Color centers in topaz: comparison between neutron and gamma irradiation |
| |
| Authors: | K Krambrock L G M Ribeiro M V B Pinheiro A S Leal M Â de B C Menezes J -M Spaeth |
| |
| Institution: | 1.Departamento de Física, ICEx,Universidade Federal de Minas Gerais,Belo Horizonte,Brazil;2.Centro de Desenvolvimento da Tecnologia Nuclear (CDTN), Comiss?o Nacional de Energia Nuclear (CNEN),Servi?o de Reator e Irradia??es - TR3,Belo Horizonte,Brazil;3.Universit?t Paderborn,Paderborn,Germany |
| |
| 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 |
| 本文献已被 SpringerLink 等数据库收录！ |
|
