Green photonics

C07-0006. Will a green photon (A = 515 nm) eject an electron from a potassium surface If so, what is the maximum kinetic energy of ejected electrons ... 

Cooperative luminescence is the microscopic reverse of simultaneous pair excitation, and in Yb + involves the emission of a green photon following NIR Fy/2 Fj/2 excitation by the simultaneous relaxation of two excited ions to the ground state. In general, cooperative upconversion systems can be treated by the same rate equations as those given in Eq. (10), where now E = G, k2b = Ik -, and the cooperative luminescence rate constant is k oop = 2a Under low-power conditions, where Gsteady-state cooperative luminescence rates in the limit of a purely radiative system are described by Eqs. (29) and (30) ... 

Keep in mind that if both Er3+ and Yb3+ become excited and if Yb3+ transfers its energy, the final state of the Er3+ ion will be F7/2. This state then relaxes to the emitting state, 83/2. from which comes a green photon (about 18,400 cm-i in energy). 

The interpretations these groups give to the commented observations are very different. On one side, Xu et al. give all the responsibility to the if impurities. According to them, a first green photon excites the sample into the... 

In summary, the present ab initio calculations support the existence of pumping mechanisms involving two 19436 cm green photons which are sequentially absorbed up to a 5f 6d(t2 state of (UCU). This can lead both to blue emission from (UCle) after nonradiative decay and to blue emission from present 1102 " impurities after energy transfer and nonradiative decay. 

Because the wavelength of light that is emitted depends on the band gap of the semiconductor, the color of light produced by the LED can be controlled by appropriate choice of semiconductor. Most red LEDs are made of a mixture of GaP and GaAs. The band gap of GaP is 2.26 eV (3.62 X 10 J), which corresponds to a green photon with a wavelength of 549 nm, while GaAs has a band gap of 1.43 eV (2.29 X 10 1), which corresponds to an infrared photon with a... 

We shall watch what happens when a red or blue photon strikes a chlorophyll molecule (Figure 26.2). Green photons don t have the correct energy to be absorbed and just bounce away, which is why vegetation looks green when chlorophyll is still present. 

The intensity of bioluminescence emission is > 2 x 10 photon /s-cm in the dinoflageUate Gonyaulax and the spectmm of light emission ranges from 450—490 nm (blue) in deep sea species, 490—520 nm (green) in coastal water species, and 510—580 nm (yeUow-green) in terrestrial and freshwater species. 

Figure 12.13 Photosynthetic pigments are used hy plants and photosynthetic bacteria to capture photons of light and for electron flow from one side of a membrane to the other side. The diagram shows two such pigments that are present in bacterial reaction centers, bacteriochlorophyll (a) and ubiquinone (b). The light-absorbing parts of the molecules are shown in yellow, attached to hydrocarbon "tails" shown in green.

Figure 12.22 Schematic diagram showing the flow of excitation energy in the bacterial photosynthetic apparatus. The energy of a photon absorbed by LH2 spreads rapidly through the periplasmic ring of bacterio-chlorophyll molecules (green). Where two complexes touch in the membrane, the energy can be transmitted to an adjacent LH2 ring. From there it passes by the same mechanism to LHl and is finally transmitted to the special chlorophyll pair in the reaction center. (Adapted from W. Kiihlbrandf, Structure 3 521-525, 1995.)...

Energy imd wnvelength. A copper wire held in a flame colors the flame green. The energy of the photons of this light can be calculated from its wavelength. 

UV-Vis spectroscopy may also provide valuable information if small molecules are studied. However, the photochemical sensitivity of many sulfur-containing molecules may trigger changes in the composition of the sample during irradiation. For instance, this phenomenon has been observed in Raman spectroscopy using the blue or green hnes of an argon ion laser which sometimes decompose sensitive sulfur samples with formation of Sg [2, 3]. Reliable spectra are obtained with the red hnes of a krypton ion or a He-Ne laser as well as with the infrared photons of a Nd YAG laser. 

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