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Modelling the concentration dependence of doping in optical materials

Contributed to the session in honour of Professor Patrick Jacobs. Modelling the concentration dependence of doping in optical materials. Robert A Jackson School of Physical and Geographical Sciences, Keele University, Keele, Staffs ST5 5BG, UK Mário E G Valerio

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Modelling the concentration dependence of doping in optical materials

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  1. Contributed to the session in honour of Professor Patrick Jacobs Modelling the concentration dependence of doping in optical materials Robert A Jackson School of Physical and Geographical Sciences, Keele University, Keele, Staffs ST5 5BG, UK Mário E G Valerio Department of Physics, Federal University of Sergipe, 49.100-000 São Cristóvão, Brazil

  2. Plan for talk • Introduction • Previous work – setting the scene • Methodology and results • Rare earth ions in YLiF4 • Thorium in LiCaAlF6, CaF2 • Future work • Patrick’s influence: research & conferences • General acknowledgements EURODIM2014: 14-18 July 2014 Canterbury, UK

  3. Introduction • Motivation – for optical materials, dopants are responsible for most of their important properties. • We can predict where they substitute in the lattice, and what form of charge compensation will be preferred. • We can predict morphologies for the perfect and doped materials. • A range of materials have been modelled in this way, including BaMgF4 and YLiF4. EURODIM2014: 14-18 July 2014 Canterbury, UK

  4. From EURODIM 2010 proceedings EURODIM2014: 14-18 July 2014 Canterbury, UK

  5. YLF Morphology T E Littleford, R A Jackson, M S D Read: ‘An atomistic simulation study of the effects of dopants on the morphology of YLiF4’, Phys. Stat. Sol. C10 (2), 156-159 (2013) (ICDIM 2012 paper) EURODIM2014: 14-18 July 2014 Canterbury, UK

  6. YLF morphology as affected by Ce dopants Surface energy approach Ce-YLF EURODIM2014: 14-18 July 2014 Canterbury, UK

  7. Relative effect on surfaces • The (011) surface becomes less prominent with the (111) surface disappearing. • The 021 surface is stabilised by Ce dopants and appears in the defective morphology.

  8. Predicting maximum dopant concentration – (i) • As well as knowing where and how the dopants are incorporated, how many are involved? • Consider doping YLiF4 (YLF) with M3+ dopants: (1-x) YF3 + x MF3+ LiF → Y1-xMxLiF4 • The procedure is to calculate the energy of this reaction (Esol) as a function of the dopant concentration x: Esol = E (Y1-xMxLiF4) - [(1-x) Elatt(YF3) + x Elatt(MF3) + Elatt(LiF)] EURODIM2014: 14-18 July 2014 Canterbury, UK

  9. Predicting maximum dopant concentration – (ii) • Calculating the first term (in red) has involved much thought! • The term is calculated using this expression: ED(x) = x EDML + Ep(1) • This splits the energy into defective and perfect terms (& assumes they don’t interact). • The final expression is then: Esol = E (x EDML+ Elatt(YLiF4)) - [(1-x) Elatt(YF3) + x Elatt(MF3) + Elatt(LiF)] EURODIM2014: 14-18 July 2014 Canterbury, UK

  10. Results for M3+ dopants in YLF* • Supercell methods can also be used to calculate the RHS term(and include all interactions). • Experimental data to test these results are needed! * T E Littleford, PhD thesis 2014 EURODIM2014: 14-18 July 2014 Canterbury, UK

  11. The nuclear clocks story • 229Th is being investigated for use in ‘nuclear clocks’; its first nuclear excited state is (unusually) only ~ 8 eV above the ground state, and can be probed by VUV radiation. • These promise up to 6 orders of magnitude improvement in precision over next generation atomic clocks, as well as enhanced stability. • Eric Hudson’s plenary lecture at EURODIM 2010 introduced the general field. EURODIM2014: 14-18 July 2014 Canterbury, UK

  12. Previous work Th4+ has to be doped into a suitable crystal; CaF2 and LiCaAlF6/LiSrAlF6are being investigated. Two previous papers (below, PDFs available) have modelled Th4+ in these materials, and established theenergetically favoured dopant sites and charge compensation mechanism (Ca2+ site with 2 F- interstitials). EURODIM2014: 14-18 July 2014 Canterbury, UK

  13. Solution schemes for Th4+ incorporation • LiCaAlF6 x ThF4 + (1-x) CaF2 + LiF + AlF3 LiThxCa1-xAlF6+2x • CaF2 x ThF4 + (1-x) CaF2  Ca1-xThxF2+2x (Assuming Th4+ substitutes at the Ca2+ site with compensation by 2 F-interstitials) EURODIM2014: 14-18 July 2014 Canterbury, UK

  14. How much Th4+can be doped into these materials? • Applying the method to LiCaAlF6 and CaF2 gives interesting contrasting results. • For LiCaAlF6 we calculate a maximum Th4+ concentration of ~ 5 mol %. Experimental values are eagerly anticipated! • For CaF2, we observe a linear relationship between solution energy and Th4+ concentration. Recent experimental concentrations are between 0.4-0.7 mol%, corresponding to solution energies in the range 2.3 – 3.5 eV. EURODIM2014: 14-18 July 2014 Canterbury, UK

  15. Conclusions & Future Work • The method we have developed gives results that agree with existing experimental data, but more is needed to test it and develop it further. • We would welcome collaboration with groups who have data on doping particular materials. EURODIM2014: 14-18 July 2014 Canterbury, UK

  16. A tribute to Patrick • I have much to be grateful to Patrick for. Early in my career he gave me this advice: • (Your research plan) must be realistic, but should bring out the fact that you have plenty of ideas and will be able to develop an active research programme which will involve not only yourself but future graduate students. • This was very useful to me as I began my career, and I have tried to continue to follow it ever since. EURODIM2014: 14-18 July 2014 Canterbury, UK

  17. Early research influence: Keele, August 1986 • In 1986 the development of photographic film was still a topic of commercial importance, and Patrick, Sean Corish, along with Roger Baetzold and Yen Tan from Kodak, visited Keele to try to improve the existing potentials for the silver halides. • My small part in this story was showing Patrick how to use CASCADE (based on HADES, and which preceded GULP). • This visit ultimately led to the following paper: EURODIM2014: 14-18 July 2014 Canterbury, UK

  18. Three body interactions in silver halides EURODIM2014: 14-18 July 2014 Canterbury, UK

  19. Meetings in Oxford and London, Ontario ‘Retirement’ meeting (London, Ontario, September 1989 EURODIM2014: 14-18 July 2014 Canterbury, UK

  20. ICDIM 1992 (Nordkirchen) EURODIM2014: 14-18 July 2014 Canterbury, UK

  21. EURODIM 1998 (Keele)(The last EURODIM/ICDIM conference attended by Patrick) EURODIM2014: 14-18 July 2014 Canterbury, UK

  22. Some more photos … 1981 1988  1998 1999  EURODIM2014: 14-18 July 2014 Canterbury, UK

  23. Final conclusions • Patrick’s influence on the EURODIM-ICDIM series of conferences has been considerable. • More generally, his influence on the field of solid state chemistry was significantand wide ranging, as is shown by the diversity of topics presented in this session. • He was always generous in his encouragement and enthusiasm, which is much appreciated by those who knew him. EURODIM2014: 14-18 July 2014 Canterbury, UK

  24. Acknowledgements Tom Littleford (Keele, UK) Jomar Amaral (UFS, Brazil) Thorsten Schumm (TU-Wien, Austria) Eric Hudson (UCLA, USA) EURODIM2014: 14-18 July 2014 Canterbury, UK

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