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Unidentified Luminescence Centers

In our study we found that H3, H4, S2 and S3 centers are characterized by relatively broad bands with A ax at 520-545 nm, sometimes accompanied by very weak zero-phonon lines at 489 and 523 nm (S2), 498 (S3) and 503 (H3) nm. It is very difficult to distinguish between the centers of this group, especially when they present together. Under pulse laser excitation the decay time differences enable more definite recognition. Different decay components in the green part of the spectrum allow us to establish the presence of H3 (12 ps) and S3 (126 and 213 ps) centers. These broad bands are sometimes accompanied by narrow lines of GR1 center at 794 nm and by system at 700 and 788 nm (Bokii et al. 1986 Davies 1994). The relatively broad fine at 463 nm with a decay time of 312 ps appears which is not described in the hterature (Fig. 4.72). [Pg.245]

This luminescence band is believed to be due to segregation of defects B1, which is a relatively large spheroid of aggregates of nitrogen and is characterized by strong N9 (236 and 230.8 nm) and weak NIO (240 and 248 nm) absorption systems. It gives white-blue luminescence (Fig. 4.71) excited by UV shorter that 240 nm with practically structureless broadband. Its luminescence decay is characterized by three components, mainly 25 ns, 100 ps and 3 ms. [Pg.245]

The luminescence spectrum of the Canada apatite contains the yellow band, which is similar to Mn + emission in the Ca(II) site (Fig. 5.71). Nevertheless, this band has short decay time, which is not suitable for strictly forbidden d-d transitions in Mn +. It dominates in the time-resolved spectrum with a delay of 10 ps and gate of 100 ps when the shorter-lived centers are quenched, while the longer-Hved ones are not detected. A change in the lifetime may be indicative of the energy transfer from Mn + by a radiationless mechanism. A condition necessary for this mechanism is coincidence or a close distance between energy level pairs of the ion sensitizer and the ion activator. Here, the process of luminescence is of an additive nature and a longer duration and greater quantum yield of the activator luminescence accompany a reduced [Pg.245]

Nevertheless, such interpretation contradicts with the fact, that after heating at 800 °C the short-hved yellow band disappeared and a usual long-hved Mn luminescence appears (Eig. 5.71d). Thus short-hved emission maybe not connected with the Mn center, but with another center, which transforms to Mn as result of oxidizing heating. To check this possibility time-resolved excitation spectrum of the yellow band with a short decay time was determined, because it is very characteristic for Mn +. It was found that the excitation spec- [Pg.246]

Certain similarity may be seen between this luminescence and short-Hved orange emission in calcite, which has been ascribed to radiation-induced center (Fig. 5.67). It is possible that natural irradiation may be a reason of orange luminescence in apatite also. [Pg.247]


Fig. 5.71. a-f Unidentified emission center in apatite laser-induced time-resolved luminescence spectra of apatite, a Steady-state luminescence spectrum b Time-resolved spectrmn with narrow gate where yellow band with short decay time dominates c-d Time-resolved spectra after heating at 800 °C e-f Excitation bands of Mn and short-lived yellow band, correspondingly... [Pg.246]

Fig. 5,72. a-f Unidentified emission centers in laser-induced time-resolved luminescence spectra of zircon... [Pg.247]

Besides confidently identified centers, the possible participation of Mn and is proposed. The centers, such as Mn ", Cr, Cr +, and V are described, which are not found in minerals yet, but are known in synthetic analogs of minerals, such as apatite, barite, zircon and corundum. Besides that, the centers Ni " and Ti " are discussed as possible participants in mineral luminescence. The last part of this chapter is devoted to unidentified emission lines and bands in apatite, barite, calcite and zircon. [Pg.362]


See other pages where Unidentified Luminescence Centers is mentioned: [Pg.245]    [Pg.245]    [Pg.247]    [Pg.249]    [Pg.252]    [Pg.245]    [Pg.245]    [Pg.247]    [Pg.249]    [Pg.252]    [Pg.74]   


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