摘要
Novel Nd^(3+)/Yb^(3+)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(Nd^(3+))concentration to 0.2 mol%and adjusting activator(Yb^(3+))from 0 to 1.0 mol%.The energy transfer(ET)mechanisms between Nd^(3+)and Yb^(3+)are discussed based on their energy levels and excitation powerdependence emission intensity.Results show that the presence of Yb^(2+)might be considered for the Nd^(3+)-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^(4)F_(3/2)of Nd^(2+)and^(2)F_(5/2)of Yb^(3+)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 Nd^(3+)and the spin-forbidden 5d-4f transition of Yb^(2+).Nd^(3+)upconversion 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.
