Fig. 1. (a) SEM image of NaYF4:Eu3+ nanorods. (b) SEM image and CAD drawing of the Fresnel lens fiber. (c) Schematic of the optical fiber tweezers setup.

Fig. 2. Optical trapping results. (a) PL intensity as a function of the number of nanorods in the trapped cluster. Inset: microscope photoluminescence image of a trapped nanorod. (b) Particle tracking plot for one single nanorod and clusters of two or three rods (P=32.2  mW). (c) Corresponding position (transverse and axial) and angular distributions. Inset: angular distribution width.

Fig. 3. Power spectrum analysis in axial and transverse directions for trapping of (a) one single rod and (b) a three-rod cluster. Lines are best fits to Eq. (2) (in the transverse direction, the fitting range is limited to frequencies f>2.5  Hz).

Fig. 4. Power dependent trap stiffness κ in the (a) transverse and (b) axial directions. The lines are linear fits through the origin to calculate the normalized trapping stiffness κ˜ shown in the insets as a function of number of nanorods in the trapped cluster (lines are guides to the eye; BS, Boltzmann statistics; PSA, power spectrum analysis).

Fig. 5. (a) Emission spectra of optically trapped nanorods NaYF4:Eu3+ for σ and π orientations. Inset: comparison with the emission of nanorod clusters on a glass substrate. (b) Eu3+ energy level diagram.

Fig. 6. Europium emission polarization properties. (a)–(c) Gaussian peak distribution applied for fitting the respective emission lines, (d)–(f) polar emission amplitude plots, and (g)–(j) schemes showing the respective electric and magnetic dipole orientations and main emission polarizations. The lines in the polar plots are best numerical fits to Eq. (4).

Fig. 7. (a) Photoluminescence (PL) decay for trapped nanorods at different pump powers. The lines are single exponential fits. (b) Pumper power dependent decay time. (c) PL decay for trapped nanorods and a nanorods cluster on a glass substrate.

Table 1. Transverse and Axial Normalized Trap Stiffness κ˜ Obtained by Boltzmann Statistics (BS) and Power Spectrum Analysis (PSA) and Angular Orientation Width σθ for One, Two, and Three Rods Trapped at P=32.2  mW

Table 2. Main Polar Fitting Parameters for Europium Emission Lines as Shown in Fig. 6^a