核壳结构对水性NaYF_4:Pr^(3+)@NaYF_4一阶近红外量子剪裁的增强

Enhanced First-order Near Infrared Quantum Cutting in Water-soluble NaYF_4:Pr^(3+)@NaYF_4 Core-shell Nanoparticles

采用共沉淀法成功制备出油性NaYF_4:Pr^(3+)和NaYF_4:Pr^(3+)@NaYF_4纳米颗粒,通过盐酸酸洗改性处理,获得水性NaYF_4:Pr^(3+)和NaYF_4:Pr^(3+)@NaYF_4纳米颗粒.分别采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、荧光光谱仪对纳米颗粒的结构、形貌和发光性能进行表征与分析,探究核壳结构对发光性能的影响.结果表明:制备的水性NaYF_4:Pr^(3+)和NaYF_4:Pr^(3+)@NaYF_4纳米颗粒结构均为六方相,形貌均为球状,且在水溶液中分散性良好.荧光光谱证明了在444 nm光激发下,NaYF_4:Pr^(3+)存在一阶近红外量子剪裁,其量子剪裁机制为:Pr^(3+)被激发到~3P_2并迅速无辐射弛豫至~3P_0,进而产生两步级联双光子发射~3P_0→~1G_4(915 nm)、~1G_4→3H4(990 nm).具有核壳结构的水性NaYF_4:Pr^(3+)@NaYF_4纳米颗粒相比于水性NaYF_4:Pr^(3+)纳米颗粒,其近红外量子剪裁发光强度增强了2.6倍.增强原因为NaYF_4:Pr^(3+)@NaYF_4纳米颗粒的壳层起到保护作用,使得盐酸改性处理未在发光中心附近产生缺陷.

The oleate-capped NaYF4： Pr^3＋and NaYF4： Pr^3＋@ NaYF4 nanoparticles were synthesized by co-precipitation method. The water-soluble NaYF4： Pr^3＋and NaYF4： Pr^3＋@ NaYF4 nanoparticles were obtained by hydrochloric acid modification. The structure, morphologies and luminescence properties of nanoparticles were analy zedby X-ray diffraction spectrometer（ XRD）,Scanning electron microscope（ SEM） and Fluorescence spectrometer, respectively. The effects of core-shell structure were investigated in detail. The results show that the prepare dwater-soluble NaYF4： Pr^3＋ and NaYF4： Pr^3＋@ NaYF4 nanoparticles are hexagonal phase,ball-like and can be well dispersed in water. The fluorescence spectra proved that NaYF4： Pr^3＋ has first order near infrared quantum cutting（ NIR QC） under the excitation of 444 nm（^3 H4→^3 P2）. The mechanism of NIR QC involves such a process： following fast nanoradiative relaxation from the excited ^3 P2 state to ^3 P0 state,there is a cascade emission ^3 P0→^1 G4（ 915 nm） and ^1 G4→^3 H4（ 990 nm）. The NIR QC luminescence intensity of the water-soluble NaYF4： Pr^3＋@ NaYF4 nanoparticles with core-shell structure is 2. 6 times greater than that of the water-soluble NaYF4： Pr^3＋ nanoparticles. The enhancement of quantum cutting luminescence is due to the protection of NaYF4 shell. The shell prevents the generation of defects near the luminescence centers with removing of the oleate ligand after the modification.