Luminescence quantum efficiency

A critical parameter in determining the operating efficiency of polymer LEDs is the luminescence quantum efficiency of singlet excilons in the polymer i.e. the probability that a singlet exciton will decay radiatively. The luminescence quantum elft-... 

Also, using dyes as laser media or passive mode-locked compounds requires numerous special parameters, the most important of which arc file band position and bandwidth of absorption and fluorescence, the luminescence quantum efficiency, the Stokes shift the possibility of photoisomcrization, chemical stability, and photostability. Applications of PMDs in otliei technical or scientific areas have additional special requirements. 

On the other hand, the luminescence quantum efficiency can decrease. Apart from a decrease of the oscillator strengths themselves, many other mechanisms can cause such reduced quantum efficiencies, as, for example, enhanced electron-phonon coupling, generation of new paths for deexcitation or energy transfer processes. In fact, these processes will not affect the oscillator strengths of the transition but simply influence the occupation of the excited level. Therefore, the oscillator strength of a given transition may still increase under pressure, however, this increase is completely covered up by a fast depletion of the excited level. 

Luminescence quantum efficiency 132 shell, nanowires, nanotubes, and other novel ... 

The absolute luminescence quantum efficiency in low defect density a-Si H samples is in the range 0.3-1 at low temperature. Thus the... 

The total luminescence intensity is the product of the number of excited electron-hole pairs and the recombination rate, N /x. If tIl is the luminescence quantum efficiency and G is the excitation intensity, then by definition, t i, G is the luminescence intensity. is the density of states which are occupied by electron-hole pairs. Since cannot be greater than the available density of states at the emission energy, then it follows from Eq. (8.30) that... 

The competition between the radiative and non-radiative rates, and Pnr, defines the luminescence quantum efficiency. 

Experimentally, the intensity of luminescence can be measured using a fluorescence spectrometer and expressed as the luminescence quantum efficiency (), defined as the ratio of the rate of luminescence to the rate of absorption (rate of light emitted/rate of light absorbed) ... 

The luminescence quantum efficiency when quencher is present is termed q and the bimolecular quenching rate constant is termed kq. 

The Stern— Volmer Equation In this experiment to determine the electron-transfer quenching rate constant, you will measure the luminescence quantum efficiency for a series of solutions having a constant concentration of Cr(phen)33+ and varying concentrations of an oxidizable quencher. By combining equation (8.16) with equation (8.18)... 

In the absence of chemical quenching, uranyl compounds have long luminescent lifetimes and high luminescent quantum efficiency [21]. Often, however, the excited state reacts chemically. The photochemistry of the ion, the most famous example of which is the uranyl oxalate actinometer, has generated an enormous body of work and been the subject of comprehensive reviews [22,23]. It can occur both in solution and in the solid state. The most common reaction is the oxidation of organic substrates. Both the photochemistry and the remarkable properties of the covalent bond, demand a satisfactory interpretation in terms of the electronic structure. 

Cr(ox)3]3" as donor to the 2T state of [Cr(bpy)3]3+ as acceptor. For the case of intrinsic luminescence quantum efficiencies of close to unity for both donor and acceptor chromophores, the quantum efficiency of the energy transfer process can be calculated from the experimental spectra according to... 

The intrinsic lifetime of the donor state, rD, and the luminescence quantum efficiency, rfD> of the donor in the absence of any acceptors are related by... 

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