부산대학교 도서관

Novel Nd3+/Yb3+co-doped sodium calcium silicate glasses were prepared by melting quenching method. Spectroscopic study was carried out as a function of doping content by fixing sensitizer (Nd3+) concentration to 0.2 mol% and adjusting activator (Yb3+) from 0 to 1.0 mol%. The energy transfer (ET) mechanisms between Nd3+and Yb3+are discussed based on their energy levels and excitation power-dependence emission intensity. Results show that the presence of Yb2+might be considered for the Nd3+-free and co-doped samples. The ET was confirmed by the down-conversion NIR emission spectra of the doped and co-doped samples under excitation at 808 nm. The mechanisms observed seem to involve only one VIS absorbed photon for each NIR emitted via direct energy transfer between 4F3/2of Nd2+and 2F5/2of Yb3+compensated by phonon assistance due to energy gap between these levels. The efficiency of ET increases with the ytterbium content up to almost 90% for the sample with 1 mol% of Yb2O3, which was evaluated by lifetime measurements. Up-conversion photoluminescence by exciting trivalent ions of neodymium (808 nm) and ytterbium (975 nm) is reported. The observed up-converted emission bands are related to the 4f-4f transitions of Nd3+and the spin-forbidden 5d-4f transition of Yb2+. Nd3+up-conversion emission is observed under 975 nm excitation, presenting an almost quadratic emission dependence with power excitation, which suggests that two laser photons participate in the up-conversion (UC) process, showing that ET occurs by a phonon-assisted energy transfer and cooperative energy transfer.