Physics and Chemistry of Minerals

, Volume 34, Issue 7, pp 437–444

Color centers in topaz: comparison between neutron and gamma irradiation

  • K. Krambrock
  • L. G. M. Ribeiro
  • M. V. B. Pinheiro
  • A. S. Leal
  • M. Â. de B. C. Menezes
  • J. -M. Spaeth
Original Paper

Abstract

Neutron- and gamma irradiation-induced paramagnetic centers in natural colorless topaz from four different Brazilian localities were studied by electron paramagnetic resonance (EPR) and optical absorption as a function of irradiation dose and thermal treatment. Gamma irradiation doses were applied up to 1,000 kGy with a dose rate of 15 kGy h−1. For the neutron irradiation experiments, a neutron flux of 4 × 1012 cm−2 s−1 was used with an integrated flux of up to 1 × 1018 cm−2. From the experiments, it is concluded that brownish colors are induced by gamma-rays and may be associated with a single broad isotropic EPR line with g = 2.015(2). Both the EPR line and the related optical absorption band at 460 nm (2.7 eV) are lost during thermal treatments between 150 and 200°C. Fast neutrons create the paramagnetic peroxyl radicals O2 and the paramagnetic O hole centers. The O centers have the same thermal stability as the optical absorption band at 620 nm (2.0 eV). It is confirmed that the absorption due to the O center is responsible for the blue color in topaz. Both color centers and their absorption bands are discussed in the context of O bound small polarons.

Keywords

Topaz Color Color enhancement Color centers EPR Irradiation Small polaron 

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Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  • K. Krambrock
    • 1
  • L. G. M. Ribeiro
    • 1
  • M. V. B. Pinheiro
    • 1
  • A. S. Leal
    • 2
  • M. Â. de B. C. Menezes
    • 2
  • J. -M. Spaeth
    • 3
  1. 1.Departamento de Física, ICExUniversidade Federal de Minas GeraisBelo HorizonteBrazil
  2. 2.Centro de Desenvolvimento da Tecnologia Nuclear (CDTN), Comissão Nacional de Energia Nuclear (CNEN)Serviço de Reator e Irradiações - TR3Belo HorizonteBrazil
  3. 3.Universität PaderbornPaderbornGermany

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