Short-wavelength ultraviolet rays

X rays comprise that portion of the electromagnetic spectrum which lies between ultraviolet and gamma rays. The range of wavelengths is typically from about 0.01 to 100 A. Because of their very short wavelengths, X rays are powerful probes of atomic structure. 

The term smart material is now used for a rather wide variety of materials, some that have been known and used for many years and some that have been developed only recently. For example, phosphorescent and fluorescent materials are familiar and widely used materials that are sometimes defined as smart materials because they have the capacity to absorb electromagnetic radiation of short wavelengths (X-rays or ultraviolet rays, for example) and re-emit that radiation in the form of visible light. The difference between phosphorescence and fluorescence is that a phosphorescent material continues to emit light after radiation has ceased, while the emission of fluoresced light ends as soon as the source of radiation is removed. 

Ozone (O3) is a colorless gas at ambient temperature and pressure and has a characteristic odor even at very low concentrations. It has a strong oxidizing ability that is hazardous to plants and animals, and is unstable especially at higher concentrations. Electric discharge in oxygen (or air) and irradiation of oxygen (air) with short-wavelength ultraviolet (UV) rays produce ozone. 

In some fluorides (e.g. YF3, LaFs, NaYF4) the lowest crystal-field component of the 4f5d state of Pr is situated above the So level. Excitation with short-wavelength ultraviolet radiation (e.g. 185 nm) or cathode-rays excites the Pr + ion from the H4 ground state into the 4f5d level, from where it decays radiationless to the So level. From here the Pr ion returns to the ground state by two-photon luminescence (Piper et al., 1974, Sommerdijk et al., 1974a) the... 

One of the most direct methods is photoelectron spectroscopy (PES), an adaptation of the photoelectric effect (Section 1.2). A photoelectron spectrometer (see illustration below) contains a source of high-frequency, short-wavelength radiation. Ultraviolet radiation is used most often for molecules, but x-rays are used to explore orbitals buried deeply inside solids. Photons in both frequency ranges have so much energy that they can eject electrons from the molecular orbitals they occupy. 

When radiation of sufficiently short wavelength interacts with matter, ( electrons are emitted. This is the photoelectric effect. It can be observed in gases and solids, and with X-rays and y rays, as well as with ultraviolet j radiation. It was die phenomena observed with short-wavelength visible and < ultraviolet radiation on solids, however, which were known in 1905. Figure J 1.10 shows the apparatus used. Light or UV radiation falls on one electrode 4 in an evacuated tube. If electrons are emitted, some will reach the second <... 

Figure 17.1 Sunlight is simply electromagnetic radiation that our eyes detect. The wavelengths in this fraction of the spectrum are shown as the vertical letters Vis. This chart of the electromagnetic spectrum also shows waves with shorter wavelengths (ultraviolet, X-rays, and gamma rays) as well as longer wavelengths (infrared, microwaves, short radio waves (TW/EM), and longer radio waves).

The azonitriles may also be used as initiators in photopolymerizations, in which case free radicals are formed at temperatures in the neighborhood of O C upon irradiation with rays of short wavelength in the visible or neaiv ultraviolet region. 

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