Cathode ray excitation

Emission Spectra. High resolution emission spectra were obtained using cathode ray excitation. For this purpose, phosphor powders were uniformly settled on conductive glass. The samples were excited in a demountable cathode ray apparatus with 10 kilovolts and 7 microampere energetic electrons. The demountable apparatus was coupled to a Cary 14 spectrophotometer for recording of the emission spectra. 

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. 

What this means is that these UV-radiation wavelengths will excite the phosphor which then emits visible green light. When the phosphor is prefired in air, the resulting phosphor does not respond to UV excitation. However, cathode-ray excitation (an electron-beam like a television tube) produces the same green emission. Emission occurs from Mn centers in the spinel structure. These centers are not Intrinsic defects as such since the divalent manganese is able to substitute directly at the Mg sites in the spinel structure. The only difference is the radius of the two cations at the tetrahedral site. It is because of this difference that increasing the Mn concentration leads to less efficient, i.e.- "duller , phosphors. 

From this discussion, it should be obvious that the two most important properties of cathode-ray phosphors are the response to electron-beaun excitation (brightness) and the decay time. We require a long-decay phosphor for radar applications and a short-decay phosphor for television usage. Nearly all the cathode-ray phosphors are based on the zinc and cadmium sulfides because they exhibit the highest efficiency to cathode-ray excitation. ZnS forms a series of solid solutions with CdS whose emission band can be shifted from the blue (ZnS Ag) to the red phosphor. 

ITie host lattices which yield the highest radiant efficiency (Sect 4.3) for cathode-ray excitation are undoubtedly ZnS and its derivatives. For the blue-emitting ZnS Ag values higher than 20% have been reported. We note that this fits our discussion in Sect. 4.4, where the maximum efficiency for host lattice excitation was found to occur for small values of the band gap Eg and the vibrational frequency i lo (Eqs (4.5)-(4.7)). For ZnS Eg = 3.8 eV and I l.o = 350 cm . These values satisfy our requirements. This can be illustrated by Y2O3 with Eg = 5.6 eV and i>lo 550 cm", yielding a maximum efficiency of only 8%. Although the latter value is for red emission, this value is much lower than for ZnS. 

Mg. 7.11. Emission spectra of fi- and y-Y2Sii07 Cc under cathode-ray excitation (after Ref. (13])... 

In some fluorides (e.g. YF3, LaFs, NaYF4) the lowest crystal-field component of the 4f5d state of Pr is situated above the So level. Excitation with short-wavelength ultraviolet radiation (e.g. 185 nm) or cathode-rays excites the Pr + ion from the H4 ground state into the 4f5d level, from where it decays radiationless to the So level. From here the Pr ion returns to the ground state by two-photon luminescence (Piper et al., 1974, Sommerdijk et al., 1974a) the... 

Cathode ray excited R emission Y2O3 By conversion to oxysulphide - Larach and Shrader (1973)... 

Most monitors are display terminals that use cathode-ray tube (CRT) displays, which function by exciting a layer of phosphors with an electron gun. These devices include monitors used with PCs and terminals used with mainframes or minicomputers. Features such as color, resolution, and size influence power requirements. Most PC monitors are... 

In a cathode ray tube, fast-moving electrons excite the gas, causing a giow between the eiectrodes. 

It is worth summarizing at this point the different excitation methods used for phosphors that will be referred to throughout this chapter. There are three types photoluminescence (PL) which is based on initial excitation by absorption of light, cathodoluminescence (CL) which is based on bombardment with a beam of electrons, as in a cathode ray tube (CRT) and electroluminescence (EL) which is based on application of an electric field (either a.c. or d.c.) across the phosphor. 

The results of their decay-time measurements are summarized in Table IX. The measurements were made using either cathode-ray or ultraviolet excitation. For the emissions excited by cathode rays the technique of Bril and Klasens (750) was employed. The ultraviolet excitation was accomplished with a cathode-ray tube equipped with a fast ultraviolet-emitting phosphor. 

Red-emitting Y202S Eu3+ phosphors were developed especially for excitation with cathode rays [5.345], [5.346]. Production generally starts from mixed rare-earth oxides, which are fired with sodium carbonate and sulfur. The polysulfide formed... 

Luminescence color is determined by visual comparison, by calculation of the color coordinates x and y from the emission spectrum, or by means of a tristimulus colorimeter under the excitation definitive for the application (UV radiation, cathode rays, etc.). 

Phosphors for cathode-ray tubes, television screens, monitor screens, radar screens, and oscilloscopes are tested under electron excitation. Electron energy and density should be similar to the conditions of the tube in which the screen will be used. The phosphors are sedimented or brushed onto light-permeable screens and coated with an evaporated aluminum coating to dissipate charge. The luminescence brightness and color of the emitted light are measured with optical instruments such as photomultipliers or spectrophotometers. 

Decay. The decay time requirements must be adhered to very precisely for cathode-ray tube phosphors. The measuring devices consist of fast excitation sources (flash lamps, lasers), photomultipliers with very low time constants, and an oscilloscope [5.440]. 

The luminescence process itself involves 11) absorption of energy (2) excitation, and tT) emission of energy, usually in the form of radiation in the visible portion of Ihe spectrum. The type of luminescence is usually defined by the excitation means, i.e.. irn/W luminesce nee where excitation is hy cathode rays, as in a television kinescope. The most commonly encountered types of luminescence arc listed in Table I. 

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