Energy transfer from irradiated solids

Fig. 35 Photoinduced surface potential change under step illumination at 441.5 nm (solid curve) or 325 nm (dotted curve). The S moiety of the triad is directly excited by the 441.6 nm irradiation, whereas at 325 nm, the excited state S is induced via energy transfer from H. ...

Figure 1 shows the ultraviolet (UV) spectra of an unexposed MP2400-17 film and a film exposed to 470 mJ/cm. The films were spin coated onto quartz substrates and baked at 90 C for 30 minutes in a forced-air oven. The film thickness after baking was 0.465 bm. Exposure was accomplished by direct irradiation of the film to the narrowed output of a Math Sciences EXL-100 KrF excimer laser. Thirty pulses were delivered at an average dose of 15.7 mj/cm per pulse. The spectrum of the quartz substrate was automatically subtracted from the spectra of the films on the substrates to obtain Figure 1. The absorbance of the two films is the same at wavelengths below 310 nm and the solid curve in Figure 1 represents the absorbance of both films. The absorbance at 248 nm is 0.49 for both films. Destruction of the PAG by the 248 nm radiation, as evidenced by the disappearance of the longer wavelength absorption in the irradiated film, presumably occurs after nonradiative energy transfer.

The radiative deactivation of excited states in polymers has found widespread application in the field of plastic scintillators. Most of the knowledge on light emission during irradiation results from research performed in the years 1950—1965 to achieve the optimum scintillation efficiency of solid polymer systems. The ionizing radiation is absorbed in a polymer, usually polystyrene, and produces excited states which are transferred with a high yield to a fluorescent solute. The theory of excitation transfer will be developed in Chapter 3. If the energy donor is P and the fluorescent solute S, competition between energy transfer to S... 

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