Room temperature synthesis and formation process of α-NaYF₄ nanocubes

Abstract

In this article, α-NaYF₄ nanocubes were synthesized with a simple and environmentally friendly method at room temperature. The structure and morphology of the products were characterized by X-ray diffraction and scanning electron microscopy. The influence of the F⁻/Y³⁺ molar ratio on the morphology of the products was examined. The products changed from spherical nanocrystals to cubic nanocrystals when the F⁻/Y³⁺ molar ratio gradually increased from 4:1 to 16:1, and excessive F⁻ ions were necessary for the formation of regular NaYF₄ nanocubes in our synthesis procedure. The formation process of these α-NaYF₄ nanocrystals was traced via time-dependent experiments. Several nanometer-sized NaYF₄ nanocrystals changed into 100 nm sized NaYF₄ nanocrystals with prolonging of the reaction time. Additionally, the photoluminescence properties of Eu³⁺-doped samples were investigated. The excitation spectrum consists of the characteristic absorption peaks of Eu³⁺ corresponding to the direct excitation from the europium f-electrons. The charge-transfer band of Eu³⁺–F⁻ is not present in our measured range. The ⁵D₀ → ⁷F₁ transition is much stronger than the ⁵D₀ → ⁷F₂ transition in our samples.