Radio-colouration of diamond: a spectroscopic study

Autor(en)

Lutz Nasdala, Dieter Grambole, Manfred Wildner, Alexander M. Gigler, Thomas Hainschwang, A.M. Zaitsev, Jeff W. Harris, H Judith Milledge, Dan J: Schulze, Wolfgang Hofmeister, Walter A. Balmer

Abstrakt

We have undertaken a study of the common green or orange-brown spots at the surface of rough diamond specimens, which are caused by alpha particles emanating from radioactive sources outside the diamond. Richly coloured haloes represent elevated levels of structural damage, indicated by strong broadening of the main Raman band of diamond, intense strain birefringence, and up-doming of spots due to their extensive volume expansion. Green radio-colouration was analogously generated through the irradiation of diamond with 8.8 MeV helium ions. The generation of readily visible radio-colouration was observed after irradiating diamond with =1015 He ions per cm2. The accumulation of such a high number of alpha particles requires irradiation of the diamond from a radioactive source over long periods of time, presumably hundreds of millions of years in many cases. In the samples irradiated with He ions, amorphisation was observed in volume areas where the defect density exceeded 5 × 10-3 Å-3 (or 0.03 dpa; displacements per target atom). In contrast, graphitisation as a direct result of the ion irradiation was not observed. The green colouration transformed to brown at moderate annealing temperatures (here 450 °C). The colour transformation is associated with only partial recovery of the radiation damage. The colour change is mainly due to the destruction of the GR1 centre, explained by trapping of vacancies at A defects to form the H3 centre. An activation energy of ~2.4 ± 0.2 eV was determined for the GR1 reduction. The H3 centre, in turn, causes intense yellowish-green photoluminescence under ultraviolet illumination. Radio-colouration and associated H3 photoluminescence are due to point defects created by the ions irradiated, whereas lattice ionisation is of minor importance. This is concluded from the depth distribution of the colouration and the photoluminescence intensity (which corresponds to the defect density but not the ionisation distribution pattern). The effect of the implanted He ions themselves on the colour and photoluminescence seems to be negligible, as radio-colouration and H3 emission were analogously produced through irradiation of diamond with C ions. The photoluminescence emission becomes observable at extremely low defect densities on the order of 10-6 Å-3 (or 0.000006 dpa) and is suppressed at moderate defect densities of ~5 × 10-4 Å-3 (or ~0.003 dpa). Intensely brown-coloured diamond hence does not show the H3 emission anymore. Anneals up to 1,600 °C has reduced considerably irradiation damage and radio-colouration, but the structural reconstitution of the diamond (and its de-colouration) was still incomplete.

Organisation(en)

Institut für Mineralogie und Kristallographie

Externe Organisation(en)

Helmholtz-Zentrum Dresden-Rossendorf, Ludwig-Maximilians-Universität München, Gemlab Gemological Laboratory, City University of New York, University of Glasgow, University College London, University of Toronto, Johannes Gutenberg-Universität Mainz, Chulalongkorn University

Journal

Contributions to Mineralogy and Petrology

Band

165

Seiten

843-861

Anzahl der Seiten

19

ISSN

0010-7999

DOI

https://doi.org/10.1007/s00410-012-0838-1

Publikationsdatum

2013

Peer-reviewed

Ja

ÖFOS 2012

1030 Physik, Astronomie, 105116 Mineralogie

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/027b6288-1f04-46e1-80ef-81f724393a95