Barite laser-induced luminescence

We studied laser-induced time-resolved lirminescence of synthetic BaS04 artificially activated by Sn and foimd several intensive UV and blue bands evidently connected with Sn emission (Fig. 5.55). Similar bands have been also found in natural barite laser-induced luminescence spectra and we think that their connection with an Sn center is quite possible. 

Fig. 5.16. Laser-induced luminescence of barite 1 - after heating at 600 °C while violet luminescence of evidently Eu " appears 2 - after X-ray irradiation of the heated sample where blue shoulder appears, supposedly connected with Eu+ (Gaft and Rudenkova 1993)...

Figure 4.29 represents a typical laser-induced luminescence spectra recorded from natural barite with orange luminescence. At room temperature imder 308, 337 and 355 nm excitations orange luminescence consists of a very broad band peaking at 635 nm with a half-width of approximately = 150 nm (Fig. 4.29a). At lower temperatures up to liquid hehum the spectriun is very similar and only the half-width of A = 130 nm becomes a httle narrower (Fig. 4.29b). At all temperatures the spectra are not dependent on delay times and gate widths. The possible conclusion is that only one liuninescence center is responsible for this orange band. The decay time of luminescence is approximately 225 ps at 300 K and 275 ps at 4.2 K.

The spectra of the green laser-induced luminescence represented in Fig. 4.4a, together with their decay time, also allows its association with These luminescence spectra strongly differ from the spectral parameters of all known uranyl minerals. For this reason it is not possible to connect this type of green luminescence with finely dissipated uranyl phases. On the other hand, this luminescence is very similar in such different host minerals as sedimentary apatites, opalites, chalcedony, chert, quartz and barites. Luminescence independence from the minerals structure evidences that it may be connected with uranyl adsorption on the minerals surface, supposedly in the form of (UO2 X nH20)2+. 

Gaft M, Rudenkova I (1993) Laser-induced luminescence of barite after thmnal treatment. J Therm Anal 42 187-195... 

The natural barite in our study consisted of twenty-five samples of different origin. Concentrations of potential luminescence impurities in several samples are presented in Table 4.11. For the correct interpretation of the luminescent bands, artificial barite standards have been investigated, as nominally pure, and activated. The laser-induced time-resolved technique enables us to detect Ag+, Bi +, Bi, Eu, Ce +, Nd +, (U02) and several still not identified emission centers (Figs. 4.29-4.31). 

Fig. 4.29. a-c Laser-induced time-resolved luminescence spectra of barite with Ag" centers... 

Fig. 4.30. a,b Laser-induced time-re-solved luminescence spectra of barite with Bi " and Bi " ... 

The structure of celestine is similar to that of barites, with Sr taking the place of Ba. Steady-state luminescence of celestine is characterized by broad bands, which are associated with adsorption of water-organic complexes (Tarashchan 1978). The natural celestine in our study consisted of five samples. Laser-induced time-... 

---