以柠檬酸三钠为螯合剂，采用共沉淀和水热相结合的方法成功制备出尺寸为40 nm的NaYF4∶Yb3+, Er3+纳米粒子。将得到的部分样品在300 ℃氮气保护下退火2 h。退火前后的样品晶体结构都属于立方相，尺寸保持在40 nm左右。在980 nm光激发下，退火后样品的上转换发光整体强度和绿光相对发射强度明显增强。分析认为高温退火改善了纳米粒子的结晶质量并降低了纳米粒子表面有机配体的浓度，改善了样品上转换发光性能。Luminescence of NaYF4∶Yb3+, Er3+ Nanoparticles

NaYF4∶Yb3+, Er3+ nanoparticles with the size about 40 nm were successfully prepared by the combination of coprecipitation and hydrothermal methods using trisodium citrate as chelator. The obtained sample was divided into two parts, one of them was annealed in nitrogen at 300 ℃ for 2 h. The crystal structure of the NaYF4∶Yb3+, Er3+ nanoparticles before and after annealing treatment are in cubic phase, the size of which is about 40 nm. Under the excitation of 980 nm laser, the total upconversion luminescence intensity and the relative green emission intensity of the sample after annealing is much stronger than that of the sample without annealing treatment. It is found that high temperature annealing improved the crystallization of the sample and reduced the concentration of the organic molecules on the surface of the nanoparticles, resulting in a great improve of the upconversion luminescence property.