INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF PHYSICS: CONDENSED MATTER J. Phys.: Condens. Matter 15 (2003) 8235–8252 PII: S0953-8984(03)69718-3 Structure of dysprosium and holmium phosphate glasses by the method of isomorphic substitution in neutron diffraction Richard A Martin 1 , Philip S Salmon 1,4 , Henry E Fischer 2 and Gabriel J Cuello 3 1 Department of Physics, University of Bath, Bath BA2 7AY, UK 2 LURE, Centre Universitaire Paris-Sud, BP 34, F-91898, Orsay C´ edex, France 3 Institut Laue–Langevin, BP 156, F-38042, Grenoble C´ edex 9, France Received 28 September 2003 Published 25 November 2003 Online at stacks.iop.org/JPhysCM/15/8235 Abstract The relative distribution of rare-earth ions R 3+ (Dy 3+ or Ho 3+ ) in the phosphate glass RAl 0.30 P 3.05 O 9.62 was measured by employing the method of isomorphic substitution in neutron diffraction and, by taking the role of Al into explicit account, a self-consistent model of the glass structure was developed. The glass network is found to be made from corner sharing PO 4 tetrahedra in which there are, on average, 2.32(9) terminal oxygen atoms, O T , at 1.50(1) Å and 1.68(9) bridging oxygen atoms, O B , at 1.60(1) Å. The network modifying R 3+ ions bind to an average of 6.7(1) O T and are distributed such that 7.9(7) R– R nearest neighbours reside at 5.62(6) Å. The Al 3+ ion also has a network modifying role in which it helps to strengthen the glass through the formation of O T –Al–O T linkages. The connectivity of the R-centred coordination polyhedra in (M 2 O 3 ) x (P 2 O 5 ) 1−x glasses, where M 3+ denotes a network modifying cation (R 3+ or Al 3+ ), is quantified in terms of a parameter f s . Methods for reducing the clustering of rare-earth ions in these materials are then discussed, based on a reduction of f s via the replacement of R 3+ by Al 3+ at fixed total modifier content or via a change of x to increase the number of O T available per network modifying M 3+ cation. 1. Introduction The incorporation of rare-earth ions, R 3+ , into phosphate glasses confers these materials with many interesting opto-electronic and magneto-optical properties which give them application as, for example, lasers and Faraday rotators [1–7]. It is therefore desirable to understand the interactions between the rare-earth ions, and their mediation by the matrix material, in order 4 Author to whom any correspondence should be addressed. 0953-8984/03/498235+18$30.00 © 2003 IOP Publishing Ltd Printed in the UK 8235