Down-and up-conversion processes in Nd^(3+)/Yb^(3+)co-doped sodium calcium silicate glasses with concomitant Yb^(2+)assessment

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.

Unveiling bulk and surface radiation forces in a dielectric liquid

Precise control over light-matter interactions is critical for many optical manipulation and material characterization methodologies,further playing a paramount role in a host of nanotechnology applications.Nonetheless,the fundamental aspects of interactions between electromagnetic fields and matter have yet to be established unequivocally in terms of an electromagnetic momentum density.Here,we use tightly focused pulsed laser beams to detect bulk and boundary optical forces in a dielectric fluid.From the optical convoluted signal,we decouple thermal and nonlinear optical effects from the radiation forces using a theoretical interpretation based on the Microscopic Ampère force density.It is shown,for the first time,that the time-dependent pressure distribution within the fluid chiefly originates from the electrostriction effects.Our results shed light on the contribution of optical forces to the surface displacements observed at the dielectric air-water interfaces,thus shedding light on the long-standing controversy surrounding the basic definition of electromagnetic momentum density in matter.