Intrinsic emission efficiency

In the case of lanthanides, foUowing direct excitation of the metal ion, the efficiency of emission is called the intrinsic emission efficiency which is directly related to the overall rate at which the emissive state is depopulated through radiative/ and non-radiative NR pathways, and the radiative rate constant, k/, or their corresponding... 

Equation 1.72 above relates the radiative lifetime to the magnetic dipole-allowed transition of Eu(III). It is therefore straightforward to determine experimentally, for this ion, tr and therefore the intrinsic emission efficiency. 

A second problem is that the formation of defects that lower the emission efficiency is intrinsic in the polymerization process due to nonregular coupling of the quinodimethane intermediates, as illustrated in Scheme 6.5 for the Gilch synthesis. This has been demonstrated by NMR studies on a 13C-labelled PPV derivative, in which the ethyne and ethane moieties could be detected in 1.5-2.2% amount [38-40], By appropriate choice of substituents the levels of these defects can be minimized to obtain high-efficiency polymers [41]. 

The technical specifications of these monitors are impressive they luminesce in the entire visible spectrum, they are bright and efficient. They are thinner and lighter than LCD monitors (liquid crystal displays) and are therefore especially suited for portable equipment. They are intrinsically emissive, and thus require no background illumination, and they have a display angle of nearly 180°. Furthermore, they are fast and thus suitable for rapid video sequences. The image points (pixels) can be switched to a completely dark state, so that higher contrast can be obtained. 

This section describes the enhancement of emission efficiency and sensitivity of the QD-nanopore array system before going on to review monotonic sensing and intrinsic PL responses. A final section discusses enhanced sensing stability and the results of core vs. core-shell studies. 

Silsesquioxane-based hybrid materials were also used to produce pure color emission, as the following examples illustrate. Red emission was produced by doping urea-based polysilsesquioxanes (Si-BSA, Figure 28.3) with Safranin O [89]. The absence of the blue-green intrinsic emission of the diureasil host indicates an efficient hybrid-to-dye energy transfer [89]. 

Luminescence measurements on proteins occupy a large part of the biochemical literature. In what surely was one of the earliest scientific reports of protein photoluminescence uncomplicated by concurrent insect or microorganism luminescence, Beccari (64), in 1746, detected a visible blue phosphorescence from chilled hands when they were brought into a dark room after exposure to sunlight. Stokes (10) remarked that the dark (ultraviolet) portion of the solar spectrum was most efficient in generating fluorescent emission and identified fluorescence from animal matter in 1852. In general, intrinsic protein fluorescence predominantly occurs between 300 nm and 400 nm and is very difficult to detect visually. The first... 

In addition to the surface/interface selectivity, IR-Visible SFG spectroscopy provides a number of attractive features since it is a coherent process (i) Detection efficiency is very high because the angle of emission of SFG light is strictly determined by the momentum conservation of the two incident beams, together with the fact that SFG can be detected by a photomultiplier (PMT) or CCD, which are the most efficient light detectors, because the SFG beam is in the visible region, (ii) The polarization feature that NLO intrinsically provides enables us to obtain information about a conformational and lateral order of adsorbed molecules on a flat surface, which cannot be obtained by traditional vibrational spectroscopy [29-32]. (iii) A pump and SFG probe measurement can be used for an ultra-fast dynamics study with a time-resolution determined by the incident laser pulses [33-37]. (iv) As a photon-in/photon-out method, SFG is applicable to essentially any system as long as one side of the interface is optically transparent. 

INTRINSIC AND EXTRINSIC FLUORESCENCE. Intrinsic fluorescence refers to the fluorescence of the macromolecule itself, and in the case of proteins this typically involves emission from tyrosinyl and tryptopha-nyl residues, with the latter dominating if excitation is carried out at 280 nm. The distance for tyrosine-to-tryp-tophan resonance energy transfer is approximately 14 A, suggesting that this mode of tyrosine fluorescence quenching should occur efficiently in most proteins. Moreover, tyrosine fluorescence is quenched whenever nearby bases (such as carboxylate anions) accept the phenolic proton of tyrosine during the excited state lifetime. To examine tryptophan fluorescence only, one typically excites at 295 nm, where tyrosine weakly absorbs. [Note While the phenolate ion of tyrosine absorbs around 293 nm, its high pXa of 10-11 in proteins typically renders its concentration too low to be of practical concern.] The tryptophan emission is maximal at 340-350 nm, depending on the local environment around this intrinsic fluorophore. 

FRET interactions are typically characterized by either steady-state or transient fluorescence emission signals from the donor or acceptor species. Efficient nonradiative energy transfer results in donor PL loss associated with acceptor gain in photoluminescence intensity (if the acceptor is an emitter). The rate of this energy transfer is related to the intrinsic lifetime of the isolated donor and depends strongly on the donor-acceptor separation distance ... 

To be used in x-ray intensifying screens, rare earth phosphors must also have high conversion efficiencies (nc Figure 1) in addition to high intrinsic absorptions of x-rays and suitable emission characteristics. The several rare earth phosphors listed in Table I have conversion efficiencies from about 10% for La202S Tb to about 20% for LaOBr Tb (5,, ) as compared to about 6% for CaWOi. ... 

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