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, P_L. At low P_L, the resonance amplitude ΔI/I is ∝P_L within the PPR model, while it is ∝P²_L crossing over to P³_L 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 themore » 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:

Mkhitaryan, V. V. ^[1]; Danilovic, D. ^[1]; Hippola, C. ^[1]; Raikh, M. E. ^[2]; Shinar, J. ^[1]

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+ Show Author Affiliations

1. Ames Lab. and Iowa State Univ., Ames, IA (United States)
2. Univ. of Utah, Salt Lake City, UT (United States)

Publication Date:

Wed Jan 03 00:00:00 EST 2018

Research Org.:

Ames Lab., 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:

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