Emission spectroscopy of NaYF4:Eu nanorods optically trapped by Fresnel lens fibers

NaYF4:Eu nanorods with high aspect ratios are elaborated and optically trapped using dual fiber optical tweezers in a counterpropagating geometry. High trapping efficiency is observed using converging beams, emitted from diffractive Fresnel lenses directly 3D printed onto cleaved fiber facets. Stable nanorod trapping and alignment are reported for a fiber-to-fiber distance of 200 mu m and light powers down to 10 mW. Trapping of nanorod clusters containing one to three nanorods and the coupling of nanorod motion in both axial and transverse directions are considered and discussed. The europium emission is studied by polarization-resolved spectroscopy with particular emphasis on the magnetic and electric dipole transitions. The respective sigma and pi orientations of the different emission lines are determined. The angles with respect to the nanorod axes of the corresponding magnetic and electric dipoles are calculated. Mono-exponential emission decay with decay time of 4-5 ms is reported. It is shown that the nanorod orientation can be determined by purely spectroscopic means. (C) 2022 Chinese Laser Press

Automated summary

In this study, NaYF4:Eu nanorods with high aspect ratios were successfully manipulated and optically trapped using dual fiber optical tweezers, with a focus on trapping efficiency, alignment, cluster trapping, motion coupling, and emission characteristics. The europium emission was studied through polarization-resolved spectroscopy, determining the orientation of different emission lines with respect to the nanorod axes. The findings suggest that nanorod orientation can be determined by spectroscopic means.