NaGdF4纳米晶多元醇法的合成、表征与NaGdF4：Eu3+和NaGdF4：Yb3+, Er3+纳米晶的发光

通过多元醇法(polyol method)合成出NaGdF₄:Eu³⁺和NaGdF₄:Yb³⁺,Er³⁺纳米晶,利用X射线衍射(XRD)、场发射扫描电镜(FE-SEM)和傅立叶变换红外吸收光谱(FT-IR)对合成的样品进行了表征。研究了Eu³⁺掺杂样品的下转换发光和Yb³⁺/Er³⁺共掺杂样品的上转换发光。对未经退火和经过退火的样品进行了比较。

Polyol-mediated Synthesis and Characterization of NaGdF4 Nanocrystals and luminescence properties of NaGdF4: Eu3+ and NaGdF4: Yb3+,Er3+ nanocrystals

NaGdF₄ nanocrystals were prepared using a polyol method and were characterized by powder X-ray diffraction (XRD) patterns, field emission scanning electron microscopy (FE-SEM) images and FTIR spectra. Down-conversion luminescence of NaGdF₄:1%Eu³⁺ nanocrystals and up-conversion luminescence of NaGdF₄:6%Yb³⁺,1%Er³⁺ nanocrystals were studied. Annealed samples were compared with unannealed samples. The X-ray diffraction results showed that the prepared samples were hexagonal phase of NaGdF₄. Field emission scanning electronic microscopy revealed that the average diameter was 15, 18 and several hundreds nanometers for nanocrystals unannealed, annealed at 400℃ and annealed at 600℃ respectively. After being annealed at 400℃ for 2 h, ⁵D_1-3/⁵D₀ emission intensity ratio increased remarkably for NaGdF₄:1%Eu³⁺ sample; up-conversion emission intensity increased at least by factor of 67 for NaGdF₄:6%Yb³⁺,1%Er³⁺ sample. These increases were attributed to the anneal-derived decrease of OH^- species etc. These species have high energy vibrations and can make multiphonon relaxation occur easier. The oxygen contamination is at very low level, undetectable by optical spectroscopy method in samples unannealed and annealed at 400℃, but is detectable by optical spectroscopy method in sample annealed at 600℃. Two-photon processes are involved in the green and red upconversion luminescence and three-photon are involved in the blue upconversion luminescence.