Ligand Assisted Phase Tuning of Lanthanide doped NaYF₄ nanoparticles at Room Temperature

Sarkar, Debashrita (2015) Ligand Assisted Phase Tuning of Lanthanide doped NaYF₄ nanoparticles at Room Temperature. Masters thesis, Indian Institute of Science Education and Research Kolkata.

PDF (MS dissertation of Debashrita Sarkar (13IP007)) Debashrita_Sarkar_13IP007.pdf - Submitted Version Restricted to Repository staff only Download (2MB)

Abstract

Lanthanide (Ln³⁺) - doped nanomaterials are of great interest due to their characteristic features like sharp emission signals, upconverting ability, longer luminescence lifetimes (μs to ms), etc. Among various host matrices NaYF₄ is found to be a superior host for Ln³⁺ ions, which is supported by large number of literature reports . NaYF₄ crystallizes in two phases α (cubic) and β (hexagonal). The β form exhibits higher luminescence efficiency compared to α phase. There are quite a few reports available on different synthetic techniques for Ln³⁺ doped NaYF₄ nanoparticles like thermal decomposition, hydrothermal route, microwave irradiation, co-precipitation, etc. These techniques usually utilize carcinogenic precursors and often produce hazardous side products along with the nanoparticles. Thus it is a challenge to develop greener synthetic methods to make these materials. In this thesis we demonstrated a greener approach for the synthesis of colloidal NaYF₄ nanoparticles using water and ethanol mixture as solvent at room temperature (25⁰C) for the first time. The dispersibility of the nanoparticles was achieved by capping with several organic molecules onto the surface of nanoparticles. Interestingly capping agents play a crucial role in determining the morphology, size as well as the phase of the nanoparticles. The nanoparticles were characterized by Powder X-Ray Diffraction (PXRD), Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). To make the materials luminescent, Ln³⁺ ions (Eu³⁺, Yb³⁺/Er³⁺) were doped into NaYF₄ nanoparticles. Ln³⁺-doped NaYF₄ nanoparticles synthesized at room temperature show high luminescence efficiency which generally necessitates materials to be prepared at high temperatures.

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