Luminescence extrinsic

Stimulated release from an electron from the trap to the collection band, followed by emissive recombination with an activator. This process is called thermoluminescence (electron release stimulated by heating) and optically stimulated luminescence (electron release stimulated by light) (Fig. 2.6d) Extrinsic luminescence, where after being excited, electrons of defect ions recombine with the ground state with luminescence emission (Fig. 2.6e) ... 

The measurement schemes for intrinsic or extrinsic luminescence in FIA or OF may be similar and... 

Extrinsic luminescence, where after being excited, electrons of defect ions recombine with the ground state with luminescence emission (Fig. 2.6e). 

In inorganic solids, luminescence spectra can be categorized as intrinsic or extrinsic. Intrinsic luminescence, which appears at elevated temperatures as a near Gauss-ian-shaped band of energies with its peak at a photon energy is due to... 

Biological Systems - The sensitivity of luminescence techniques and the use of extrinsic and intrinsic fluorescence probes have found considerable applications in biological research. Only a selection of such studies have been selected for citation. 

Luminescent emission involves radiative transitions between electronic states characteristic of the radiating substance (intrinsic or extrinsic). It is usually characterized by the decay time of the emission following removal of the excitation Fluorescence will refer here to the rapidly decaying component immediately following interruption of the excitation its rate is independent of excitation intensity and of temperature. Phosphorescence will refer to the more slowly decaying component which usually involves complex kinetics. 

Associated with item 2, above. Is the rotational relaxation barrier Imposed by the environment upon the probe molecule, as has been discussed for stllbene (90). This extrinsic barrier can be much higher than the Intrinsic barrier In Item 2, but results in the same observation of temperature dependence of luminescence of the probe except that the temperatures at which discontinuities In Arrhenius plots occur will be solvent dependent (39,90,91). 

More generally, an Auger transition can be defined as a transition in which energy is transferred from one electronic particle to another in such a way that in the final state the energy of one of the particles lies in a continuum. Auger processes can be classified as intrinsic or extrinsic. The former occur in the pure semiconductor, the latter involve electronic states of impurities like in the example in Figure 4.14. All types of luminescence transitions described in Section 3.3.9 can be quenched by Auger processes. 

In 1990, Canham observed intense visible photoluminescence (PL) from PSi at room temperature. Visible luminescence ranging from green to red in color was soon reported for other PSi samples and ascribed to quantum size effects in wires of width 3 nm (Ossicini et al, 2003). Several models of the origin of PL have been developed, from which we chose two. In the first (the defect model), the luminescence originates from carriers localized at extrinsic centers that are defects in the silicon or silicon oxide that covers the surface (Prokes, 1993). In the second model (Koch et al., 1996), absorption occurs in quantum-confined structures, but radiative recombination involves localized surface states. Either the electron, the hole, both or neither can be localized. Hence, a hierarchy of transitions is possible that explains the various emission bands of PSi. The energy difference between absorption and emission peaks is explained well in this model, because photoexcited carriers relax into surface states. The dependence of the luminescence on external factors or on the variation of the PSi chemistry is naturally accounted for by surface state changes. 

Overall, luminescent probes provide a powerful and versatile tool for studying supramolecular structures and their practical uses. Multiple intrinsic and extrinsic parameters of chemical and biological samples are measurable by their means. Accompanying multiple detection formats facilitate the collection of large amounts of information about supramolecular structures, their macro- and micro-... 

Figure 19.2 shows that the optical absorption of composites can be tuned over a very wide range of wavelengths by adding a suitable surfactant or by varying its concentration. Because of quantum confinement, variation of the mean nanoparticle size shifts the excitonic recombination band and the onset of absorption. Luminescence is dominated by extrinsic recombination and is pretty weak in as-grown samples. Typical quantum yields were well below 1%, which is typical for quantum dots grown in aqueous environment. 

---