Scintillation phosphors applications

Finally, with their spatial resolution only limited by the channel dimensions and the spacing between channels (typically both of the order 10—20 pm), they are ideally suited for imaging applications. For this, the electron flux exiting from the MCP impinges on a scintillator (phosphor) plate, which in turn is coupled to a 2D CCD sensor recording the spatial distribution of the scintillator excitation. All three components are mounted in close proximity to maintain the micrometre resolution, as shown in Figure 13.14c. Such detectors are used in the electron-and ion-imaging experiments described, for example, in Chapter 23. 

The cadmium chalcogenide semiconductors (qv) have found numerous applications ranging from rectifiers to photoconductive detectors in smoke alarms. Many Cd compounds, eg, sulfide, tungstate, selenide, telluride, and oxide, are used as phosphors in luminescent screens and scintillation counters. Glass colored with cadmium sulfoselenides is used as a color filter in spectroscopy and has recendy attracted attention as a third-order, nonlinear optical switching material (see NONLINEAR OPTICAL MATERIALS). Dialkylcadmium compounds are polymerization catalysts for production of poly (vinyl chloride) (PVC), poly(vinyl acetate) (PVA), and poly(methyl methacrylate) (PMMA). Mixed with TiCl4, they catalyze the polymerization of ethylene and propylene. 

Scintillation counters are used to detect energy-rich particles and y rays. They consist of a combination of a phosphor, usually a single crystal, with a photomultiplier or a photodiode as detector. Alkali-metal iodides (see Table 56), Bi4Ge3012, CaW04, ZnW04, CdW04, and ZnS Ag+, Ni+ are typical phosphors for this application [5.438]. 

Many applications of lanthanide materials make use of the 4f 15d excited configuration. These applications include scintillator materials, VUV lasers, and phosphors for fluorescent lighting and plasma displays (Blasse and Grabmaier, 1994 Feldmann et al., 2003). An understanding of these states is crucial to the development of advanced materials. 

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. 

The phosphor Tb +iInBOs has been promoted as a green phosphor in cathode-ray tubes and as a possible scintillator. It exhibits a quantum efficiency under cathode-ray excitation of 8%, and it is stable to intense electron beams. The emission lifetime of 7.5 ms, however, is likely to be too long for some applications. 

Luminescent oxides (or phosphors) play an important role in television receivers and other cathode ray tube (CRT) applications, fluorescent lamps, scintillation counters, and information display devices including CRT and flat panel display (FPD) as well as the emerging plasma display... 

Ceramics in aluminate systems are usually formed from cubic crystal systems and this includes spinel and garnet. Rare earth aluminate garnets include the phase YAG (yttrium aluminium garnet), which is an important laser host when doped with Nd(III) and more recently Yb(III). Associated applications include applications as scintillators and phosphors. 

The next subject we will address is that of scintillators. These are phosphors used to detect a, p, and y rays from incident sources. This application has become very important with the advent of CT-scanners and the PET-scanner, i.e.- CT = "computerized tomagraphy" and PET = "positron emission tomography". In all cases, radioactive Isotopes are used as the source of these "rays", including positrons, i.e.- positive electrons, p. Although scintillation, i.e.- detection of high energy radioactive-decay particles, may occur for nearly all phosphors, efficient scintillators must satisfy the following requirements for practical use. 

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 ... 

The terms X-ray phosphors and scintillators are often used in an interchangeable way. Some authors use the term X-ray phosphors when the application requires a powder screen, and the term scintillator when a single crystal is required. The physical processes in the luminescence of these two types of materials is, however, in principle the same and comparable to that in cathode ray phosphors (Chapter 7). 

Part three consists of five chapters in which many of the applications are discussed, viz. lighting (chapter 6), cathode-ray tubes (chapter 7), X-ray phosphors and scintillators (chapters 8 and 9), and several other applications (chapter 10). These chapters discuss the luminescent materials which have been, are or may be used in the applications concerned. Their performance is discussed in terms of the theoretical models presented in earlier chapters. In addition, the principles of the application and the preparation of the materials are dealt with briefly. Appendices on some, often not-well-understood, issues follow (nomenclature, spectral units, literature, emission spectra). 

Some of the compounds mentioned in Section 4.3 exhibit luminescence under UV or ionizing radiation or accelerated particle-beam exposures that can be used in related applications as phosphor or scintillator materials (Blasse and Grabmeier 1994, Shionoya and Yen 1998). 

Apart from the applications mentioned earlier, it is worth mentioning the extended usage of YAG Ce and derived compositions in phosphors for white light LED, which in the last decade gave way to a new generation of solid-state lighting, see reviews Wu et al. (2007) and Ye et al. (2010) and references therein. Also a ceramic version of YAG Ce has been reported for such an application recently (Nishiura et al. 2011). Scintillation ceramics prepared from nanopowder precursors and... 

Luminescent solid-state materials comprised of insulating host lattices (normally oxides, fluorides, nitrides, and oxy-nitrides) activated by rare-earth and transition-metal ions continue to be an active area of research due to their application as phosphors, scintillators, and functional materials. 

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