Abstract
Stochastic dynamics of individual co-doped Er:Yb upconversion nanoparticles (COEY NPs) were investigated from experiments and simulations. The COEY NPs were characterized by high-resolution scanning electron microscopy, dynamic light scattering, and zeta potential measurements. Single COEY NP measurements were performed by fluorescence upconversion micro-spectroscopy and optical trapping. The home-built apparatus was initially calibrated by performing individual trajectory measurements to determine diffusion coefficients in solution from displacement histograms, mean-squared displacement (MSD), and power spectra. MSDs from single COEY NP exhibited time-dependent diffusion coefficient which was compared with Brownian dynamics simulations of a viscoelastic model of harmonically bound spheres. Experimental time-dependent two-dimensional trajectories of individual COEY NP revealed correlated two-dimensional nanoparticle motion. The measurements were compared with stochastic trajectories calculated in the presence of a non-conservative rotational force field. Overall, the complex interplay of COEY NP adhesion, thermal fluctuations and optical forces led to a rich stochastic behavior of these nanoparticles.
© 2017 Optical Society of America
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