Skip to content
Accessible Unlicensed Requires Authentication Published by De Gruyter June 30, 2020

Radiation-induced defects in montebrasite: An electron paramagnetic resonance study of O hole and Ti3+ electron centers

José R. Toledo ORCID logo, Raphaela de Oliveira ORCID logo, Lorena N. Dias, Mário L.C. Chaves, Joachim Karfunkel, Ricardo Scholz, Maurício V.B. Pinheiro and Klaus Krambrock ORCID logo
From the journal American Mineralogist

Abstract

Montebrasite is a lithium aluminum phosphate mineral with the chemical formula LiAlPO4(Fx,OH1–x) and considered a rare gemstone material when exhibiting good crystallinity. In general, montebrasite is colorless, sometimes pale yellow or pale blue. Many minerals that do not have colors contain hydroxyl ions in their crystal structures and can develop color centers after ionization or particle irradiation, examples of which are topaz, quartz, and tourmaline. The color centers in these minerals are often related to O hole centers, where the color is produced by bound small polarons inducing absorption bands in the near UV to the visible spectral range. In this work, colorless montebrasite specimens from Minas Gerais state, Brazil, were investigated by electron paramagnetic resonance (EPR) for radiation-induced defects and color centers. Although γ irradiation (up to a total dose of 1 MGy) did not visibly modify color, a 10 MeV electron irradiation (80 MGy) induced a pale greenish-blue color. Using EPR, O hole centers were identified in both γ- or electron-irradiated montebrasite samples showing superhyperfine interactions with two nearly equivalent 27Al nuclei. In addition, two different Ti3+ electron centers were also observed. From the γ irradiation dose dependency and thermal stability experiments, it is concluded that production of O hole centers is limited by simultaneous creation of Ti3+ electron centers located between two equivalent hydroxyl groups. In contrast, the concentration of O hole centers can be strongly increased by high-dose electron irradiation independent of the type of Ti3+ electron centers. From detailed analysis of the EPR angular rotation patterns, microscopic models for the O hole and Ti3+ electron centers are presented, as well as their role in the formation of color centers discussed and compared to other minerals.

  1. Funding

    The authors are grateful for financial support from the Brazilian agencies FAPEMIG, CNPq, CAPES, and FINEP.

References cited

Adrian, F.J., Jette, A.N., and Spaeth, J.M. (1985) Theory of indirect hyperfine interactions of oxygen-aluminum defects in ionic crystals. Physical Review B, 31, 3923–3931.Search in Google Scholar

Bershov, L.V., and Martirosyan, V.O. (1970) Electron and hole defects in nonirradiated single crystals of natural lithium and aluminum phosphates (ambligonite). Journal of Structural Chemistry, 10, 628–629.Search in Google Scholar

Clozel, B., Gaite, J.-M., and Muller, J.-P. (1995) Al-O–Al paramagnetic defects in kaolinite. Physics and Chemistry of Minerals, 22, 351–356.Search in Google Scholar

da Silva, D.N., Guedes, K.J., Pinheiro, M.V.B., Spaeth, J.M., and Krambrock, K. (2005) The microscopic structure of the oxygen–aluminium hole center in natural and neutron irradiated blue topaz. Physics and Chemistry of Minerals, 32, 436–441.Search in Google Scholar

Dias, L.N., Pinheiro, M.V.B., and Krambrock, K. (2009) Radiation-induced defects in euclase: Formation of O hole and Ti3+ electron centers. Physics and Chemistry of Minerals, 36, 519–525.Search in Google Scholar

Dias, L.N., Pinheiro, M.V.B., Moreira, R.L., Krambrock, K., Guedes, K.J., Filho, L.A.D.M., Karfunkel, J., Schnellrath, J., and Scholz, R. (2011) Spectroscopic characterization of transition metal impurities in natural montebrasite/amblygonite. American Mineralogist, 96, 42–52.Search in Google Scholar

Groat, L.A., Raudsepp, M., Hawthorne, F.C., Ercit, T.S., Sherriff, B.L., and Hartman, J. S. (1990) The amblygonite-montebrasite series: characterization by single- crystal structure refinement, infrared spectroscopy, and multinuclear MAS-NMR spectroscopy. American Mineralogist, 75, 992–1008.Search in Google Scholar

Groat, L.A., Chakoumakos, B.C., Brouwer, D.H., Hoffman, C.M., Fyfe, C.A., Morell, H., and Schultz, A. J. (2003) The amblygonite (LiAlPO4F)-montebrasite (LiAlPO4OH) solid solution: A combined powder and single-crystal neutron diffraction and solid-state 6Li MAS, CP MAS, and REDOR NMR study. American Mineralogist, 88, 195–210.Search in Google Scholar

Hill, F., and Lehmann, G. (1978) Atomic Hydrogen in the Mineral Brasilianite NaAl3(PO42(OH)4 Zeitschrift für Naturforschung—Section A Journal of Physical Sciences, 33, 1484–1486.Search in Google Scholar

Krambrock, K., Pinheiro, M.V.B., Guedes, K.J., Medeiros, S.M., Schweizer, S., and Spaeth, J.-M. (2004) Correlation of irradiation-induced yellow color with the O-hole center in tourmaline. Physics and Chemistry of Minerals, 31, 168–175.Search in Google Scholar

Krambrock, K., Ribeiro, L.G.M., Pinheiro, M.V.B., Leal, A.S., Menezes, M.Â. de B.C., and Spaeth, J.-M. (2007) Color centers in topaz: Comparison between neutron and gamma irradiation. Physics and Chemistry of Minerals, 34, 437–444.Search in Google Scholar

Li, R., Li, Z., and Pan, Y. (2012) Single-crystal EPR and DFT study of a VIAl–O–VIAl center in jeremejevite: Electronic structure and 27Al hyperfine constants. Physics and Chemistry of Minerals, 39, 491–501.Search in Google Scholar

Marfunin, A.S. (1979) Spectroscopy, Luminescence and Radiation Centers in Minerals. Springer.Search in Google Scholar

Mengeot, M., Bartram, R.H., and Gilliam, O.R. (1975) Paramagnetic holelike defect in irradiated calcium hydroxyapatite single crystals. Physical Review B, 11, 4110–4124.Search in Google Scholar

Meyer, B.K., Lohse, F., Spaeth, J.M., and Weil, J.A. (1984) Optically detected magnetic resonance of the (AlO40 centre in crystalline quartz. Journal of Physics C: Solid State Physics, 17, L31.Search in Google Scholar

Mombourquette, M.J., and Weil, J.A. (2006) EPR-NMR user’s manual. University of Saskatchewan, Saskatoon.Search in Google Scholar

Nassau, K. (2001) The Physics and Chemistry of Color: The Fifteen Causes of Color, 496 p. Wiley-VHC.Search in Google Scholar

Pake, and Estle (1973) The Physical Principles of Electron Paramagnetic Resonance. W.A. Benjamin.Search in Google Scholar

Requardt, A., Hill, F., and Lehmann, G. (1982) A firmly localized hole center in the mineral brazilianite NaAl3(PO42(OH)4 Zeitschrift für Naturforschung A, 37, 280–286.Search in Google Scholar

Schirmer, O.F. (2006) O-bound small polarons in oxide materials. Journal of Physics: Condensed Matter, 18, R667–R704.Search in Google Scholar

Schmitz, B., Jakubith, M., and Lehmann, G. (1979) A simple and convenient EPR standard for determination of g-factors and spin concentrations. Zeitschrift für Naturforschung A, 34, 906–908.Search in Google Scholar

Spaeth, J.-M., Niklas, J.R., and Bartram, R.H. (1992) Structural Analysis of Point Defects in Solids: An Introduction to Multiple Magnetic Resonance Spectroscopy. Springer-Verlag.Search in Google Scholar

Stoll, S., and Schweiger, A. (2006) EasySpin, a comprehensive software package for spectral simulation and analysis in EPR. Journal of Magnetic Resonance, 178, 42–55.Search in Google Scholar

Received: 2019-06-21
Accepted: 2020-01-26
Published Online: 2020-06-30
Published in Print: 2020-07-28

© 2020 Walter de Gruyter GmbH, Berlin/Boston