Radiative decay rate applications

The fluorescence lifetimes (t determined at 580 nm) and quantum yields () of SRB were determined in water-dioxane mixtures and a series of alcohols at 25°C. The km value varied with the medium in the range of (4.1-0.7) x 10 s whereas the radiative decay rate constant (kr) was rather insensitive to the medium properties (2.8-1.7) X 10 s" . The relationship between In km and t(30) fall on a straight line and the slope value of the plot was 0.074 0.01. Therefore, the photophysical properties of SRB and Equation (20) are applicable to probing the polarity at a water/oil interface. 

When more conjugated diimine or pyridine ligands are used, the excited states of rhenium(I) carbonyl complexes can have substantial IL character. While the MLCT emission is often broad, with a lifetime in the submicrosecond to microsecond timescale, the IL emission usually has noticeable structural features, even in fluid solutions at ambient temperature. The emission lifetime is usually very long. A simple and widely applicable approach is to evaluate the ratio of the emission quantum yield and the emission lifetime (the product of the intersystem crossing efficiency and radiative decay-rate constant). Experimental values of... 

In about 2000, my laboratory started to study the interactions of fluorophores with metallic nanoparticles, both solution-based and surface-immobilized. Our findings agreed with other workers whom had observed increases in fluorescence emission coupled with a decrease in the fluorophores radiative lifetime. Subsequently, we applied classical far-field fluorescence descriptions to these experimental observations, which ultimately suggested a modification in the fluorophores s intrinsic radiative decay rate, a rate thought to be mostly unchanged and only weakly dependent on external environmental factors. This simple description, coupled with what seemed like a limitless amount of applications led to a paper published by our laboratory in 2001 entitled Metal-Enhanced Fluorescence , or MEF, a term now widely used today almost a decade later. 

Excited-State Kinetics. A principal emphasis of this chapter is concerned with how the application of hydrostatic pressures influences rates of ES processes such as those illustrated in Figure 9. In this simple model, it is assumed that electronic excitation leads efficiently to the formation of a single, bound state, which can decay by unimolecular radiative decay (rate constant kr), nonradiative decay (fc ), or chemical reaction to give products (kp). Alternatively, there may be bimolecular quenching of the ES dependent on the nature and concentration of some quencher Q (fcq [Q]). Each of these processes may be pressure dependent. 

While this technique has found its widest application in conjunction with field ionization detection, it is worth noting that it is equally useful in optical detection. In Eq. (23) we noted that with a cw rf source the optical signal corresponding to radiofrequency transition depends upon the relative radiative decay rates of the two levels, and the sensitivity decreases as the radiative decay rate of the final state. If the final state decays more slowly than the initial state, the signal is nearly proportional to the final state decay rate. In fact, if the pulsed laser excitation is used, and the rf is turned off... 

Chapter 1 introduces the basic foundations of molecular plasmonics. It is a self-contained chapter, starting with Maxwell s equations and concluding with the derivation of the radiative and non-radiative decay rates of emitting molecules near metal surfaces and nanoparticles. After this introductory chapter, the handbook is subdivided in two parts the first one describes the computational and theoretical methods of interest in molecular plasmonics, while the second is entirely dedicated to the most relevant applications and experimental techniques. Both parts contain precious contributions from international experts to ensure a plurality of points of view. 

This relation is only strictly applicable to two-level systems, such as atomic systems, where the transitions have sharp lines and in a medium of refractive index =1. The electric dipole radiation dominates the mechanism of radiative decay in molecular systems. For molecular systems in solution, Strickler and Berg proposed a modified equation that gives good results for the radiative rate [7]... 

In the last decade the Wannier exciton emission from direct band gap soniconductors was reconsidered for high count-rate and coincidence-detection scintillation applications and Cul, Hglj, Pbl2, ZnO Ga, and CdS In compounds in powder form were studied (Derenzo et al. 2002). In direct gap semiconductors a favorable combination of a smaller gap and an UV-VIS emission center based on Wannier exciton can provide high scintillation efficiency and subnanosecond radiative lifetimes due to microscopic superradiance effect (Niki 2006, Wilkinson et al. 2004). On the other hand, the Stokes shift of such emission centers is necessarily low (typically below 0.1 eV) and it prevents their usage in the bulk form due to enhanced reabsorption effect, see Figure 4.4. The ZnO Ga has shown the best combination of subnanosecond decay time and emission intensity... 

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