Quantum efficiency, spectral parameters

The most important parameters of the photolumincsccnce spectrum which are necessary to identify the emitting species are its spectral shape, from which the emission intensity 4 is obtained as a function of wavelength A its quantum efficiency e, by which the intensity is measured relative to the absorption photointensity /a and its lifetime t, determined from the decay curves of variation of the intensity measured as a function of time (33, 34, 36-38, 49-53). 

It is more difficult to fabricate semitransparent than opaque devices because the thickness of the sensitive layer is an added critical parameter not important in the opaque structure. (Improper thickness in the semitransparent device would limit both the range of useful spectral response and overall quantum efficiency [5.29].) Most new photoemissive surfaces, particularly NBA, are now investigated initially in their opaque ( reflection mode , RM , or front illuminated ) form, which usually offers the highest initial optical and electron-emissive quantum efficiency, and only after determining optimum thickness and optimum fabrication methods are new surfaces produced in the semitransparent ( transparent , transmission mode , TM , or back illuminated ) form. Eventually both forms are offered commercially in several variants, each optimized for selected parameters such as low cost, peak response at a specific... 

Among other parameters the external quantum efficiency (EQE) can be estimated. EQE is defined as a ratio of the number of electrons in external circuit to the number of incident photons. To evaluate the EQE one measures the spectral response (SR) of the photovoltaic device (PVD) ... 

Furthermore, a cw-EPR spectrum can be simulated based on quantum mechanics. The most widely used approach in EPR spectral simulation is based on the stochastic Liouville equation (SLE), which treats the electronic and nuclear spins quantum mechanically, while the nitroxide re-orientation motion is treated classically and parameterized in terms of rotational diffusion constants. The SLE approach is extremely efficient and capable of computing a spectrum in a fraction of a second. This enables iterative fitting of experimental spectra, including those that fall within the slow-motion regime. " However, SLE-based spectral simulations depend on the physical model used to describe the nitroxide motion, which usually requires a large number of parameters, and unique determination of nitroxide motion from simulation remains challenging. 

---