Lanthanides fluorescence lifetimes

Figure 2-17. Time-resolved fluorescence. Chelate complexes of many lanthanides show unusual fluorescence behaviour in that there is a large separation between the fluorescence excitation and emission maxima, and also extremely long fluorescence lifetimes. This enables...

The spectroscopic properties and chemistry of aprotic Nd + laser liquids plus references to earlier studies are discussed by Brecher and French (V7). The oscillator strengths and fluorescence lifetimes are comparable to those in solids with quantum efficiencies near unity. Since fluorescence line-widths are smaller than in glasses, the stimulated emission cross sections are larger (1 8), although still less than in crystals. Aprotic liquid laser materials and references are listed in Ref. 19. Thus far only Nd3+ has been used as the laser ion although other lanthanide ions could also be used. 

Fluorescence studies. The fluorescence yield and the fluorescent lifetimes of lanthanide cations in solution are functions of the nature and arrangement of the species associated with the metal in its primary coordination sphere. Based on their fluorescent properties, these elements have been classified into three categories (Crosby 1966, Whan and Crosby 1962, Sioni and Lovgren 1987)... 

Keywords Autofluorescence Decay time Delayed fluorescence Fluorescence lifetime imaging microscopy Lanthanides Phosphorescence Time-correlated single photon counting Time-resolved fluorescence microscopy... 

Alkaline-earth fluoride crystals have been the principal hosts for divalent lanthanide laser ions. These are relatively soft, optically isotropic materials. Rare earths occupy cubic Ca sites. The allowed radiative transitions between 4f states are magnetic-dipole or vibronic. Since these are relatively weak, the fluorescence lifetimes are long, —10 ms. In comparison, the fluorescence lifetime of the 5d 4f transition of SrF2 Sm, which is electric-dipole allowed, is short,... 

The time-dependent methods, which are unaffected by or less sensitive to the complications that intensity measurements suffer, include the time domain (time-resolved) technique, in which the fluorescence decay lifetime x is measured, and the frequency domain technique, in which the frequency response of donor emission is used to obtain interprobe distances (distribution). Each requires highly specialized, high-cost, instruments, often custom-built for nanosecond lifetime measurement before the lanthanide probes were developed. In the time-resolved method, E = 1 - Tda/ d, where Tda and Td are donor fluorescence lifetime in the presence and absence of an acceptor, respectively. For the purpose of studying structure-function relations of macromolecules, the accurate measure of absolute distance is of less importance and interest than the changes in distance in response to condition changes. 

Homogeneous Time Resolved Fluorescence (HTRF) (Cisbio International) is an assay based on the proximity of a lanthanide cryptate donor and a fluorescent acceptor molecule whose excitation wavelength overlaps that of the cryptate s emission. The utility of this technique is based on the time resolved fluorescence properties of lanthanides. Lanthanides are unique in the increased lifetime of their fluorescence decay relative to other atoms, so a delay in collection of the emission intensity removes the background from other fluorescent molecules. An example of the HTRF assay is a generic protein-protein interaction assay shown in Fig. 2. 

---