Optically detected electron paramagnetic resonance of arsenic antisites in low‐temperature GaAs layers

1992 ◽  
Vol 60 (6) ◽  
pp. 718-720 ◽  
Author(s):  
H.‐J. Sun ◽  
G. D. Watkins ◽  
F. C. Rong ◽  
L. Fotiadis ◽  
E. H. Poindexter
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Low Temperature ◽  
Paramagnetic Resonance ◽  
Optically Detected ◽  
Low Temperature Gaas ◽  
Electron Paramagnetic

Electrically and Optically Detected Electron Paramagnetic Resonance in Blue Organic Light Emitting Diodes

2021 ◽  
Author(s):  
◽  
Rebecca Jane Sutton
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Light Emitting Diodes ◽  
Organic Light Emitting Diodes ◽  
Great Promise ◽  
Paramagnetic Resonance ◽  
Light Emitting ◽  
Emissive Layer ◽  
Organic Light ◽  
Optically Detected ◽  
Electron Paramagnetic

<p>Organic light emitting diodes (OLEDs) are an emerging technology based on electrically conducting polymer films, with great promise for large area lighting and flexible ultra-thin displays. However, despite the rapid technological development, there is still a poor understanding of the degradation and spindependent recombination processes that take place inside an OLED. In this thesis, Electron Paramagnetic Resonance (EPR) was used to investigate these processes in blue-emitting OLEDs.  A successful procedure was developed and refined for fabricating OLEDs with the structure ITO/PEDOT:PSS/emissive layer/Al/Ag, with and without the PEDOT:PSS hole-transporting layer. The organic emissive layer was either F8BT, PFO, or PVK:OXD-7:FIrpic (PB). These OLEDs were fabricated in air and with a geometry optimised for EPR experiments. Critical features for satisfactory devices were found to be a sufficiently thick organic layer and minimal exposure to the air.  A compact apparatus was developed for simultaneous light output, current, and voltage measurements on the OLEDs while in an inert glove box environment. Electroluminescence and current-voltage parameters measured for these devices showed predominantly trap-controlled space-charge-limited conduction.   OLEDs with PFO as the emissive layer and with a PEDOT:PSS layer were investigated with conventional, electrically-detected (ED) and optically-detected (OD) EPR techniques. EDEPR and ODEPR signals were observed at ~9.2 GHz and in the low (<50 mT) and high (~330 mT) magnetic field regimes and were found to change markedly with time during operation as the device degraded. The low field signals initially showed a composite broad quenching and superimposed narrow enhancing response centred around zero field strength. These signals were attributed to magneto-resistance (MR) and magneto-electroluminescence (MEL). Following operational ageing, a third, narrow quenching line was observed in the MR and the ratio of the initial two MR responses changed substantially. These effects are tentatively attributed to a hyperfine interaction.  For both EDEPR and ODEPR, quenching high field resonances with a g-value (gyromagnetic ratio) of 2.003±0.001 were observed. The current-quenching resonance gradually diminished during operation and after 4–5 hours was replaced by a current-enhancing resonance. The appearance of this latter resonance could be explained by chemical changes in the OLED due to the diffusion of oxygen through the device from the oxygen-plasma-treated ITO. A working model is proposed which can explain this observed change as spindependent trapping and recombination at free radicals, although the model requires further experimentation to test its validity.</p>

Electron Paramagnetic Resonance in Spinach Chloroplasts at Low Temperature

Nature ◽  
1964 ◽  
Vol 204 (4963) ◽  
pp. 1076-1078 ◽  
Author(s):  
POWER SOGO ◽  
RUSSELL FAUCETT ◽  
THOMAS HOLZER
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Low Temperature ◽  
Paramagnetic Resonance ◽  
Spinach Chloroplasts ◽  
Electron Paramagnetic

Free radical metabolites in myocardium during ischemia and reperfusion

1991 ◽  
Vol 261 (4) ◽  
pp. L81-L86 ◽  
Author(s):  
Enno K. Ruuge ◽  
Alexander N. Ledenev ◽  
Vladimir L. Lakomkin ◽  
Alexander A. Konstantinov ◽  
Marina Yu. Ksenzenko
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Free Radical ◽  
Low Temperature ◽  
Coenzyme Q ◽  
Heart Tissue ◽  
Paramagnetic Species ◽  
Spectral Parameters ◽  
Paramagnetic Resonance ◽  
Oxygen Paradox ◽  
Electron Paramagnetic

Low-temperature electron paramagnetic resonance (EPR) spectroscopy and spin traps were used to measure paramagnetic species generation in rat hearts and isolated mitochondria. The hearts were freeze-clamped at 77 K during control perfusion by the Langendorff procedure, after 20–30 min of normothermic ischemia or 10–30 s of reperfusion with oxygenated perfusate. All EPR spectra measured at 4.5–50 K exhibited signals of both mitochondrial free radical centers and FeS proteins. The analysis of spectral parameters measured at 243 K showed that free radicals in heart tissue were semiquinones of coenzyme Q10 and flavins. The appearance of a typical “doublet” signal at g = 1.99 in low-temperature spectra indicated that a part of ubisemiquinones formed a complex with a high potential FeS protein of succinate dehydrogenase. Ischemia decreased the free radical species in myocardium ≈50%; the initiation of reflow of perfusate resulted in quick increase of the EPR signal. Mitochondria isolated from hearts during control perfusion and after 20–30 min of ischemia were able to produce superoxide radicals in both the NADH-coenzyme Q10 reductase and the bc1 segments of the respiratory chain. The rate of oxyradical generation was significantly higher in mitochondria isolated from ischemic heart. electron paramagnetic resonance; oxygen paradox; oxyradicals; rat heart; semiquinones

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