Uranyl emission spectrum

One of the most successful techniques of detecting small amounts (say 10-9 to 10 6g) of uranium is the fluorescence after incorporation in molten sodium fluoride22,181). Since the light emitted is green, and since the emission spectrum shows some vibrational structure, it was the general opinion before 1956 that some kind of imbedded uranyl... 

The emission spectra for uranyl-exchanged zeolites Y, mordenite and X all have differences but do show some fine structure and therefore resemble the solid state spectrum of uranyl acetate dihydrate. In fact, the spectrum of uranyl ions exchanged into sodium mordenite is very similar to that of the uranyl acetate dihydrate solid spectrum shown in Figure 1. Further support for our belief that some zeolites have a solution like environment and others have a solid like environment comes from the correlation between the crystallinity of these uranyl-exchanged zeolites and the appearance of some fine structure in the emission spectrum. We find no apparent correlation between this fine structure and the concentration of the uranyl ion in the zeolites even with a ten-fold change in the concentration of the uranyl ion. 

A characteristic example of case (b) is the uranyl ion (UO ). The Tie = 0— rig = 2 line dominates in the spectrum (Fig. 4b). The tungstate ion (WC)4 ) is a good example of case (c). The very broad emission spectrum (see Fig. 4c) does not show any vibrational structure at all, the Stokes shift is very large (—16,000 cm" ) and the zero-vibrational transition is not observable, not even at the lowest possible temperatures nor for the highest possible resolving powers. 

Figure 25. Laser-excited luminescence in fossil fish teeth from phosphorite beds in the Senonian Mishash formation, Israel. (A) Uranyl emission at 77 K indicating uranyl aqueous complexes. (B) after annealing at 1000 K the uranyl complexes are dehydrated . (C) Same as in A but spectrum collected at 300 K. From these data it was concluded that the uranyl resides in organic material and not in the apatite structure. Modified after Gaft et al. (1996b).

The resulting fluorescence emission spectrum obtained for the uranyl ion is shown in Figure 9.1. Note that UOa begins to emit fluorescence at 450 nm, and that the most intense bands fall in the green region of the visible spectrum. 

Figure 9.1. Spectra of uranyl nitrate. A The corrected emission spectrum of 10 M uranyl nitrate in 0.1 N ff2

Figure 5. Triboluminescence Spectrum of Uranyl Nitrate Hexa-hydrate. The photoluminescence excitation spectrum is shown for comparison the photoluminescence emission has been...

Emission Spectra. The emission spectra of the uranyl acetate dihydrate in solution and in the solid state are shown in Figure 1. The fine structure in the solid state spectrum is not observed in solution. The corresponding emission spectra of uranyl-exchanged zeolites. A, Y, mordenite and ZSM-5 are shown in Figures 2-4. Excitation is carried out at 366 nm. The emission spectra have been scanned in all cases between 450 nm and at least 630 nm. 

Emission due to excited state energy transfer has been reported in layered low dimensional rare earth complexes such as uranyl phosphates [50],cryptates [51] and platinum tetracyanides [52, 53]. The luminescence properties of the low dimensional rare earth compounds of the type RE[M(CN)2]3 where RE = Eu, Dy, Gd " and M = Au, Ag are also interesting in this regard. We recently reported [16] that efficient excited state energy transfer from the Au(CN)2 and Ag(CN)j ions to Eu " enhances the luminescence observed from the rare earth ion. A similar result is obtained from other rare earth salts [17]. In some cases vibronic structure appears in the luminescence spectrum. 

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