Research Signpost 37/661 (2), Fort P.O., Trivandrum-695 023, Kerala, India Photonic Glasses, 2006: 115-149 ISBN: 81-308-0063-2 Editor: Rolindes Balda 6 Optical properties of the rare earth ions in transparent oxyfluoride glass-ceramics Víctor Lavín, Fernando Lahoz, Inocencio R. Martín and Ulises R. Rodríguez-Mendoza Departamento de Física Fundamental y Experimental, Electrónica y Sistemas Universidad de La Laguna, E-38200 San Cristóbal de La Laguna Santa Cruz de Tenerife, Spain Abstract Highlights of the optical properties of transparent oxyfluoride glass-ceramics doped with Pr 3+ , Nd 3+ , Eu 3+ , Ho 3+ , Er 3+ , Tm 3+ and Yb 3+ ions are presented. A brief introduction on the interest of these materials is given in Section 1. In section 2 the general properties of the oxyfluoride glass-ceramics and the structure of the nanocrystals are emphasized. In section 3, the spectral intensities over the rare earth series are explained in the framework of the Judd-Ofelt theory analysing the changes of the values of the three Ω 2 , Ω 4 and Ω 6 intensity parameters in both the precursor Correspondence/Reprint request: Dr. Víctor Lavín, Departamento de Física Fundamental y Experimental, Electrónica y Sistemas. Universidad de La Laguna, E-38200 San Cristóbal de La Laguna, Santa Cruz de Tenerife, Spain. E-mail: vlavin@ull.es