Improvement in Luminescence Intensity of β-NaYF4: 18%Yb3+, 2%Er3+@β-NaYF4 Nanoparticles as a Result of Synthesis in the Presence of Stearic Acid.

Piotr Kaminski,Tomasz Grzyb,Gabriela Klima,Dominika Przybylska

doi:10.3390/nano12030319

Abstract

The synthesis of upconverting nanoparticles (NPs) is crucial for their spectroscopic properties and further applications. Reducing the size of materials to nano-dimensions usually decreases emission intensity. Therefore, scientists around the world are trying to improve the methods of obtaining NPs to approach levels of emission intensity similar to their bulk counterparts. In this article, the effects of stearic acid on the synthesis of core@shell β-NaYF4: 18%Yb3+, 2%Er3+@β-NaYF4 upconverting NPs were thoroughly investigated and presented. Using a mixture of stearic acid (SA) with oleic acid and 1-octadecene as components of the reaction medium leads to the obtaining of monodispersed NPs with enhanced emission intensity when irradiated with 975 nm laser wavelength, as compared with NPs prepared analogously but without SA. This article also reports how the addition of SA influences the structural properties of core@shell NPs and reaction time. The presence of SA in the reaction medium accelerates the growth of NPs in comparison with the analogic reaction but without SA. In addition, transmission electron microscopy studies reveal an additional effect of the presence of SA on the surface of NPs, which is to cause their self-organization due to steric effects.

Highlights

Upconverting nanoparticles (UCNPs) have become one of the most important topics in materials sciences
NaYF4 : 18%Yb3+, 2%Er3+ @β-core NaYF4 material prepared according to the above procedure without the presence of stearic acid (SA) (WSACS); the only difference of synthesis of this material was based on the change of the composition of organic solutions—1 mmol of NPs was obtained by the mixture of 10 mL of oleic acid (OA) and 10 mL of 1-ODE after thermal treatment at 300 ◦ C for 55 min
Hexagonal crystal phase, which is typical of NaREFin synthesized the reaction obtained in high boiling point positions of the reflections the X-ray diffraction (XRD) patterns of theby nanomaterials are in strong

Summary

Introduction

Upconverting nanoparticles (UCNPs) have become one of the most important topics in materials sciences. NaYF4 -based materials are usually synthesized by hydrothermal and solvothermal methods or by the reaction of high-boiling point solvents. The latter one is the most important for the synthesis of core@shell UCNPs and the most frequently used. The addition of OM as a surface capping ligand allows for the growth of nanoparticles to be controlled by changing the conversion mechanism of the cubic to the hexagonal phase [16]. SA to the reaction medium is an easy step as it does not significantly change the known methods of core@shell UCNPs synthesis. To the best of our knowledge, no previous attempts to use SA to synthesize core@shell NPs have been reported

Materials

Synthesis of Materials

Characterization of Materials

Results and Discussionstructures of the nanoparticles were determined by XRD

Luminescent Properties of NPs

Conclusions