Luminescent materials applications

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 ... 

Extended linear chain inorganic compounds have special chemical and physical properties [60,61], This has led to new developments in fields such as supramolecular chemistry, acid-base chemistry, luminescent materials, and various optoelectronic applications. Among recent examples are the developments of a vapochromic light emitting diode from linear chain Pt(II)/Pd(II) complexes [62], a luminescent switch consisting of an Au(I) dithiocarbamate complex that possesses a luminescent linear... 

Blue luminescence of zinc complexes of pyridyl-containing complexes is an area of current interest.277 Design of blue luminescent materials is of relevance to display applications, as blue-light-emitting diodes, and to this end Che examined solution luminescence of zinc pyridylamine complexes.73,278 Che and co-workers studied the complex Zn40(7-azaindoyl)6 which has a blue emission at 433 nm in the solid state.279,280 In an attempt to improve on stability Wang et al. examined compounds with neutral 7-azaindole and an A-functionalized pyridyl derivative.281 In contrast with other metal complexes of the neutral 7-azaindole (32), Zn(7-azaindole)2(OAc)2 is a blue luminescent compound and a A-(2-pyridyl) 2-azaindole (33) and its complexes were also... 

The use of doped and undoped silica aerogels as multifunctional host materials for fluorescent dyes and other luminescent materials for display and imaging applications has been reported.278 Results have been presented on the PL spectra of undoped silica aerogels and aerogels doped with Er3+, rhodamine, and fluorescein.278... 

This low-lying vacant p orbital also allows boron-containing polymers to be luminescent again signaling potential optical applications. Many of these luminescent materials are NLO materials. 

Photoluminescence is a term widely applied to the range of phenomena where light emission occurs from a material after energising by photons. In this section of the book the term is specifically applied to the cases where luminescence occurs after the interaction of luminescent materials with narrow band, higher energy ultraviolet radiation, namely in lighting and plasma display panel applications. 

Lighting. An important application of clear fused quartz is as envelop material for mercury vapor lamps (228). In addition to resistance to deformation at operating temperatures and pressures, fused quartz offers ultraviolet transmission to permit color correction. Color is corrected by coating the inside of the outer envelope of the mercury vapor lamp with phosphor (see LUMINESCENT MATERIALS). Ultraviolet light from the arc passes through the fused quartz envelope and excites the phosphor, producing a color nearer the red end of the spectrum (229). A more recent improvement is the incorporation of metal halides in the lamp (230,231). 

Chemiluminescent Immunoassay. Chemiluminescence is the emission of visible light resulting from a chemical reaction. The majority of such reactions are oxidations, using oxygen or peroxides, and among the first chemicals studied for chemiluminescence were luminol (5-amino-2,3-dihydro-1,4-phthalazinedione [521-31-3]) and its derivatives (see Luminescent materials, CHEMILUMINESCENCE). Luminol or isoluminol can be directly linked to antibodies and used in a system with peroxidase to detect specific antigens. One of the first applications of this approach was for the detection of biotin (31). 

The initial focus in dendrimer research was largely on their synthesis, but recently more importance has been given towards their functional aspects [23]. The successful blending of dendrimer chemistry with several contemporary themes such as host-guest chemistry [24], metallo-organic chemistry [25], luminescent materials [26], catalysis [20a], medicinal chemistry [18d] and polymers [27] has contributed enormously over the years to a rich chemistry with potential applications. As a detailed survey of this area is beyond the scope of this chapter, we will restrict ourselves to two topics involving these molecules (a) dendritic self-assembly [28] and (b) metallodendrimers [25,26]. 

The first optical laser, the ruby laser, was built in 1960 by Theodore Maiman. Since that time lasers have had a profound impact on many areas of science and indeed on our everyday lives. The monochromaticity, coherence, high-intensity, and widely variable pulse-duration properties of lasers have led to dramatic improvements in optical measurements of all kinds and have proven especially valuable in spectroscopic studies in chemistry and physics. Because of their robustness and high power outputs, solid-state lasers are the workhorse devices in most of these applications, either as primary sources or, via nonlinear crystals or dye media, as frequency-shifted sources. In this experiment the 1064-mn near-infrared output from a solid-state Nd YAG laser will be frequency doubled to 532 nm to serve as a fast optical pump of a raby crystal. Ruby consists of a dilute solution of chromium 3 ions in a sapphire (AI2O3) lattice and is representative of many metal ion-doped solids that are useful as solid-state lasers, phosphors, and other luminescing materials. The radiative and nonradiative relaxation processes in such systems are important in determining their emission efficiencies, and these decay paths for the electronically excited Cr ion will be examined in this experiment. 

Rare earth silicates exhibit potential applications as stable luminescent materials for phosphors, scintillators, and detectors. Silica and silicon substrates are frequently used for thin films fabrication, and their nanostructures including monodisperse sphere, NWs are also reliable templates and substrates. However, the composition, structure, and phase of rare earth silicates are rather complex, for example, there are many phases like silicate R2SiOs, disilicate R2Si207 (A-type, tetragonal), hexagonal Rx(Si04)602 oxyapatite, etc. The controlled synthesis of single-phase rare earth silicate nanomateriais can only be reached with precisely controlled experimental conditions. A number of heat treatment based routes, such as solid state reaction of rare earth oxides with silica/silicon substrate, sol-gel methods, and combustion method, as well as physical routes like pulsed laser ablation, have been applied to prepare various rare earth silicate powders and films. The optical properties of rare earth silicate nanocrystalline films and powders have been studied. 

Main group oxides with three-dimensional stmctures or transition metal oxides with d° or d ° configurations are wideband gap materials and are colorless when pure. As such they may serve as transparent optical materials or hosts for such applications as lasers or luminescent materials when properly doped. Others that lack a center of symmetry may have ferroelectric or ferroic properties that make them useful for a variety of device applications. Some of these may have nonlinear optical properties so important to modem communication networks (see Sections 6.3 and 6.5 and see Luminescence and see Ferroelectricity). 

Luminescent materials have changed the world. Energy saving lamps, many kinds of displays and modern medical equipment all rely on luminescent materials and it is hardly imaginable that large scale application of luminescent materials started only slightly more than 100 years ago (for an overview see e.g. Ref [5.198]). 

About 100 years of research on luminescent materials has resulted in phosphors with impressive maturity. In almost all applications, phosphors perform at their physical limits. We will close this section by considering two research areas, which may lead to important new application fields cascade phosphors and quantum dots. 

Taking these few examples from amongst many others, it can be seen that research on luminescent materials is still extremely challenging. Driven by both new materials and new application areas, the search for new and improved luminescent materials is an important research topic both in industry and academia. 

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