水溶性NaYF4：Yb，Er上转换发光纳米粒子的可控合成与发光性能研究

采用溶剂热法合成出尺寸小于30 nm的NaYF4：Yb, Er上转换纳米晶，用柠檬酸（CA）做表面活性剂使得产物具有良好的水溶性。实验探索得出NaOH或者CA的加入量能够调节溶液中能与稀土离子络合的有效配位基团-COO-的浓度，进而影响NaYF4从立方相到六方相的相变过程、实现产物形貌的控制和上转换发光性能的调变。逐渐提高NaOH的加入量，产物从30 nm的α-NaYF4：Yb, Er纳米粒子转变为尺寸300 nm 的β-NaYF4：Yb, Er 微球。提高CA 的加入量同样会促进β-NaYF4：Yb, Er微球的形成。还研究上述不同合成条件下，不同形貌结构的产物的上转换发光性能。

Controllable synthesis of water-soluble NaYF 4:Yb,Er upconversion nano-particles and their luminescent properties

NaYF4: Yb, Er upconversion nanoparticles with the size of around 30 nm were fabricated through solvothermal method. The appliation of citric acid (CA) enables the good water solubility. The results indicate that the dosage of NaOH or CA determines the concentration of -COO- group, which is acted as an effective coordinating group of rare earth ion. It further tune cubic to hexagonal phase transformation and realize the morphology control and luminescent properties tuning. With an increased amount of NaOH, the product change from 30 nm sized α-NaYF4: Yb, Er nanoparticles to 300 nm sized β-NaYF4: Yb, Er submicrospheres. An increased amount of CA promotes the formation of β-NaYF4: Yb, Er as well. Moreover, the up-conversion luminescent properties of these products with different morphologies are studied.