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Title: Comparative analysis of magnetic resonance in the polaron pair recombination and the triplet exciton-polaron quenching models

Abstract

We present a comparative theoretical study of magnetic resonance within the polaron pair recombination (PPR) and the triplet exciton-polaron quenching (TPQ) models. Both models have been invoked to interpret the photoluminescence detected magnetic resonance (PLDMR) results in π-conjugated materials and devices. We show that resonance line shapes calculated within the two models differ dramatically in several regards. First, in the PPR model, the line shape exhibits unusual behavior upon increasing the microwave power: it evolves from fully positive at weak power to fully negative at strong power. In contrast, in the TPQ model, the PLDMR is completely positive, showing a monotonic saturation. Second, the two models predict different dependencies of the resonance signal on the photoexcitation power, PL. At low PL, the resonance amplitude Δ I/I is ∝ PL within the PPR model, while it is ∝ P2L crossing over to P3L within the TPQ model. On the physical level, the differences stem from different underlying spin dynamics. Most prominently, a negative resonance within the PPR model has its origin in the microwave-induced spin-Dicke effect, leading to the resonant quenching of photoluminescence. The spin-Dicke effect results from the spin-selective recombination, leading to a highly correlated precession of the on-resonance pairmore » partners under the strong microwave power. This effect is not relevant for TPQ mechanism, where the strong zero-field splitting renders the majority of triplets off resonance. On the technical level, the analytical evaluation of the line shapes for the two models is enabled by the fact that these shapes can be expressed via the eigenvalues of a complex Hamiltonian. This bypasses the necessity of solving the much larger complex linear system of the stochastic Liouville equations. Lastly, our findings pave the way towards a reliable discrimination between the two mechanisms via cw PLDMR.« less

Authors:
 [1];  [1];  [1];  [2];  [1]
  1. Ames Lab. and Iowa State Univ., Ames, IA (United States)
  2. Univ. of Utah, Salt Lake City, UT (United States)
Publication Date:
Research Org.:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1417356
Alternate Identifier(s):
OSTI ID: 1415524
Report Number(s):
IS-J-9557
Journal ID: ISSN 2469-9950; PRBMDO; TRN: US1801042
Grant/Contract Number:  
AC02-07CH11358; FG02-06ER46313
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 97; Journal Issue: 3; Journal ID: ISSN 2469-9950
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Mkhitaryan, V. V., Danilovic, D., Hippola, C., Raikh, M. E., and Shinar, J. Comparative analysis of magnetic resonance in the polaron pair recombination and the triplet exciton-polaron quenching models. United States: N. p., 2018. Web. doi:10.1103/PhysRevB.97.035402.
Mkhitaryan, V. V., Danilovic, D., Hippola, C., Raikh, M. E., & Shinar, J. Comparative analysis of magnetic resonance in the polaron pair recombination and the triplet exciton-polaron quenching models. United States. doi:10.1103/PhysRevB.97.035402.
Mkhitaryan, V. V., Danilovic, D., Hippola, C., Raikh, M. E., and Shinar, J. Wed . "Comparative analysis of magnetic resonance in the polaron pair recombination and the triplet exciton-polaron quenching models". United States. doi:10.1103/PhysRevB.97.035402. https://www.osti.gov/servlets/purl/1417356.
@article{osti_1417356,
title = {Comparative analysis of magnetic resonance in the polaron pair recombination and the triplet exciton-polaron quenching models},
author = {Mkhitaryan, V. V. and Danilovic, D. and Hippola, C. and Raikh, M. E. and Shinar, J.},
abstractNote = {We present a comparative theoretical study of magnetic resonance within the polaron pair recombination (PPR) and the triplet exciton-polaron quenching (TPQ) models. Both models have been invoked to interpret the photoluminescence detected magnetic resonance (PLDMR) results in π-conjugated materials and devices. We show that resonance line shapes calculated within the two models differ dramatically in several regards. First, in the PPR model, the line shape exhibits unusual behavior upon increasing the microwave power: it evolves from fully positive at weak power to fully negative at strong power. In contrast, in the TPQ model, the PLDMR is completely positive, showing a monotonic saturation. Second, the two models predict different dependencies of the resonance signal on the photoexcitation power, PL. At low PL, the resonance amplitude ΔI/I is ∝PL within the PPR model, while it is ∝P2L crossing over to P3L within the TPQ model. On the physical level, the differences stem from different underlying spin dynamics. Most prominently, a negative resonance within the PPR model has its origin in the microwave-induced spin-Dicke effect, leading to the resonant quenching of photoluminescence. The spin-Dicke effect results from the spin-selective recombination, leading to a highly correlated precession of the on-resonance pair partners under the strong microwave power. This effect is not relevant for TPQ mechanism, where the strong zero-field splitting renders the majority of triplets off resonance. On the technical level, the analytical evaluation of the line shapes for the two models is enabled by the fact that these shapes can be expressed via the eigenvalues of a complex Hamiltonian. This bypasses the necessity of solving the much larger complex linear system of the stochastic Liouville equations. Lastly, our findings pave the way towards a reliable discrimination between the two mechanisms via cw PLDMR.},
doi = {10.1103/PhysRevB.97.035402},
journal = {Physical Review B},
issn = {2469-9950},
number = 3,
volume = 97,
place = {United States},
year = {2018},
month = {1}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Figures / Tables:

FIG. 1: FIG. 1:: Schematics of the processes underlying the PPR model. The black arrows indicate the PP generation; out of g PPs per second, g/4 are singlets and 3g/4 – triplets. The brown and green arrows respectively indicate the dissociation and recombination, Eq. (9). The orange arrows represent the singlet-triplet beating,more » induced by the hyperfine coupling and resonance microwave, Eq. (8), and the spin-lattice relaxation, Eq. (10). The yellow background outlines the components of the stochastic Liouville Equation (7).« less

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    Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.