Exciton lifetimes

PM spectra and their decays in DOO-PPV films and dilute solutions, we conclude that the primary excitations in DOO-PPV films are also singlet excitons [26]. The long excitonic lifetime and a corresponding high PL quantum efficiency [27] indicates that DOO-PPV is a high quality polymer material, which is very suitable for electrooptics and laser action applications [28],... 

Since GaN materials contain a high density of extended defects (10 - 1010 cm 2), it is expected that the carrier and exciton recombination dynamics vary from sample to sample. Studies have revealed that the exciton lifetime is correlated with the yellow emission line at about 2.2 eV the stronger the yellow... 

If an exciton hops about, starting from some initial site and ends up at another site at the time of its disappearance for one reason or another, the linear distance between these sites is called the diffusion length, lA. The diffusion length is related to the diffusion coefficient D through the exciton lifetime t ... 

Case II The triplet exciton lifetime is dominated by the T2 term in this regime, and... 

In these equations, n is the exciton concentration, t is time, a is the absorption coeflScient for the incident light, Z is the intensity of the incident light, K is the two-photon absorption rate constant at 532 nm, (3 is the reciprocal of the exciton lifetime, and y is the exciton-exciton annihilation rate constant. 

The absorption coeflScient a was determined to be 2.4 X 10 cm at 320 nm and 9.2 X 10 cm at 280 nm by measuring the optical density and thickness of several films. The exciton lifetime t t — 1/p) was measured by using frequency-doubled light from a 200-ps neodymium-doped YAG laser... 

For both experiments, we assumed that dnidt = 0, because the exciton lifetime is considerably shorter than the excitation light pulse width. Therefore, for the two-photon experiment at light intensities such that (3n, K = We found k = 10 cm /s at 532 nm. The solid curve in... 

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