Scanning Microscopy


The thermoluminescence (TL) of synthetic zircons into which some impurities have been individually insert-ed is investigated. The results obtained show that, after X-irradiation at 77K, the synthetic zircons present three kinds of thermoluminescent emissions. The first is related to the OH- ions, the second is typical of the SiO44-groups, and the third is characteristic of RE3+ ions with RE = Dy, Tb, Gd, Eu, or Sm (RE = rare earth).

The OH- emission is a large band at 285 nm which appears at 115 and 160K.

The SiO44- TL emission consists of a 365 nm band observed at 100, 165, 205, 260, and 325K. The mechanisms associated with these TL peaks are fairly well described in terms of an electron trapped in the field of two positive charges, one substituted to silicon ion, the other to a neighbouring oxygen ion.

For temperatures up to 350K, the characteristic emissions of RE3+ are the consequence of an energy transfer mechanism from the TL emission as a result of recombination in SiO44- host groups or OH- centres to the RE3+ emitting activators. At temperatures higher than 350K, there are also some other RE3+ characteristic peaks which are interpreted in terms of charge transfer mechanisms.

The systematic compilation of results obtained with a series of natural zircons from various origins shows that the main TL properties are explained by the mechanisms described above.

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