Data are presented on the induced optical absorption and EPR in Ba(PO 3 ) 2 -MgF 2 glasses activated with Tb 2 O 3 and Eu 2 O 3 . The effect of activator concentration on the EPR spectra of the ê and ê centers in glasses differing in fluoride content is analyzed. The results indicate that fluorophosphate glasses can be characterized by two capture volumes which may differ several times, depending on the activator concentration. At low activator concentrations, corresponding to the largest capture volume, the activator ions seem to be in a phosphate environment. The maximum Tb 3+ concentration is comparable to the Eu 3+ concentration at which the luminescence spectrum points to a phosphate environment of the rare-earth ion. O 4 2-O 3 2-

Spectroscopic properties of Eu3+ in the fluorophosphate glases are described. It is well known that fluorophosphate glasses are of special interest due to their potential as a laser host matrix and optical fiber amplifiers. Characteristic properties of these glasses are a low refractive index and a low dispersion. The high efficiency of cooperative fluorescence is believed to be one of the basic characteristics to elaborate optical fiber amplifiers. This process relies on a Colombian interaction between ions and is strong dependent on inter-ionic distances. In order to reduce the size of optical fiber amplifiers or to make compact waveguide amplifiers lasers, it is of importance to increase the active ion concentration. Preferable occupying, a certain regions in glass structure by ions-activators (so-called clustering)1 might help to solve the problem of low efficiency of cooperative fluorescence by achievement of high local concentrations of ions. The present study is focused on investigation of spectroscopic properties of Eu3+. Simple energy levels and the excitation from 7 F0 to 5D0 levels of an Eu3+ and fluorescence wavelengths being within visible range enable available interpretation of Eu3+ ion environment in glass structure. When the glass is irradiated with ultra violet light of 395 nm. it has an orange-red fluorescence. By using the irradiation, the 5 L6 level is populated. All the transitions are observed in the fluorescence spectrum from the 5 D0 level, which is populated by radiationless deactivation of the 5 L6 level.Fluorophosphate glasses doped with 1 mol% Eu 3+ have been prepared. Glass composition have been changed by replacement of fluoride component (usovite) by Ba(PO3)2. These compounds are more stable to moisture than other metaphosphates. Glass compositions are shown in Table 1. 2

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