By A. H. Kitai (auth.), A. H. Kitai (eds.)
Historically, black physique radiation within the tungsten filament lamp was once our basic commercial capacity for generating 'artificial' mild, because it changed gasoline lamps. reliable country luminescent units for functions starting from lamps to monitors have proliferated because then, relatively because of the advance ment of semiconductors and phosphors. Our lights items are actually quite often phosphor established and this 'cold mild' is exchanging an expanding fraction of tungsten filament lamps. Even gentle emitting diodes now chal lenge such lamps for automobile brake lighting fixtures. within the region of knowledge monitors, cathode ray tube phosphors have proved themselves to be outstandingly effective mild emitters with very good color strength. the present push for flat panel screens is kind of excessive, and lots more and plenty confusion exists as to the place improvement and commercialization will ensue so much speedily, yet with the necessity for color, it really is now obvious that reliable kingdom luminescence will play a main position, as gasoline part plasma screens don't very easily let color on the excessive solution wanted at the present time. the long run problem to boost electroluminescent screens maintains, and excessive functionality fluorescent lamps at present remove darkness from liquid crystal monochrome and color screens. the advance of tri part infrequent earth phosphors is of specific importance.
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Extra resources for Solid State Luminescence: Theory, materials and devices
Sample text
If, however, heavy water is used (D 20, Vmax ~ 2200 cm -1) the efficiencies go up again. For solids these effects can be studied in NaLa(S04h· H 20 where the rare earth site is coordinated to one H 20 molecule only. The q values are 100% for Gd3+, 70% for Tb3+, 10% for Eu3+ and 1% for Sm3+ and Dy3+ [7,8]. In many compounds of Eu3+, Gd3+ and Tb3+ energy migration has been observed [6-8]. An example was given above for Gd3+. The Gd3+ ion transfers efficiently to Eu3+ and Tb3+, and Tb 3+ to Eu3+ which has the lowest emitting level of the three.
A characteristic example of case 2 is the uranyl ion (UO~ +). The m = 0--+ n = 2 line dominates in the spectrum (Fig. 4(b)). The tungstate ion (WOi -) is a good example of case 3. The very broad emission spectrum (see Fig. , 16 000 cm -1) and the zero-vibrational transition is not observable, not even at the lowest possible temperatures, or for the highest possible resolving powers. Fig. 4 (a) An example of an emission spectrum in the weak-coupling case. The spectrum consists of a line which corresponds to the zero-phonon transition.
It can be shown that the relative intensity of the zero-vibrational transition (n=O~m=O) is exp( -S) [5]. We can now divide our luminescent centres into three classes: 1. e. S < 1), so that the zero-vibrational transi- tion dominates the spectrum; 2. e. 1 < S < 5), so that the zero-vibrational transition is observable, but not the strongest line in the absorption or emission band; 3. e. S> 5), so that the zero-vibrational transition is so weak that it is not observable in the spectra. 4 shows three emission spectra that are representative of the three cases.