Lanthanide-doped nanoparticles (NPs) with precisely designed size and shape, as well as thoroughly characterized spectroscopic properties are attractive candidates for new types of optically active labels for microscopic techniques. Thus, establishing reliable, cheap and reproducible methods to synthesize lanthanide-doped NPs of different sizes and shapes is crucial, as the morphology can strongly influence the spectroscopic properties of those nanoluminophores [1]. Additionally, for labeling applications it is very important to precisely characterize the spectroscopic properties at a single NP level, the luminescence intensity of a single NP being one of the relevant parameters in optical imaging.

Lanthanide-doped up-converting NPs are promising candidates for microscopy labeling applications, because of the possibility to excite their characteristic emission with light from the near-infrared region, which is less susceptible to scattering and can penetrate deeper through the investigated species [2]. Such NPs also show only little photobleaching and photoblinking, and thus are promising candidates for single-particle tracking [3].

Here we report the synthesis of high-quality rare-earth  doped NaYF₄ nanowires, with the use of oleic acid as a capping agent through the microwave assisted hydrothermal technique. The utilized synthesis protocol resulted in formation of 1μm×100nm long nanowires with a high length:diameter aspect ratio. The phase, shape and size of the particles were examined with TEM and SEM imaging. Er³⁺ and Yb³⁺ co-doped nanowires excited with a 976 nm laser diode exhibited strong anti-Stokes emission peaking at 540 nm/654 nm, and Stokes emission within the conventional telecommunication C-band transmission window at 1524 nm. We have investigated the power dependence of both up- and down-conversion emission. Additionally, we have performed diffraction-limited, single-particle imaging and steady-state and time response spectroscopy of the synthesized nanowires, in order to show their suitability for various optical imaging experiments. 

References

[1] F. Zhang et al., Shape, Size, and Phase-Controlled Rare-Earth Fluoride Nanocrystals with Optical Up-Conversion Properties, Chemistry - A European Journal, 2009, 15(41), 11010–11019.

[2] F. Auzel, Chem. Rev., 2004, 104, 139–173.

[3] A. D. Ostrowski et al., Controlled Synthesis and Single-Particle Imaging of Bright, Sub-10 nm Lanthanide-Doped Upconverting Nanocrystals, ACS Nano, 2012, 6 (3), 2686–2692.