Beryl luminescence

Vanadium complex luminescence may be supposed in chrysoberyl where artificial chrysoberyl activated by V exhibits read broad band luminescence with decay time of approximately 5 ps under UV excitation (Fig. 5.98). Similarly, pyromorphite usually has orange to yeUow UV excited luminescence characterized by broadband peaking at 580 nm (Fig. 4.60). It was earlier supposed that such luminescence is connected with (V04) emission center (Gaft 1984), but the possible role of Ag also may be considered (Gorobets and Rogojine 2001). Beside, blue emission band in beryl luminescence spectrum with short decay time of 1 ps (Fig. 4.122a) can also be connected with (V04) complex, especially because the similar emission has been found in radioluminescence spectrum of beryl with elevated ccmcentration of vanadium (Chithambo et al. 1995). 

Fig.4, 52. a-d Laser-induced time-resolved luminescence spectra of beryl demonstrating different Cr ", Fe " and possibly V and VO4 centers... 

Emerald, Cr " doped beryl, has a beryl structure with the Cr " impurity ions in highly distorted octahedron sites. The discovery of lasing action in emerald stimulated investigation of its luminescence properties. It was established that its tuning range is approximately 730-810 nm, while luminescence consists of a narrow line at 684 nm and a band peaking at 715 nm with similar decay times of 62 ps. The relative intensities of those line and band are different in a- and 7T-polarized spectra (Fabeni et al. 1991). 

The radio-luminescence of transition metal doped natural beryl has been studied (Chithambo et al. 1995). It was found that Mn containing samples gave intense red radio-luminescence with sharp emission lines, while the Mn activated beryl (morganite) emission is more than twice as bright as that from emerald. Such luminescence has been ascribed to Mn ", but it may be supposed that such emission is connected with Mn luminescence. The laser-induced time-resolved luminescence spectra of natural morganite revealed a band peaking at 730 nm, which may be preliminary ascribed to the Mn center (Fig. 4.52). 

The broad band peaking at 730 nm accompanied by a narrow doublet at 692 and 694 nm (Fig. 4.52) with a mutual decay time of 100 ps in the laser-induced time-resolved luminescence spectrum of beryl is not similar to the Cr emission in emerald. Thus we suppose that such typical emission may be connected with the center. 

In the time-resolved luminescence, Fe dominates spectra with long delay times. The examples may be seen in feldspars and obsidian (Fig. 4.43), woUastonite (Fig. 4.42b), zircon (Fig. 4.39d), and beryl (Fig. 4.52b). 

The luminescence properties in natural beryl minerals have been studied as a function of the Cr content as well as impurities such as Fe and V. It appears that the Cr crystal field is linked to the Cr amount and decreases when Cr increases. A competition between Cr and V was noticed for very low Cr concentration (Ollier et al. 2015). 

Fig. 4.124 (a-d) Laser-induced cw luminescence spectra of beryls under 532 nm laser excitation (http //rruff.info)... 

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