Optical trapping and orientation-resolved spectroscopy of europium-doped nanorods

Europium-doped NaYF4 nanorods with a high aspect ratio are optically trapped using a single fibre tip optical tweezers. Three distinct trapping positions of the nanorods are observed: in contact with the fibre tip, close to the tip and 5 μm from the tip end. The direction and polarisation-dependent Eu3+ photoluminescence is investigated by recording the emission parallel and perpendicular to the nanorod long axis through the trapping fibre and the microscope objective, respectively. These spectroscopic measurements permit an unambigous determination of the nanorod orientation.