Alexandrite effect

The optical spectra of other colour-changing materials exhibiting the alexandrite effect , including chromium- and vanadium-bearing garnets and... 

Cations of the lanthanide elements also produce colours in some minerals through intra-electronic transitions within 4/orbitals (Adams, 1965 Bernstein, 1982). Absorption bands are usually sharp and weak, leading to pastel shades. Examples of such coloured minerals are monazite, bastnaesite, rhabdophane, xenotime, gadolinite, and certain apatites, calcites, scheelites and fluorites. As noted earlier, some rare earth-bearing minerals, notably fluorite and monazite, also display the alexandrite effect (Berstein, 1982 Schmetzer et al., 1980). 

Bernstein, L. W. (1982) Monazite from North Carolina having the alexandrite effect. Amer. Mineral., 67, 356-9. 

Schmetzer, K., Bank, H. GUbelin, E. (1980) The alexandrite effect in minerals chrysoberyl, garnet, corundum and fluorite. Neues Jahrb. Miner. Abh., 138,147-64. 

With an optical gap of about 9.9 eV, pure alumina is transparent in the visible and colorless domain. Like the electrical properties, the colored effects depend primarily on the impurities. Sapphire and raby have been the subject of numerous studies [BUR 84] and it is esthetically and scientifically interesting to mention the alexandrite effect (from the name of a chrysobeiyl (Al2Be04) containing a little Cr +) which is green in daylight and red if illnminated by an incandescent lamp [NAS 83]. 

Because chemical and structural properties of natural and artificial gems are very similar in this case, the possibilities of Raman and LIBS methods are rather limited. It was found that another laser-based techniques could be very effective for rapid spectroscopic discrimination between natural and synthetic emeralds, rubies, and alexandrite (Armstrong et al. 2000a,b). The first one is DRIFTS (Diffuse Reflectance Fourier Transformed Infra-Red Spectroscopy)... 

Comparing the QS laser with the long-pulsed 532-nm Nd YAG laser in the treatment of melasma, the latter produced less PIH because it lacks the photomechanical effects of the QS laser [126]. QS alexandrite laser or PLDL combined with 15-25% TCA peel and/or Jessner s solution was shown to be effective, safe, and relatively inexpensive treatment modalities in the recalcitrant pigmentary disorders [92]. Combination of QS alexandrite and ultrapulse CO lasers yielded statistically significant result in improving refractory melasma compared to QS alexandrite laser alone [5]. Erbium YAG used on patients with skin phototypes II-V may have demonstrated improvement but transient PIH developed 3-6 weeks after laser treatment [100]. 

Nanni CA, Alster TS (1999) Laser-assisted hair removal side effects of Q-switched Nd Yag, long-pulsed ruby, and alexandrite lasers. J Am Acad Dermatol 41(2 ptl) 165-171... 

Aldraibi MS, Touma DJ, Khachemoune A (2007) Hair removal with the 3-mec alexandrite laser in patients with skin types IV-VI efficacy, safety, and the role of topical steroids in preventing side effects. J Drugs Dermatol 6(l) 60-66... 

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