Light spontaneous emission

Classic examples are the spontaneous emission of light or spontaneous radioactive decay. In chemistry, an important class of monomolecular reactions is the predissociation of metastable (excited) species. An example is the fonnation of oxygen atoms in the upper atmosphere by predissociation of electronically excited O2 molecules [12, 13 and 14] ... 

Spontaneous light emission from fresh material. For mycelium, the two data shown are scraped mycelium / mycelium on agar before scraping. cChemiluminescence activity of the extract in the presence of Fe + and H2O2. dThe extract was activated with methylamine, and then chemiluminescence activity was measured. A minus sign (—) indicates an unsuccessful quantitation due to various causes. 

When H2O2 is a necessary component of a luminescence system, it can be removed by catalase. If a luminescence system involves superoxide anion, the light emission can be quenched by destroying O2 with superoxide dismutase (SOD). The ATP cofactor usually present in the fresh extracts of the fireflies and the millipede Luminodesmus can be used up by their spontaneous luminescence reactions, eventually resulting in dark (nonluminous) extracts containing a luciferase or photoprotein. The process is, however, accompanied by a corresponding loss in the amount of luciferin or photoprotein. The use of ATPase and the elimination of Mg2+ in the extract may prevent such a loss. 

The luminescence of an excited state generally decays spontaneously along one or more separate pathways light emission (fluorescence or phosphorescence) and non-radiative decay. The collective rate constant is designated k° (lifetime r°). The excited state may also react with another entity in the solution. Such a species is called a quencher, Q. Each quencher has a characteristic bimolecular rate constant kq. The scheme and rate law are... 

Figure 9.20 Light emission (a) normal spontaneous emission produces incoherent light, and (h) stimulated emission produces coherent fight.

Datsyuk VV, Juodkazis S, Misawa H (2005) Comparison of the classical and quantum rates of spontaneous light emission in a cavity. Phys Rev A 72 025803... 

II. Correlation Function Expression for Spontaneous Light Emission... 

II. CORRELATION FUNCTION EXPRESSION FOR SPONTANEOUS LIGHT EMISSION... 

Figure 1- Liouville space diagram corresponding to the only term that contributes to the spontaneous light emission from a two-level system within the rotating-wave approximation [Eq. (2.7)]. Here ]g) and e) denote the ground and the excited states, respectively.

If the rate of spontaneous light emission is A, then the stationary intensity of fluorescence at this level of excitation is... 

Since an electron that has been promoted to the conduction band will have a greater energy than those left in the valence band, there is a possibility for the electron to lose this excess energy. The spontaneous return of electrons in the conduction band to the valance band is known as recombination, and is usually accompanied by light emission and heat (Figure 4.4). This phenomenon happens all the time for excited-state molecules. For instance, consider what happens when one supplies sodium atoms with sufficient energy to promote an electron from the 3s energy level... 

Blanco, L. A., and Garcia de Abajo, F. J. (2004). Spontaneous light emission in complex nanostructures. Physical Review B 69 205414-205411,205414-205412. 

Chen J., Shen N.H., Cheng C., Fan X.Y., Ding J.J. and Wang H.T., (2006) Tunable resonance in surface-plasmon-polariton enhanced spontaneous emission using a denser dielectric cladding, Appi. Phys. Lett. 89 051916 Paiella R., (2005) Tunable surface plasmons in coupied metaiio-dieiectric muitiple layers for light-emission efficiency enhancement, Appi. Phys. Lett. 87 111104(2005). 

The first and the second terms on the right-hand side of Eq.(32) describe a light absorption and the dynamic Stark shift, the third term — the stimulated light emission, the fourth term — the relaxation processes in the ground state, the fifth term — the Zeeman interaction, the sixth term — the repopulation by spontaneous transitions at a rate m m i the seventh term — the relaxation of the density matrix of the ground state atoms interacting with the gas in a cell, not influenced bv the radiation. 

We are discovering exciting parallels between man s experiments on earth and events in distant stars. For example, one of the heavy transuranium isotopes—californium-254, which decays by spontaneous fission with a half-life of 55 days —is now thought to account for the huge energy production in certain types of super-novae (exploding stars) whose intensity of light emission decays with a half-life of 55 days. 

The physical mechanism by which semiconductor light-emitting diodes (LEDs) emit light is spontaneous recombination of electron-hole pairs and simultaneous emission of photons. The spontaneous emission process is fundamentally different from the stimulated emission process occurring in semiconductor lasers and superluminescent LEDs. The characteristics of spontaneous emission that determine the optical properties of LEDs will be discussed in this section. 

The phenomenon of spectral narrowing is attributed to a cooperative effect in light emission, the so-called amplified spontaneous emission effect, which involves the coherent coupling of a large number of emitting sites in a polymer matrix. 

Stimulated emission depletion (STED) microscopy is another microscopy approach to overcome the diffraction limitation of light microscopy by inhibiting fluorescence outside of the focal spot [9]. In this context, fluorescence is viewed as spontaneous light emission while stimulating emission via synchronized laser... 

In the case of luciferases, the anions formed by simple deprotonation are sufficiently reactive to undergo spontaneous peroxidation with molecular oxygen. The role of the enzymes is probably concerned with the maximization of the quantum yield of light emission. 

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