Luminescent phenomena applications

Chemical luminescence analysis is an important application of the luminescence phenomenon in practice. Naturally, the development of new luminescence techniques... 

Cathodoluminescence (CL), i.e., the emission of light as the result of electron-beam bombardment, was first reported in the middle of the nineteenth century in experiments in evacuated glass tubes. The tubes were found to emit light when an electron beam (cathode ray) struck the glass, and subsequendy this phenomenon led to the discovery of the electron. Currendy, cathodoluminescence is widely used in cathode-ray tube-based (CRT) instruments (e.g., oscilloscopes, television and computer terminals) and in electron microscope fluorescent screens. With the developments of electron microscopy techniques (see the articles on SEM, STEM and TEM) in the last several decades, CL microscopy and spectroscopy have emerged as powerfirl tools for the microcharacterization of the electronic propenies of luminescent materials, attaining spatial resolutions on the order of 1 pm and less. Major applications of CL analysis techniques include ... 

Luminescence can be defined as the emission of light (intended in the broader sense of ultraviolet, visible, or near infrared radiation) by electronic excited states of atoms or molecules. Luminescence is an important phenomenon from a basic viewpoint (e.g., for monitoring excited state behavior) [1] as well as for applications (lasers, displays, sensors, etc.) [2,3]. 

The method of exchange-luminescence [46, 47] is based on the phenomenon of energy transfer from the metastable levels of EEPs to the resonance levels of atoms and molecules of de-exciter. The EEP concentration in this case is evaluated by the intensity of de-exciter luminescence. This technique features sensitivity up to-10 particle/cm, but its application is limited by flow system having a high flow velocity, with which the counterdiffusion phenomenon may be neglected. Moreover, this technique permits EEP concentration to be estimated only at a fixed point of the setup, a factor that interferes much with the survey of heterogeneous processes associated with taking measurements of EEP spatial distribution. 

Circular polarized luminescence (CPL) is not covered in this book because the field of application of this phenomenon is limited to chiral systems that emit different amounts of left and right circularly polarized light. Nevertheless, it is worth mentioning that... 

The use of fluorescent dyes in biological probes and sensors is covered in some detail in Chapter 3 (section 3.5.6). Because there are marked solvatochromic effects on the luminescent spectra of many fluorophores, this phenomenon is utilised to tune their performance and application in biological and other systems. 

The same laboratory describes a group of complexes with a unique property among metal complexes, referred to as luminescence tribochromism [39], which is a substantial change in the emission of the solid upon application of pressure. This phenomenon contrasts with the more common triboluminescence, which refers to the transient emission seen upon sample grinding or crushing. In this case, the effect was observed in a set of complexes of formula [Au2( J.-TU)((j,-dppm)]Y and [Au2( i-MeTU)( i-dppm)]Y (TU = 2-thiouracyl MeTU = 6-methyl-2-thiouracyl Y = CF3COOT NCV, CKV, Au(CN)2 ). 

Our motivation for offering a further consideration of excimer fluorescence is that it is a significant feature of the luminescence behavior of virtually all aryl vinyl polymers. Although early research was almost entirely devoted to understanding the intrinsic properties of the excimer complex, more recent efforts have been directed at application of the phenomenon to solution of problems in polymer physics and chemistry. Thus, it seems an appropriate time to evaluate existing information about the photophysical processes and structural considerations which may influence excimer formation and stability. This should help clarify both the power and limitations of the excimer as a molecular probe of polymer structure and dynamics. 

Certain compounds, whether present in solution or in solid state (as molecular or ionic crystals) emit light when they are excited by photons in the visible or near ultraviolet domain of the spectrum. This phenomenon, called luminescence, is the basis of fluorimetry, a very selective and sensitive analysis technique. The corresponding measurements are made with fluorimeters or spectrofluorimeters and, for chromatographic applications, with fluorescence detectors. 

As mentioned earher, one distinct advantage of using the Ln elements is to harness their unique optical features, namely, luminescence. Indeed, there are countless examples of this very phenomenon within the hterature, with feasible applications in display technologies or sensors. Most of the luminescence studies done on these materials are usually based on Eu + or Tb emission (25,30,161,179). The reason for concentrating on these two ions is due to the ease with which they can be sensitized by an aromatic organic linker. Just the same, other lanthanides have been studied in these systems, including Dy + (180), Ho (181), (181), Pr (182), and Gd (24). Additionally, certain crystal... 

The previous chapters presented an outline of the phenomenon of luminescence in solids. They form the background for the following chapters which discuss luminescent materials for several applications, viz. lighting (Chapter 6), television (Chapter 7), X-ray phosphors and scintillators (Chapters 8 and 9), and other less-general applications (Chapter 10). These chapters will be subdivided as follows ... 

X-ray phosphors can be defined as materials which absorb X rays and convert the absorbed energy efficiently into luminescence, in practice often ultraviolet or visible emission. In this paragraph we consider the phenomenon of X-ray absorption, and the principles of some important ways of X-ray imaging and the requirements which X-ray phosphors have to satisfy in order to be promising for potential application. 

The stoted energy can be released by thermal or optical stimulation. In the case of thermal stimulation the irradiated phosphor is heated to a temperature at which the energy barrier AE can be overcome thermally. The trapped electron (or hole) can escape irom the trap and recombine with the trapped hole (or electron). In the case of radiative recombination, luminescence is observed which is called thermally stimulated luminescence (TSL) (compare Sect. 3.5). Under optical stimulation the energy of an incident photon is used to overcome AE. The luminescence due to optical stimulation is called photostimulated lumine.scence (PSL). The phenomenon of stimulated luminescence from storage phosphors has been known since 1663 (Boyle). Storage phosphors have found a wide range of applications, e.g. as infrared detectors and in the field of dosimetry [3J. 

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