Influence of sol-gel matrices on the optical excitation of europium ions

Photoluminescence (PL), total photoluminescence excitation (TPLE), transmission and decay photo-luminescence experiments were done to establish the most efficient excitation mechanism of the euro-pium (Eu3+) ions in amorphous Al2O3 and Y3Al5O12 host matrices. Both matrices were fabricated using the sol-gel technique, doped with Eu3+ ions and sputtered on a flat quartz plate. Because of relatively low temperatures of annealing (200 °C), after this treatment the matrices should remain in an amorphous phase. In such a system, Eu3+ ions occupy the points having different site symmetries. However, based on characteristic features of the PL spectra, the effective site symmetry (ESS) parameter was defined to describe the PL properties of the Eu3+ ions in various matrices. Low intensive direct f-f transitions at 392, 465, 530 nm were observed in the TPLE spectra. The most intensive, wide excitation bands were centred at around 250–260 nm and the charge transfer process was found to be related to these excitation bands. Finally, a good correlation between photoluminescence lifetimes, the PL intensity and CT energy was observed