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Optically Detected Magnetic Resonance (ODMR) and its Application to p -Conjugated Materials and Organic Light-Emitting Devices (OLEDs) Joseph Shinar March 30, 2009 email@example.com.
and its Application to
p-Conjugated Materials and
Organic Light-Emitting Devices (OLEDs)
March 30, 2009
ODMR in One Sentence:Monitor mwave-induced changes in an optical quantity at the field for resonance.Since “optical quantity” can mean different quantities, ODMR is an umbrella term, meaning we can measure, e.g.,* Photoluminescence (PL)-detected magnetic resonance (PLDMR)* Electroluminescence (EL)-detected magnetic resonance (ELDMR)* Absorption-detected magnetic resonance (ADMR)* Photoinduced absorption (PA)-detected magnetic resonance (PADMR)
Similarly, Electrically Detected Magnetic Resonance (EDMR) in One Sentence:Monitor mwave-induced changes in an electrical quantity at the field for resonance.And similarly,, EDMR is an umbrella term, e.g.,* Current or Conductivity-detected magnetic resonance (CDMR)* Photoconductivity-detected magnetic resonance (PCDMR)
TRIPLET SINGLET POLARON
(EXCITON) (EXCITON) MANIFOLD
absorptionknrkr (PL 0-0 )
The positive PLDMR in poly(3-hexyl thiophene) (P3HT) and poly(3-dodecyl thiophene) (P3DT) films and solutions.
L. S. Swanson et al., Phys. Rev. Lett. 65, 1140 (1990).
DIPL/IPL = 1.4 x 10-3
DIPL/IPL = 3.3 x 10-4
DIPL/IPL = 8 x 10-5
E. J. W. List et al., Appl. Phys. Lett. 76, 2083 (2000).
PADMR of m-LPPP films [scan probe energy at constant magnetic field; monitor microwave induced changes in the photoinduced absorption (PA)].
Single modulation PLDMR DPL/PL vs the microwave modulation frequency fM.
The dashed line is a single lifetime fit w/
t = 38 ms;
the solid line is a two-lifetime fit w/
t1= 24 ms, t2= 244 ms.
Note: negative carrier electron (e-) negative polaron (p-) radical anionpositive carrier hole (h+) positive polaron (p-) radical cation
1. Double modulation (DM) PLDMR (DM-PLDMR)
2. Joint thermally-stimulated luminescence (TSL) + PLDMR
3. PLDMR of the small molecules
tris(8-hydroxy quinoline) Al (Alq3) &
Double Modulation PLDMR (DM-PLDMR)[M. K. Lee et al., Phys. Rev. Lett. 94, 137403 (2005)M. Segal et al., Phys. Rev. B 71, 245201(2005)]
the PL that is faster than nLaser [PL(nLaserPR)]
referenced by the microwaves, which are modulated at nmw.
That output is connected to Lockin #1, synchronized to fM = 200 Hz.
As fL increases to 100 kHz, the spin 1/2 PLDMR due to delayed PL of polaron pairs with t 10 ms should decrease to zero. In contrast, the PLDMR due to quenching should remain essentially unchanged.
DM-PLDMR vs wL = 2pfL,
which is a measurement in the frequency domain,
is equivalent to
time-resolved PLDMR vs t,
which is a measurement in the time domain.
Dashed line: Behavior predicted by the delayed PL model.
Behavior predicted by the quenching model is flat, as observed.
low temperature, detrapped by warming up, find each other, &
recombine. Some of those which recombine to SEs yield the TSL.
the very mechanism invoked by Wohlgenannt & Vardeny
as the origin of the positive spin ½ PLDMR & negative spin ½ PADMR.
Note the growth of the quenching resonance @
lower microwave chopping frequencies.
Behavior similar to positive spin 1/2 PLDMR in polymers – cannot be due to delayed PL mechanism.
G. Li et al., Phys. Rev. B 69, 165311 (2004).
G. Li et al., Phys. Rev. B 69, 165311(2004); Phys. Rev. B 71, 235211 (2005).
ODMR is a powerful tool to study the dynamics of polarons, bipolarons, trions, TEs, and SEs in p-conjugated materials & OLEDs.