The solar cells efficiency may be improved by better exploitation of the solar spectrum, making use of the downconversion mechanism, where one high energy photon is cut into two low energy photons [1]. The choice of the matrix is a crucial point to obtain an efficient down-conversion process with rare-earth ions. When energy transfer between rare earth ions is used to activate this process, high emission and absorption cross sections as well as low cutoff phonon energy are mandatory. A low phonon energy host lattice reduces non-radiative transition rates leading to the increase of the luminescent quantum yield and of the energy transfer efficiency. Recently, some studies have demonstrated that fluoride and oxyfluoride glasses may be valid systems to support an effective quantum cutting process [2-4]. As a fluoride material, the relatively low phonon energy, around 600cm-1, of the ZLAG (70ZrF4 23.5LaF3 0.5AlF3 6GaF3 in mol%) glass makes it highly suitable for applications involving energy transfers. In this study, attention is focused on the assessment of the energy transfer efficiency between the Pr3+ and Yb3+ ions in bulk fluoride glasses ZLAG.