Continuous wave near-infrared phonon-assisted upconversion in single Nd3+-doped yttria nanoparticles

We report on Nd3+-doped yttrium oxide polycrystalline nanoparticles synthesis, their basic structural characterization and the observation of phonon-assisted upconversion in single nanoparticles with different Nd3+ doping levels. For upconversion studies, a frequency-locked CW Ti: Sapphire laser operating @ 820 nm, resonant with a Stark level of the Nd3+ ions F-4(5/2) manifold, was used to excite single nanoparticles on a home-made confocal microscope. To the best of our knowledge, luminescence ranging from 630 to 760 nm was observed for the first time from single Nd3+-doped yttria nanoparticles under such excitation conditions. Upconversion studies on different single nanoparticles revealed a good doping homogeneity and the upconversion emissions were found to be one-photon phonon-assisted processes.