Calcite excitation spectra

Two types of Ce centers in calcite were detected by steady-state spectroscopy (Kasyanenko and Matveeva 1987). The first one has two bands at 340 and 370 nm and is connected with electron-hole pair Ce -COj". The second one has a maximum at 380 nm and was ascribed to a complex center with Ce and OH or H2O as charge compensators. Such a center becomes stronger after ionizing irradiation and disappears after thermal treatment. The typical example of Ce luminescence in the time-resolved liuninescence of calcite consists of a narrow band at 357 nm with very short decay time of 30 ns, which is very characteristic for Ce " (Fig. 4.13a). It was found that Ce " excitation bands occurs also in the Mn " " excitation spectrum, demonstrating that energy transfer from Ce to Mn " occurs (Blasse and Aguilar 1984). 

Fig, 5.66. Laser-induced time-resolved luminescence spectrum (a) and excitation spectrum (b) of radiation induced center in calcite... 

Under short-waved UV lamp excitation (254 nm) visually observed luminescence of calcite is violet-blue with very long phosphorescence time of several seconds. Under long-waved UV lamp excitation (365 nm) calcite exhibits visually the same violet-blue luminescence as under 254 nm excitation, but long phosphorescence is not detected. Under short laser excitations, such as 266 and 355 nm, at 300 K calcite demonstrates intensive UV-violet emission band peaking at 415 nm with half-width of 55 nm (Fig. 5.76a). Excitation spectrum of this band is composed of short waved tail in the spectral range less... 

Nevertheless, such interpretation cmitradicts the fact, that after heating at 800 °C the short-lived yeUow band disappeared and a usual long-lived Mn luminescence becomes visible (Fig. 5.111c, d). Time-resolved excitation spectrum of short lived yellow band consists of one main broad band with extremely low Stocks shift and is absolutely different from those for Mn + (Fig. 5.11 le-f). Certain similarity may be seen between this luminescence and short-lived orange emission in calcite, which has been ascribed to radiation-induced center. It is possible that natural irradiation may be a reason of orange luminescence in apatite also. 

Figure 4.19c demonstrates time-resolved luminescence spectra of calcite, Franklin, under 266 nm excitation. A very intensive UV band at 312 nm with short decay time of 120 ns is detected. It may not be connected with Ce emission, because its spectrum situated at longer wavelength near 400 nm (Fig. 4.19e). The excitatimi spectrum of the band at 312 nm consists of one band at 240 nm (Gaft et al. 2002a).

Fig. 6.26 (a-d) Short-lived orange luminescence spectrum (X x = 532 nm) of radiation-induced center in calcite and its decay as a function of delay time (a). Gated Raman spectra with excitation at 532 nm and gate widths of 10 ns (b) and 0.5 ns (d). CW Raman spectrum with excitation at 785 nm (c)... 

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