullerene phases. Distinct spectroscopic signatures made it possible to determine whether holes occupy disordered or crystalline polymer chains. TA spectral dynamics reveal the migration of holes from intermixed to pure olymer regions in 3-phase morphology blends, which contrasted with observations in 2-phase blends. The energy gradient between the intermixed and phase-pure regions may be sufficient to drive efficient separation of charge pairs initially generated in intermixed regions, with free charges subsequently percolating through these phase-pure domains.  The photophysics of a high performance polymer:polymer blend is studied in Chapter 7 in an effort to elucidate how these blends can rival their polymer:fullerene counterparts. Optical spectroscopy reveals incomplete exciton dissociation and rapid geminate recombination in the blends. This is shown to result from a largely phase-separated morphology with domains greater than the exciton diffusion length. Significant loss of charge carriers on early timescales highlights increasing polymer: polymer solar cell efficiency requires optimizing blend morphology to realise facile charge separation.  Taken together, this thesis presents a valuable spectroscopic insight into the pathway of efficient charge separation and the importance of both blend morphology and polymer structure.</p>

scholarly journals Manipulating spatial alignment of donor and acceptor in host-guest MOF for TADF

2021 ◽  
Author(s):  
Xiao-Ting Liu ◽  
Weijie Hua ◽  
Hong-Xiang Nie ◽  
Mingxing Chen ◽  
Ze Chang ◽  
...  
Keyword(s):  
Excited States ◽  
Delayed Fluorescence ◽  
Energy Splitting ◽  
Time Resolved ◽  
Face To Face ◽  
Spatial Alignment ◽  
Stacking Pattern ◽  
Donor And Acceptor ◽  
Loading Ratio ◽  
Triplet Excited States

Abstract Thermally activated delayed fluorescence (TADF) was achieved when electron-rich triphenylene (Tpl) donors (D) were confined to a cage-based porous MOF host (NKU-111) composed of electron-deficient 2,4,6-tri(pyridin-4-yl)-1,3,5-triazine (Tpt) acceptor (A) as the ligand. The spatially-separated D and A molecules in a face-to-face stacking pattern generated strong through-space charge transfer (CT) interactions with a small singlet-triplet excited states energy splitting (∼0.1 eV), which enabled TADF. The resulting Tpl@NKU-111 exhibited an uncommon enhanced emission intensity as the temperature increased. Extensive steady-state and time-resolved spectroscopic measurements and first-principles simulations revealed the chemical and electronic structure of this compound in both the ground and low-lying excited states. A double-channel (T1, T2) intersystem crossing mechanism with S1 was found and explained as single-directional CT from the degenerate HOMO-1/HOMO of the guest donor to the LUMO + 1 of one of the nearest acceptors. The rigid skeleton of the compound and effective through-space CT enhanced the photoluminescence quantum yield (PLQY). A maximum PLQY of 57.36% was achieved by optimizing the Tpl loading ratio in the host framework. These results indicate the potential of the MOFs for the targeted construction and optimization of TADF materials.

Switching on Near-Infrared Light in Lanthanide-doped CsPbCl3 Perovskite Nanocrystals.pdf

2020 ◽  
Author(s):  
Min Zeng ◽  
Federico Locardi ◽  
Dimitrije Mara ◽  
Zeger Hens ◽  
Rik Van Deun ◽  
...  
Keyword(s):  
Energy Transfer ◽  
Near Infrared ◽  
Lanthanide Ions ◽  
Infrared Light ◽  
Quantum Yields ◽  
General Strategy ◽  
Time Resolved ◽  
Nir Emission ◽  
Photoluminescence Studies ◽  
Time Resolved Photoluminescence

The accessible emission spectral range of lead halide perovskite (LHP) CsPbX3 (X = Cl−, Br−, I−) nanocrystals (NCs) has remained so far limited to wavelengths below 1 μm, corresponding to the emission line of Yb3+, whereas the direct sensitization of other near-infrared (NIR) emitting lanthanide ions is unviable. Herein, we present a general strategy to enable intense NIR emission from Er3+ at ~1.5 μm, Ho3+ at ~1.0 μm and Nd3+ at ~1.06 μm through a Mn2+-mediated energy-transfer pathway. Steady-state and time-resolved photoluminescence studies show that energy-transfer efficiencies of about 39%, 35% and 70% from Mn2+ to Er3+, Ho3+ and Nd3+ are obtained, leading to photoluminescence quantum yields of ~0.8%, ~0.7% and ~3%, respectively. This work provides guidance on constructing energy-transfer pathways in semiconductors and opens new perspectives for the development of lanthanide-functionalized LHPs as promising materials for optoelectronic devices operating in the NIR region.

Optimization of a Safranine O three-component photoinitiating system for use in holographic recording

2015 ◽  
Vol 93 (12) ◽  
pp. 1345-1353 ◽  
Author(s):  
Ahmad Ibrahim ◽  
Bandar El Fouhaili ◽  
Aurélie Chan Yong ◽  
Christian Ley ◽  
Xavier Allonas ◽  
...  
Keyword(s):  
Excited States ◽  
Irradiation Time ◽  
Holographic Recording ◽  
Time Resolved ◽  
The Matrix ◽  
Resin Formulation ◽  
High Diffraction Efficiency ◽  
Triplet Excited States ◽  
Safranine O ◽  
High Diffraction

The coupling between a holographic resin, combining multiple monomers and additives, with photoinitiating systems (PIS) is not straightforward. In this paper, a classic PIS based on Safranine O (SFH+) as dye, an amine (ethyl-4-(dimethylamino)benzoate) as electron donor, and a triazine derivative (2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine) as electron acceptor for holographic recording was studied using time-resolved spectroscopic experiments. By taking into account the viscosity of the matrix, a method to evaluate the overall quantum yield of radicals released is proposed and the contribution of singlet and triplet excited states of SFH+ in the formation of radicals is evaluated. Then the corresponding photopolymerization efficiencies of the PIS, studied by real-time FTIR, are compared with holographic recording experiments: this system allows the formation of a hologram with high diffraction efficiency (0.9) in 3 s of irradiation time. It is shown that besides holographic resin formulation, the photochemistry of PIS also impacts the hologram formation.

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