Titanite absorption spectrum

The lines at 686 and 693 nm with a long decay time of approximately 1 ms in the titanite emission spectrum are not correlated with any other lines and bands (Fig. 4.34). Such lines are very typical for Cr in a high field coordination and may be connected with such a center. The broad luminescence band appears peaking at 765, which may be ascribed to Cr + in a weak field coordination. The band at 765 nm has distinct dips at 749, 762, 793, 798, 804 and 820 nm. Comparison with the titanite absorption spectrum (Fig. 5.19) demonstrates that those lines exactly coincide with the absorption spectrum of Nd (Bakhtin and Gorobets 1992). Cr is a good energy sensitizer, because it has broad, allowed absorption bands with a broad emission spectrum, which overlaps the absorption bands of the lasing ion (Nd " ", Ho " ). 

Titanite has rather unusual luminescence of Tm + (Gaft et al. 2003b). The lines near 800 nm are very characteristic for its luminescence spectra under different excitations (Fig. 4.34). It is interesting to note that the fines at 796,806 and 820 nm present also in optical absorption spectra of titanite (Fig. 5.21). Such absorption fines are usually ascribed to electron transitions to the fs/2 level of Nd " ". Thus in such cases it is logical to suppose that the emission fines at 800 nm have to be correlated with other Nd " luminescence, for example with IR emission from the " 3/2 level. Nevertheless, this is not the case. For example, with Aex = 488 nm excitation the fines at 800 nm are absent, while the IR emission of Nd " " is very strong. The same situation is present in the ionoluminescence spectrum, where the fines near 800 nm are absent and the luminescence of Nd " " presents (Yang 1995). Thus it is possible to suppose that the fines near 800 nm with a relatively short decay time of 60 ps belong to another luminescence center. 

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