Topaz luminescence

Three slightly different octahedrally coordinated centers have been found in topaz by the EPR method (Schott et al. 2003), thus its participation in topaz luminescence is possible. 

Fig. 4.48. a-f Laser-induced time-resolved luminescence spectra of topaz demonstrating different Cr + and possibly Mn + centers... 

Connection of V with 833 and 847 nm lines with long decay time in luminescence spectrum of topaz (Fig. 5.29e,f) is also possible (Gaft et al. 2003a). 

Color centers in topaz can be produced by irradiation with fast neutrons and gamma-rays (Platonov et al. 1989). It was found that luminescence bands are connected with such color centers, which may be detected by steady state and time-resolved spectroscopy (Marques et al. 2000). The detected luminescence bands have been connected with both impurities and structural changes. 

Steady-state luminescence of topaz from Ouro Preto, Brazil has been studied in (Tarashchan 1978 Tarashchan et al. 2005 Taran et al. 2003). It was established that all photoluminescence characteristics of variously colored topazes are due to three structurally non-equivalent Cr " centers isomorphically substituting Al " in the topaz structure and forming [Cr04F2] , [Cr040H,Fn , and... 

Taran M, Tarashchan A, Rager H et al (2003) Optical spectroscopy study of variously colored gem-quality topazes from Ouro Preto, Minas Gerais, Brazil. Phys Chem Miner 30 546-555 Tarashchan A (1978) Luminescence of minerals. Naukova Dumka, Kiev (in Russian)... 

Tarashchan A, Taran M, Rager H, Iwanuch W (2005) Luminescence spectroscopic study of Cr in Brazilian topazes from Ouro Preto. Phys Chem Miner 32(10) 679-690 Tolstoy N, Shinfue L (1960) Kinetick of emission of chromium luminophores. Opt Spectrosc 9 415 19... 

Steady-state luminescence of topaz has been studied by Tarashchan (1978). At 77 K narrow lines at 680, 696, 712 and 730 nm have been ascribed to single (R-Unes) and Cr -paires (N-lines). We studied two transparent, four yeUow and one orange natural topaz. Two transparent precious stones have not been subjected to destructive chemical analyses. In other samples their Cr, Mn and V craicentra-ticms have been measured by ICP-AS method (Table 4.19). Absorption spectrum typical for Cr has been detected only in red topaz with highest Cr content of 500 ppm. Spectrum clearly revealed two broad bands typical of the octahedrally coordinated Cr (Gaft et al. 2003a). The bands centered at 418 and 533 nm evidently correspond to the spin-allowed " A2g T 2g and " Tig transitions,... 

Luminescence spectra at 300 K of all topaz samples contain strong narrow lines at approximately 680 and 684 nm and weaker line at 695 nm together with relatively broad band (half-width of 1100 cm ) peaking near 680 nm. In the purest form such luminescence was detected in precious transparent topaz (Ural) where other luminescence lines are not detected (Fig. 4.114a). The temporal behavior of the lines and the band in time-resolved spectra is somewhat different, where the band has shorter decay and dominates in the spectra with narrow gate starting from... 

The time-resolved spectra of topaz samples with elevated Cr contents, starting from 180 ppm, contain additional luminescence lines with different excitation and temporal behaviors. Luminescence spectra at 300 K of red topaz under = 266 mn... 

Luminescence of V has been found in a-Al203 under argon laser excitation at 514.5 nm, which consists of two narrow IR lines with the strongest one at 1026 nm, characterized by decay time of 1.6 ps at 77 K (Champagnon and Duval 1977). Connection of V " " with 833 and 847 nm lines with long decay time in luminescence spectrum of topaz (Fig. 5.53e, f) is also possible (Gaft et al. 2003a). 

Marques C, Santos L, Falcao A et al (2000) Luminescence studies in colour centers produced in natural topaz. J Lnmin 87-89 583-585... 

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