Sol-gel glassy films of the SiO2-TiO2-PO2.5-ErO2.5 system containing nanocrystallites of ErPO4, were obtained through suitable heat treatments. Variations in the shape and intensity of the Er3+ photoluminescent signal around 1500 nm were linked to the nature of the host environment of the active ions; the specific features of the photoluminescent emission spectrum of the erbium 4I13/2 metastable level were interpreted in terms of structural changes in the glassy films. The photoluminescent spectrum was found to be sensitive to the order (crystalline) or disorder (amorphous) of the Er3+ ions neighbour within the glassy matrix. An amorphous environment led to a broadening of Er3+ PL emission band while a crystalline one was responsible for a drastic photoluminescent bandwidth narrowing. The presence of nanoscale heterogeneities caused a drastic photoluminescence intensity decrease. Changes in the shape of the decay curve of fluorescence lifetime were found also structurally dependent on volumetric defects, occurrence of phase separation and Er3+-Er3+ clustering effects as well. Variations in the shape and intensity of the Er3 + photoluminescent signal around 1500 nm were linked to the nature of the host environment of the active ions; the specific features of the photoluminescent emission spectrum of the erbium 4I13 / 2 metastable level were interpreted in terms of structural changes in the glassy films. The photoluminescent spectrum was found to be sensitive to the order (crystalline ) or disorder (amorphous) of the Er3 + ions neighbor within the glassy matrix. An amorphous environment led to a broadening of Er3 + PL emission band while a crystalline one was one for a drastic photoluminescent bandwidth narrowing. The presence of nanoscale heterogeneities caused a drastic photoluminescence intensity decrease. Changes in the shape of the decay curve of fluorescence lifetime were also structurally dependent on on volumetric defects, occurrence of phase separation and Er3 + -Er3 + clustering effects as well.