NaYF4: Yb,Er@SiO2的高温相变及上转换

通过固-液热分解法合成平均尺寸为27 nm的六方相NaYF₄: Yb, Er上转换纳米晶。制备了NaYF₄: Yb, Er@SiO₂核壳纳米粒子, 壳层厚度约为8 nm。将NaYF₄: Yb, Er@SiO₂分别在不同高温下焙烧3 h, 发现600 ℃下产物物相未发生变化, 但向非晶态过渡; 700、800 ℃下NaYF₄内核与SiO₂壳层发生化学反应, 产物物相均转变为NaYSiO₄。样品均用980 nm红外激光进行激发, 显示出强烈的可见光上转换发射。以初始NaYF₄: Yb, Er@SiO₂的上转换发光强度为对比样, 随着焙烧温度的升高, 样品的发光强度依次提高。这与理论上低声子能量的氟化物发光强度更高不符, 可能原因是高温处理后样品去除了部分晶格缺陷和有机杂质。 

Phase transition and upconversion luminescent properties of NaYF4:Yb,Er@SiO2 at high temperature

Hexagonal phase NaYF₄:Yb,Er upconversion nanocrystal with the size of around 27 nm were fabricated via solid-liquid thermal decomposition method.NaYF4:Yb,Er@SiO₂ core-shell nanoparticles were prepared,with the thickness of shell layer about 8 nm.NaYF₄:Yb,Er@SiO₂ were annealed at different temperatures for 3 h respectively.The hexagonal phase NaYF4 transited to amorphous phase instead of other phase as the annealing temperature increased to 600℃.When it further increased to 700℃or 800℃,the NaYF4 reacted with SiO₂ shell and formed a new phase,NaYSiO₄.The samples were excited by the 980 nm infrared laser and showed strong visible upconversion emission.The original NaYF₄:Yb,Er@SiO₂ were taken as comparison samples,the luminescence intensity of samples increased successively with the increase of annealed temperature.This is not consistent with the higher luminescence intensity of fluoride with low phonon energy.The possible reason is that some lattice defects and organic impurities were removed from the samples annealed at high temperature.