Diamond luminescence sorting

Diamond luminescence was studied mainly with the two following aims to carry out a fundamental investigation of its physical properties and to determine the optimal conditions for luminescent sorting of diamond bearing rocks. For the first task, diamond photoluminescence was studied at liquid nitrogen temperature at which luminescence centers are marked by characteristic zero-phonon fines and are much more informative then at room temperature. For the second task, were diamond is one of the first minerals for which luminescence sorting was used, liuninescence properties should be studied at 300 K. In the first stages it was established that X-ray luminescence of the A-band... 

Kimberliteisthe principal diamond bearing ore. In atypical mine such as the Premier Mine near Pretoria, South Africa, one hundred tons of kimberlite produce an average of thirty-two carats of diamond (6.4 g). Dieimonds are sorted from the mineral by an x-ray beam the diamond luminesces with the x-ray and the luminescence activates an air Jet which propels the diamond into a separate bin (Fig. 12.1).i ] Gemstones (a very small percentage) are then separated from the industrial-quality material. 

At the present time new deposits have been discovered which contain diamonds without luminescence under X-ray excitation. Sometimes the portion, which is unrecoverable in X-ray luminescent sorters, is big enough to warrant the development of a new sorting method. The luminescence spectra were investigated under excimer (193,222,248 and 308 nm), nitrogen (337 nm) and dye laser (340-360 nm) excitations (Fig. 8.2). 

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