Luminescence excited cathodoluminescence

Excitation by impinging electrons (or ions) takes place by a somewhat different mechanism. Energetic electrons penetrate the phosphor grains and the lose energy by multiple collision processes. The energy is sufficient to pump the conduction band of the phosphor host and the excitation can move anywhere in the crystal to pump the localized luminescence centers. Cathodoluminescence thus appears at lower concentration thresholds than photoluminescence but is more susceptible to the influence of defects and other luminescence poisons. 

Depending on the excitation method used, luminescence techniques are divided into photoluminescence excited by photons, cathodoluminescence generated under the action of cathode rays, X-ray luminescence excited by X-rays, candoluminescence generated under the action of heat, and sonoluminescence excited by ultrasound. Emission generated under the action of a stream of ions from alkali metals in vaccum is called ionoluminescence radiation which atoms emit on optical excitation in plasma is known as atomic fluorescence chemiluminescence is the emission of radiation generated by the energy of chemical reactions, it does not require an external excitation source. The excitation source needed in each particular case is chosen on the basis of this classification. 

Cathodoluminescence is the luminescence observed upon excitation by high-energy electrons. 

A luminescent mineral is a sohd, which converts certain types of energy into electromagnetic radiation over and above thermal radiation. The electromagnetic radiation emitted by a luminescent mineral is usually in the visible range, but can also occur in the ultraviolet (UV) or infrared (IR) range. It is possible to excite the luminescence of minerals by UV and visible radiation (photoluminescence), by a beam of energetic electrons (cathodoluminescence), by X-rays (X-ray excited luminescence) and so on. A special case is so-called thermoluminescence, which is stimulation by the heating of luminescence, prehminary excited in a different way. 

A possible candidate may be Tm ". For example, the doublets at 803 and 817 nm and at 796 and 813 nm are the strongest ones in cathodoluminescence spectra of fluorite and scheelite activated by Tm " (Blank et al. 2000). It is possible to suppose that the strong fines at 805 and 820 nm with a relatively short decay time of 60 ps in the titanite luminescence spectrum belong to Tm " ". They appear under 532 nm excitation and are evidently connected with the electron transition. Similar emission of Tm " was also detected in... 

Energy Transfer Processes. Luminescence is a complex sequence of energy transfer processes. Figure 2 is a schematic of the most important of these for photoluminescence, cathodoluminescence, and candoluminescence. The ultimate source of energy is the excitation UV light, electron beam, ion beam, or radical recombination excitation. We are not concerned here about the triggered release of previously trapped energy such as occurs in thermoluminescence and triboluminescence. 

Shionoya S, Yen WM (1999) Phosphor Handbook. CRC Press, Boca Raton, Florida Smith JV, Stenstrom RC (1965) Electron-excited luminescence as a petrologic tool. J Geol 73 627-635 Stefanos SM, Bonner CE, Meegoda C, Rodriguez WJ, Loutts GB (2000) Energy levels and optical properties of neodymium-doped barium fluorapatite. J Appl Phys 88 1935-1942 Solomonov VI, Osipov VV, Mikhailov SG (1993) Pulse-periodic cathodoluminescence of apatite. Zh Prikladnoi Spectroskopii 59 107-113... 

Cathodoluminescence (CL) Luminescence produced by excitation by an incident beam of electrons. 

A phosphor screen is used to convert electron energy into radiant energy in a CRT display device. The screen is composed of a thin layer of luminescent crystals, phosphors, that emit Kght when bombarded by electrons. This property is referred to as cathodoluminescence. It occurs when the energy of the electron beam is transferred to electrons in the phosphor crystal. The property of Kght emission during excitation is termed fluorescence, and that immediately after excitation is removed is termed phosphorescence. 

Optical Properties of Clusters. Recently optical luminescence of InP clusters has revealed surprisingly narrow (less than one millielectron volt) spectral lines (55). Photoluminescence and cathodoluminescence has been used at the University of Lund, Sweden to excite InP imbedded between layers of GalnP (Carlsson, N. Seifert, W. Petersson, A. Castrillo, P. Pistol, M. E. and Samuelson, L., to be publishe<. STM has been used to excite some of these materials (56). The strained InP layer wifh approximately 10 monolayers of thickness spontaneously reforms into 100 nm quantum dot structures. These quantum dots luminesce at 1.6 to 1.85 eV and have demonstrated line widths of less than 0.1 meV at 77 K. 

The active participation of Sq level is indirectly accredited by the simultaneous observation of UV and visible emission in cathodoluminescence and synchrotron excited spectra (Fig. 5.8) Excitation into the 4f5d and higher lying bands evidently decays to the Sq level located at 46,300 cm which exhibits luminescence in wide band-gap hosts due to radiative de-excitation to the lower lying levels of Pr. The So- F4 transition at 246 nm is especially strong in oxyapatite. In F-apatite only the line at 269 nm is present. It may be explained by the relatively long-waved absorption edge in fluorapatite, which is at about 300 nm (Morozov et al. 1970). 

The book deals mainly with theoretical approach, experimental results and their interpretation of laser-induced time-resolved spectroscopy of minerals in the wide spectral range from 250 to 2000 nm, which enables to reveal new luminescence previously hidden by more intensive centers. Artificial activation by potential luminescence centers has been accomplished in many cases, which makes the sure identification possible. The mostly striking example is mineral apatite, which has been extremely well studied by many scientists using practically all known varieties of steady-state luminescence spectroscopy photoluminescence with lamp and laser excitations. X-ray excited luminescence, cathodoluminescence, ionolumi-nescence and thermoluminescence. Nevertheless, time-resolved spectroscopy revealed that approximately 50 % of luminescence information remained hidden. The mostly important new information is connected with luminescence of trivalent... 

The main luminescence bands found in cBN crystals are summarized in Table 8 and Fig. 34. In most cases, the luminescence is excited by electron beams (cathodoluminescence, CL) (185-198). Luminescence caused by recombination of electrons and holes in pn junctions (injection luminescence, IL) has been observed (189,199). The origin of any of the luminescence bands is unknown at present, although there are discussions in the literature. 

Electroluminescence is light emission initiated by electric influences. For example, in cathodoluminescence, the emission of light is initiated by excitation with an electron beam. Radioluminescence is caused by excitation with nnclear radiation or X-rays, whereas tribo-luminescence occurs when certain materials are mechanically altered, such as when fractured or polished. 

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