Long decay 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. 

To preserve the reflection signal, a long decay phosphor is required. The phosphors used in the past were generally composed of two phosphors, one with a long decay. Thus, the screen exhibits two colors, that of the target and the other forming the background which is refreshed in every 360 ° rotation of the radar antenna. Radar phosphors include ... 

All of these were given in Table 6-2 of the last chapter. More recently, digital technology has replaced this type of CRT using long decay phosphors. A computer-controlled display utilizing a full color CRT has been developed for aircraft traffic control. Therein, the direction, size of target and altitude of aircraft are directly displayed upon the phosphor screen. 

This is the last subject we will examine. Long decay phosphors are used in phosphorescent paints as distinguished from radiolumlnescent paints. In the latter, radium ( is added to a suspension of a phosphor like... 

P-2 ZnS Cu ZnS, CuS, MgCl2, NaCl Green-emitting (520 nm) phosphor long decay for radar... 

Long decay time phosphor for use in radar. Orange emission at 575 nm... 

Y202S Eu " oxysulfide is a new kind of long-persistent phosphor. Figures 16.54 and 16.55 display the emission spectram of Y202S Eu and the afterglow decay... 

The most important mineral example is natural scheelite. ScheeUte emits a bright blue emission in a broad band centered at 425 nm (Fig. 4.9) with a decay time of several ps. Calcium tungstate CaW04 has long been known as a practical phosphor, and has been carefully studied. The intrinsic blue luminescence center is the complex ion in which the central W metal ion is... 

Most of the crystals studied gave exponential decays. One expects that the radiative lifetime of the europium 57)0 state should be something of the order of 10 msec. Bril and Wannaker find lifetimes as long as 2 msec for ultraviolet excitation and thus conclude that their phosphors apparently are not strongly affected by radiationless processes. 

The kinetics of the radioluminescence of organic compounds have not been widely published. Bollinger and Thomas (6) reported the room temperature decay kinetics of the long-lived scintillation component of trans-stilbene. The decay profile was non-exponential over the 100 fisec. time scale covered and, apart from intensity differences, the decay profile was identical for y-rays, neutrons and a-particles. However, the decay kinetics of several inorganic phosphors excited by low energy electrons—e.g., cathode ray tube phosphors—have been investigated (21). The theoretical treatment of the kinetics of the emission from... 

Serious candidates for application as a green phosphor in PTV tubes are YjSiOs Tb, Y3AIsO,2 Tb + and Y3(Al,Ga)50,2 Tb. The phosphor InB03 is excellent from several points of view, but its decay time is very long, viz. 7.5 ms... 

Willemite is used as a cathode-ray phosphor in terminal displays and oscilloscope tubes. The decay time is very long, viz. 25 ms [I]. This is mainly due to the spin- and parity- forbidden nature of the Ti -> Ai emission transition in the configuration of the Mn ion (Sect. 3.3.4.C), but there is also a contribution of afterglow. An even longer persislance is observed for samples to which As has been added. As a re.sult of the As addition, electron traps are formed ich trap the electrons for a certain time, so that the emission is delayed (Sect. 3.4). 

Eu Eu -" is the most well-known and widely applied example that shows a 5d 4/emission that can vary Irom long-wavelength ultraviolet to red. Its decay time is approximately 1 ps due to the fact that the emitting level contains (spin) octets and sextets, whereas the grormd-state level ( S from Af) is an octet. Thus, the spin-selection rule slows down the optional transition rate. Dependence of the host lattice on the emission color of the Eu " ion is determined by the same factors as in the case of the Ce ion. If the crystal field is weak and the amount of covalency low, the lowest component of the AfSd configuration lies below it. Similar to the above-mentioned Ce ", Eu ", a solely doped single-phased multicolor-emitting phosphor could obtained by cooperated in a compound with more than one cationic... 

Results of long-term tests (600 hours at 150°C) of PEMFCs with a PBI membrane doped with 85% phosphoric acid were reported in 2006 by Liu et al. In these tests, the membrane was not additionally humidified. Under these conditions the current density dropped from an initial value of 714 mA/cm to 300 mA/cm. After 130 hours, a gradual performance decay of 82 p.V/h began. This decay had accelerated to 270 tiV/h toward the end of the test. Apart from catalyst recrystallization, the voltage loss was attributed to an obvious gradual attack of the membrane assumed to be due to free radicals of the type OH and OOH, as well as to a gradual leaching of phosphoric acid from the membrane. 

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