Chrysoberyl luminescence

Two types of Cr + luminescence centers have been found in steady-state natural alexandrite, characterized by J -lines at approximately 680 and 692 nm, accompanied by very many M-lines of Cr-Cr pairs (Tarashchan 1978). Those centers have been identified as connected with substitutions of AP" in different structural sites. It was found that natural alexandrites with very rare exceptions are characterized by very low CL intensities (Ponahlo 2000). Pulse CL study revealed that the spectrum consists of a relatively broad red band peaking at 685-695 nm, accompanied by narrow lines with the strongest one at 679 nm and the weaker ones at 650,655,664,700,707 and 716 nm. All lines and bands have been ascribed to several Cr + centers (Solomonov et al. 2002). The natural chrysoberyl and alexandrite in our study consisted of six samples. The laser-induced time-resolved technique enables us to detect two different Cr and possibly Mn + and V emission centers (Figs. 4.54-4.55). 

Fig. 4.54. Laser-induced steady-state luminescence spectra of alexandrite (a-c) and chrysoberyl (d) demonstrating different Cr and possibly V centers. Vertical polarisation - straight line, horizontal polarization - dash line...

Luminescence similar to those in zoisite has been found in the laser-induced time-resolved spectrum of chrysoberyl (Fig. 4.54d). A relatively broad band accompanied by narrow lines at 698,703 and 717 nm with a decay time of 150 ps, which are not connected with Cr emission, may be preUminary ascribed to V luminescence. 

The Cr " luminescence properties in natural chrysoberyl minerals have been studied as a function of the Cr content as well as impurities such as Fe and V. A competition was foxmd between Cr and V for very low Cr concentration with the vanishing of Cr " emission from Cr " ions located in inversion site. The Fe " ions substitute in mirror site efficiently with a strong impact on the Cr " lifetime of mirror site (Ollier et al. 2015). 

Figure 4.128 presents additional luminescence spectra detected in chrysoberyl. Their origin needs further investigation but most probably they are coimected to metal-oxygen complexes. 

Fig. 4.127 (a-b) Laser-induced time-resolved luminescence spectra of chrysoberyl demonstrating different Cr centers... 

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). 

---

See also in sourсe #XX -- [ ]

---