Exciton–exciton annihilation in pyrene crystals

Vol, E. D.; Goloyadov, V. A.; Kukushkin, L. S.; Naboykin, Yu. V.; Silaeva, N. B.

doi:10.1002/pssb.2220470234

Cited by 10 publications

(10 citation statements)

References 6 publications

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“…The most intense vibronic band of the dimeric ST exciton in a shallow trap or Y state appears at 535 nm for α-perylene crystals and this emission is very weak at room temperature but at temperatures <77 K, intensity increases in compensation with that of E-emission. , In the perylene crystals, the most intense component around 526 nm (19,000 cm –1 ) of the defect emission corresponds to the 0–1 band of the perylene monomer emission, while the 0–0 band appears at 500 nm (20,000 cm –1 ) and its intensity is considerably reduced by reabsorption . Thin films, nanocrystals, or nanoaggregates (thickness or sizes < 300 nm) have a large number of the monomer defect sites and hence the defect emission may be expected to be observed easily by the steady-state excitation at temperatures below 77 K or time-resolved emission spectroscopy with time resolution better than a few ns . Monomer defect emission has also been observed in the case of pyrene films or nanocrystals. , …”

Section: Results and Discussionmentioning

confidence: 99%

“…Luminescence of both free (F) and self-trapped (ST) excitons (henceforth they will be designated as dimeric excitons) have been observed in both α-pyrene and α-perylene crystals at low temperature (say, below 50 K). − In these crystals at room temperature, delocalized free excitons generated by photoexcitation are rapidly relaxed into ST excitons because of strong exciton–phonon interaction. ,− ST excitons are considered as excimers, which emit spectrally red-shifted, broadened excimer luminescence, which is a forbidden transition. − A two-step excimer formation mechanism has been proposed from the results of temperature-dependent fluorescence studies as well as ultrafast dynamics studies. ,,− However, only a few of these studies reported migration dynamics of excitons in these crystals, probably because of rapid relaxation of free excitons into excimers (within a few ps), which prevents excitons from being propagated even over a few nanometers. ,,,, In contrast to the concept that molecular excimers are trapped states and hence should be immobile, Pensack et al revealed that the excimer was diffusive and considered as a singlet exciton. ,,− However, it is now well understood that diffusivity of the dimeric excitons is much slower than that of the monomeric excitons because the resonance energy transfer process involving ST excitons must be accompanied by intermolecular structural changes that can cause the diffusion process to be thermally activated. ,,,, On the other hand, the monomeric excitons populated in the β-form of the crystals have larger mobility. ,, …”

Section: Introductionmentioning

confidence: 99%

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Exciton Dynamics in Pyrene and Perylene Nanoaggregates

Manna

Palit

2020

J. Phys. Chem. C

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Photophysical and diffusion properties of excitons generated in perylene and pyrene nanoaggregates have been investigated using steady state as well as time-resolved absorption and emission spectroscopic techniques. The average sizes and heights of the nanoaggregates prepared by the reprecipitation method have been estimated as 120 ± 20 and 60 ± 10 nm, respectively. X-ray diffraction spectra reveal that molecular packing in these nanoaggregates is very similar to that in the α-form (face-to-face pair or dimeric structure) of the crystals, but with possibilities of a large number of disordered regions consisting of monomer molecules. Therefore, following photoexcitation of nanoaggregates, both monomeric and dimeric exciton states are populated. This work, for the first time, could reveal the dynamics of interactions between these two kinds of exciton states, because of which the photophysical and diffusion properties of the excitons are significantly different from those in single crystals. Population yield of the dimeric self-trapped exciton or E state, which is the lowest energy exciton state, is negligibly small via self-trapping of dimeric excitons (dimeric channel) in the <200 ps time domain because of efficient energy transfer from dimeric excitons to monomers. However, the monomeric excitons, which are populated either independently through direct photoexcitation or by energy transfer from the dimeric excitons, contribute to an additional (monomeric) channel populating the E state via energy transfer processes occurring in the nanosecond (ns) time domain. Diffusion coefficients and diffusion lengths of the monomeric excitons estimated in both these nanoaggregates are comparable to those in the β-form of the crystals but much larger than those values reported for the α-form and hence ensure a better or comparable efficiency of energy migration in nanoaggregates as compared to that of single crystals.

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Section: Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Exciton Dynamics in Pyrene and Perylene Nanoaggregates

Manna

Palit

2020

J. Phys. Chem. C

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“…We may say that exciton diffusion in the crystal is a unique catalyst which maintains the exciton-exciton annihilation process and i s essential for observing the non-linear quenching process. Such explanation suggests that a similar effect will be observable in all crystals with small diffusion length where, a s shown in(1) , non-linear quenching i s associated with diffusion energy migration.Nevertheless it is impossible to eliminate the effect of other exciton processes which occur in case of steady-state conditions and are absent in decay kinetics of this phenomenon. In particular a further study of exciton reabsorption of exciting light quantum i s required.…”

mentioning

confidence: 73%

“…In the present note we continue our study of the exciton-exciton annihilation process in pyrene crystals which was started in (1). The temperature dependence of noii;linear luminescence quenching in pyrene crystals in the temperature range from 77 to 373 were described in detail in (1). Nonlinear quenching was studied for five fixed temperatures: T = 77, 153, 223, 293, and 373 K , for which quenching kinetics and relatiire quantum yield of steady-state luminescence versus excitation intensity were determined.…”

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confidence: 79%

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Temperature Dependence of Non‐Linear Luminescence Quenching in Pyrene Crystals

Vol

Goloyadov

Naboykin

et al. 1972

Physica Status Solidi (b)

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In the present note we continue our study of the exciton-exciton annihilation process in pyrene crystals which was started in (1). The temperature dependence of noii;linear luminescence quenching in pyrene crystals in the temperature range from 77 to 373 were described in detail in (1). Nonlinear quenching was studied for five fixed temperatures: T = 77, 153, 223, 293, and 373 K , for which quenching kinetics and relatiire quantum yield of steady-state luminescence versus excitation intensity were determined. The third harmonic of an Nd l a s e r was used for sample excitation, with exciting pulse intensity changing in large limits. 0 K i s investigated. The experimental arrangement and techniques 0The experimental results a r e shown in Fig. 1 and 2. The experimental data show a number of surprising features in the temperature dependence of non-linear quenching which will be discussed here. On the one hand the quantum yield decreases practically without changes at all temperatures studied. Using the phenomenological equation for quantum yield versus excitation intensity we estimated the blmolecular quenching coefficient and obtained p= 10 cm s almost not varying with temperature. This certainly indicates that the microscopic mechanism responsible for exciton-exciton annihilation in pyrene crystals is insensitive to temperature. A small shift with temperature observed in our output curves is accounted for by an increase in exciton intrinsic lifetime at low temperatures and.is not related to the annihilation mechanism. On the other hand it is seen from kinetic curves that a greater power i s required for detecting the decay deviation from the exponent with temperature decrease; this power acquires its critical value at liquid nitrogen temperature and leads to crystal destruction. Thus excitonexciton annihilation vanishes from decay kinetics, but it is seen in quantum yield drop as before.-14 3 -1

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Non‐Linear Fluorescence Quenching in Molecular Crystals. III. Recombination of Static Excitations

Benderskiĭ

Brikenshtein

Filippov

et al. 1981

Physica Status Solidi (b)

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Non-linear quenching of the excimer fluorescence of pyrene crystals is investigated. The transition between diffusing (T > 150 K) and static excitation (T < 70 K ) affects the relationship between the quantum yield of fluorescence @ and pumping I (from @ cc 1-112 to Q, cc 1-W at high I, respectively), and the shape of its initial decreasing portion L (from L cc t -1 to L cc t-112 for a %pulse of pumping). The rate constant of bimolecular excimer recombination y is (5 5 1.5) x x 10-11 cm3 s-l at 300 K and decreases exponentially with temperature in correspondence with the decreasing diffusion. The Forster radius R, corresponding t o the measured value of y is 30 A and agrees well with the value calculated from the spectral overlap. It is shown t h a t the low-temperature non-linear quenching is described quantitatively by the static dipoledipole excitation recombination model with approximate allowance for the three-particle correlations. Allowance for higher order correlations is found to be insignificant up to the maximum experimentally attainable excitation density n corresponding to (4n/3) R3,n x 8.Es wird die nichtlineare Tilgung der Exzimer-Fluoreszenz von Pyrenkristallen untersucht. Der ubergang zwischen diffuser (T > 150 K ) und statischer Anregung (T < 70 K) beeinfluBt, die Beziehung zwischen Quantenausbeute der Fluoreszenz @ und dem Pumpen I (von @ cc I-112 bis @ a 1 -2 1 3 bei hohem I ) und der Form des Anfangsabfalls L (von L oc t-l bis L cc t -1 1 2 fur 6-Inipulspumpen). Die bimolekulare Exzimerrekombinationsrate y ist (5 & 1,5) x 10-l' cm3 s-l bei 300 K und fallt exponentiell mit der Temperatur in ubereinstimmung mit der ?bnehmenden Diffusion. Der Forster-Radius R,, betragt, entsprechend dem MeSwert von y, 30 A und stimmt mit dem aus der spektralen nberlappung berechneten Wert iiberein. Es wird gezeigt, daS die nichtlineare Tieftemperaturtilgung quantitativ mit dem Model1 der Anregung statischer Dipole erklart werden kann, wobei naherungsweise Dreiteilchenkorrelationen beriicksichtigt werden. Es wird gefunden, daD Korrelationen hoherer Ordnung bis zu den hochsten, experimentell moglichen Anregungsdichten n unwesentlich sind, entsprechend (47~13) R:n x 8.

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Exciton–exciton annihilation in pyrene crystals

Cited by 10 publications

References 6 publications

Exciton Dynamics in Pyrene and Perylene Nanoaggregates

Exciton Dynamics in Pyrene and Perylene Nanoaggregates

Temperature Dependence of Non‐Linear Luminescence Quenching in Pyrene Crystals

Non‐Linear Fluorescence Quenching in Molecular Crystals. III. Recombination of Static Excitations

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