Electromagnet phosphorescence

Thomsons picture of the atom emerged from his work with cathode ray tubes. It was a milestone on the road to understanding atomic structure. But it was not the only major advance to come out of cathode ray experiments. Almost every television set in existence today is a cathode ray tube. The electrons stream from the cathode and are deflected by electromagnetic coils guided by signals from the television station. When an electron hits the televisions screen, which is coated with a phosphorescent material, it produces a dot of color. The dots form the picture you see on the screen. 

The physical basis of spectroscopy is the interaction of light with matter. The main types of interaction of electromagnetic radiation with matter are absorption, reflection, excitation-emission (fluorescence, phosphorescence, luminescence), scattering, diffraction, and photochemical reaction (absorbance and bond breaking). Radiation damage may occur. Traditionally, spectroscopy is the measurement of light intensity... 

Nuclear magnetic resonance spectroscopy is a technique that, based on the magnetic properties of nuclei, reveals information on the position of specific atoms within molecules. Other spectroscopic methods are based on the detection of fluorescence and phosphorescence (forms of light emission due to the selective excitation of atoms by previously absorbed electromagnetic radiation, rather than to the temperature of the emitter) to unveil information about the nature and the relative amount specific atoms in matter. 

Direct Photolysis. Direct photochemical reactions are due to absorption of electromagnetic energy by a pollutant. In this "primary" photochemical process, absorption of a photon promotes a molecule from its ground state to an electronically excited state. The excited molecule then either reacts to yield a photoproduct or decays (via fluorescence, phosphorescence, etc.) to its ground state. The efficiency of each of these energy conversion processes is called its "quantum yield" the law of conservation of energy requires that the primary quantum efficiencies sum to 1.0. Photochemical reactivity is thus composed of two factors the absorption spectrum, and the quantum efficiency for photochemical transformations. 

Radiative transitions (Chapter 4), which involve the emission of electromagnetic radiation as the excited molecule relaxes to the ground state. Fluorescence and phosphorescence are known collectively as luminescence. 

The most common application of photoluminescence is found in fluorescence spectroscopy. Fluorescence is the immediate release of electromagnetic energy from an excited molecule or release of the energy from the singlet state. If the emitted energy arises from the triplet state or is delayed, the process is referred to as phosphorescence. 

Watch hands that can be seen in the dark allow us to read the time without turning on a light. These watch hands typically are painted with phosphorescent paint. Like fluorescence, phosphorescence is the emission of light by a material previously hit by electromagnetic radiation. Unlike fluorescence, phosphorescence emission persists as an afterglow for some time after the radiation has stopped. The shorter end of the duration for continued light emission is 10-3 s but the process can persist for hours or days. 

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. 

Phosphorescence is the electromagnetic radiation that can accompany the transition of a molecule from an excited triplet state to a ground state singlet. Because the molecule goes from a triplet to a singlet state, its net spin must change during the emission of this radiation. The lifetimes for... 

B. Electromagnetic radiation comes directly as fluorescence and also can come as phosphorescence from the triplet state. Using Equation 4.16, we obtain... 

Figure 24-6 Photoluminescence methods (fluorescence and phosphorescence). Fluorescence and phosphorescence result from absorption of electromagnetic radiation and then dissipation of the energy by emission of radiation (a). In (b), the absorption can cause excitation of the analyte to state 1 or state 2. Once excited, the excess energy can be lost by emission of a photon (luminescence, shown as solid line) or by nonradiative processes (dashed lines). The emission occurs over all angles, and the wavelengths emitted (c) correspond to energy differences between levels. The major distinction between fluorescence and phosphorescence is the time scale of emission, with fluorescence being prompt and phosphorescence being delayed.

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