Nano-colloids and nano-crystals doped with ions of rare-earth elements have recently attracted a lot of attention in the scientific community due to their potential applications as biomarkers, fluorescent inks, gain media for lasers and optical amplifiers. Many rare-earth doped materials of different compositions, shapes and size distribution have been prepared by different synthetic methods, such as chemical vapor deposition, sol-gel process, micro-emulsion techniques, gas phase condensation methods, hydrothermal methods and laser ablation. In this paper micro-crystalline powder of the rare-earthdoped compound NaYF<sub>4</sub>:Yb<sup>3+</sup>, Er<sup>3+</sup> was synthesized using a simple wet process followed by baking in open air. Under 980 nm diode laser excitation strong fluorescence in the 100 nm band around 1531-nm peak was observed from the synthesized micro-powder. The micro-powder was pulverized using a ball mill and prepared in the form of nano-colloids in different liquids. The particle size of the obtained nano-colloids was measured using an atomic force microscope and a dynamic light scatterometer. The size of the nano-particles was close to 100-nm. The nano-colloids were utilized as a filling media in capillary optical amplifiers and lasers. The gain of a 7-cm-long capillary optical amplifier (150-micron inner diameter) was as high as 6 dB at 200 mW pump power. The synthesized nano-colloids and the active optical components using them can be potentially used in optical communication, signal processing, optical computing, and other applications.
In this paper we investigate optical properties and size distribution of the nano-colloids made of trivalent rare-earth ion doped fluorides: holmium and ytterbium, thulium and ytterbium, and erbium and ytterbium co-doped NaYF<sub>4</sub>. These materials were synthesized by using simple co-precipitation synthetic method. The initially prepared micro-crystals had very weak or no visible upconversion fluorescence signals when being pumped with a 980-nm laser. The fluorescence intensity significantly increased after the crystals were annealed at a temperature of 400°C - 600°C undergoing the transition from cubic alpha to hexagonal beta phase of the fluoride host. Nano-colloids of the crystals were made in polar solvents using the laser ablation and ball milling methods. Size analyses of the prepared nano-colloids were conducted using a dynamic light scatterometer and atomic force microscope. The nano-colloids were filled in holey PCFs and their fluorescent properties were studied and the feasibility of new a type of fiber amplifier/laser was evaluated.
Nano-colloids and nano-crystals doped with ions of rare-earth elements have recently attracted a lot of attention in
the scientific community. This attention is due to unique physical, chemical and optical properties attributed to
nanometer size of the particles. They have great potential of being used in applications spanning from new types of
lasers, especially blue and UV ones, phosphorous display monitors, optical communications, and fluorescence
imaging. In this paper we investigate the near-infrared upconversion luminescence in bulk crystals and nanocolloid
filled photonic crystal fiber with ytterbium and holmium co-doped NaYF4 phosphor. The phosphor is prepared by
using simple co-precipitation synthetic method. The initially prepared phosphor has very week upconversion
fluorescence. The fluorescence significantly increased after the phosphor was annealed at a temperature of 600 °C.
Nanocolloids of this phosphor were obtained using 1-propanol as solvent and they were utilized as laser filling
medium in photonic crystal fibers. Under 980 nm diode laser excitation very strong upconversion signals were
obtained for ytterbium and holmium co-doped phosphor at 541 nm, 646 nm and 751 nm. Pump power emissions,
laser ablation and size analysis of the particles was conducted to understand the upconversion mechanisms. The
particle sizes of the nanocolloids were analyzed using Atomic Force Microscope and Malvern Zetasizer instrument.
The reported nanocolloids are good candidates for fluorescent biosensing applications and also as a new laser filling
medium in fiber laser.