We report stable and reproducible optical trapping of Eu-doped NaYF4 anisotropic nanorods using single fiber tip optical tweezers for investigating the orientation resolved emission spectra. The nanorods were elaborated by the hydrothermal process followed by annealing and centrifugation steps, resulting in a well-defined size distribution. Nanorod trapping was observed at two positions, first, in fiber tip contact and second, at a finite distance of 4 - 6 µm away from fiber tip in the axial direction. The nanorod trapped with tip contact was highly stable and stay trapped for several hours. They were aligned with the fiber axis with a residual angular distribution width of 4° at a light power of 34.8 mW. Moreover, we have determined trap stiffness of the off-tip trapped nanorod by applying the Boltzmann statistics and power spectra analysis of position fluctuations.
Subsequently, the trapped NaYF4:Eu nanorods were used for studying the Eu3+ emission spectra in two orthogonal directions: perpendicular and parallel to the nanorod axis. The influence of anisotropic polarization was observed in the perpendicular direction whereas emission remained isotropic polarization in the parallel direction. The observed emission spectra have been analyzed for the well-defined peaks at 590 and 614 nm corresponds to the magnetic and electric dipole transitions. The experimental investigations were completed by studying the polarization-dependent emission spectra in the perpendicular direction.