Metal-enhanced fluorescence absorption process

Figure 1.2. (A) A schematic diagram depicting the processes in close proximity to metals (< 10 nm) involved in Metal-Enhanced Fluorescence enhanced absorption and coupling to surface piasmons. (B) Emission spectra of FITC deposited onto SIFs and glass. The inset shows the real-color photographs of FITC emission from these surfaces. (C) Intensity decays for FITC on both glass and SiFs. IRF Instrument Response Function.

Enhanced fluorescence, or MEF, is a result of both a net system absorption and plasmon coupling and subsequently efficient emission, but to date, it has not been possible to quantify the relative contributions of enhanced emission and net increase in the system absorption to the MEF phenomena.(23) Due to the increase in the population of the singlet excited state or net system absorption, the very presence of MEP has also suggests an increase in the population of the triplet state.(23) The presence of Metal-Enhanced Fluorescence, Phosphorescence, Metal-Enhanced singlet oxygen and superoxide anion radical generation in the same system is an effect of the enhanced absorption and emission effects of the fluorophores near-to silver, although these processes are effectively competitive and ultimately provide a route for deactivation of electronic excited states. 

Figure 16.3 Modified Jablonski diagram ows the energy absorption effects of near metal surface enhanced fluorescence. The process involves o eating an excited electronic singlet state by optical absorption and subsequent emission of fluorescence with different decay paths.

While the linear absorption and nonlinear optical properties of certain dendrimer nanocomposites have evolved substantially and show strong potential for future applications, the physical processes governing the emission properties in these systems is a subject of recent high interest. It is still not completely understood how emission in metal nanocomposites originates and how this relates to their (CW) optical spectra. As stated above, the emission properties in bulk metals are very weak. However, there are some processes associated with a small particle size (such as local field enhancement [108], surface effects [29], quantum confinement [109]) which could lead in general to the enhancement of the fluorescence efficiency as compared to bulk metal and make the fluorescence signal well detectable [110, 111]. 

Fluorescence (which is a special case of luminescence) in the vicinity of plas-monic metal can be both surface-enhanced and surface-quenched (Weitz et al. 1983). The fluorescence is a stepwise process involving first absorption which is enhanced by EM mechanism. For the second step (emission), the presence of metal... 

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