Enhanced dye-sensitized up-conversion luminescence of neodymium-sensitized multi-shell nanostructures
doi: 10.37188/CO.2020-0097
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摘要: 对于稀土离子掺杂的上转换发光，由于稀土离子吸收截面小、吸收范围窄，导致其发光强度受限。最近，在稀土上转换纳米粒子的表面连接近红外染料分子敏化发光，被证实是提高上转换发光强度的有效策略。然而，将染料分子连接经典的稀土Yb掺杂纳米粒子，并不能有效利用染料分子的敏化能力。针对这一问题，本文通过高温热分解法成功制备了Nd3+敏化的核/壳/壳 (NaYF4:Yb/Er (20/2%)@ NaYF4:Yb (10 %)@ NaYF4:Nd (80 %))纳米结构，与经典的IR-806敏化的NaYF4:Yb/Er纳米结构相比，IR-806敏化的Nd3+掺杂的核/壳/壳纳米结构的上转换发光(500~700 nm)强度增强了约38倍。通过荧光光谱及荧光寿命分析证实，上转换发光强度增强源于Nd的吸收与近红外染料分子的有效交叠，以及壳层结构对发光中心的保护作用(Er3+ (4S3/2→4I15/2)的寿命延长了1.7倍)。另外，研究发现纳米壳层结构中最外层掺杂的Yb3+离子将导致染料敏化发光减弱。进一步，这种IR-806敏化的Nd掺杂的核/壳/壳纳米结构可实现增强发光中心为Ho及Tm的上转换发光。本文研究为提高染料敏化上转换发光及应用提供了新途径。Abstract: Lanthanide-ion-doped upconversion luminescence is limited by the small absorption cross-section and narrow absorption band of lanthanide ions, which results in weak luminescence. Recently, a dye-sensitized method has proven to be an effective strategy of increasing upconversion luminescence. However, simply attaching dye molecules to nanoparticles with classic Yb-doped nanostructures cannot effectively activate the sensitizing ability of the dye molecules. In response to this problem, we designed Nd-sensitized core/shell/shell (NaYF4:Yb/Er (20/2%)@ NaYF4:Yb (10 %)@ NaYF4:Nd (80 %)) nanostructures, compared with the classic IR-806 sensitized NaYF4:Yb/Er nanostructure, their upconversion luminescence (500 to 700 nm) was approximately enhanced by a factor of 38. Through analysis of the nanostructure’s emission and luminescence lifetime data, the enhancement was confirmed by the effective overlap of Nd absorption with the emission of near-infrared dye molecules and the protective effects of the shell structure on the luminescent center (the lifetime of Er (4S3/2→4I15/2) was increased by 1.7 times). In addition, we found that the doping Yb3+ in the outermost layer will decrease the dye-sensitized luminescence intensity. Furthermore, this Nd-sensitized core/shell/shell structure also achieved enhancement in the sensitized upconversion luminescence of the luminescence centers of Ho and Tm, which establishes a foundation for enhanced dye-sensitized upconversion luminescence.
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Key words:
- upconversion luminescence /
- dye-sensitized /
- lanthanide ion /
- nanoparticles
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图 1 上转换纳米粒子的核（a），核/壳（b），核/壳/壳（c）电镜表征图及尺寸分布（d）
Figure 1. TEM images of core (a), core/shell (b) and core/shell/shell (c) of up-conversion nanoparticles and their size distributions (d)
图 2 （a）上转换纳米粒子的核、核/壳、核/壳/壳XRD及标准卡片β-NaYF4 (JCPDS-16-0334, 底部)结果，（b）上转换CSS的EDS数据，（c）IR-806 合成过程图，（d）合成前后IR-780 和 IR-806的吸收，（e）连接IR-806之后UCNPs吸收和UCNPs本身的吸收
Figure 2. (a) XRD data of C, CS and CSS of UCNPs and the β-NaYF4 (JCPDS-16-0334, bottom); (b) EDS data of CSS; (c) IR-806 synthesis process; (d) absorptions of IR-780 and IR-806 before and after synthesis; (e) absorption of UCNPs and dye conjugated UCNPs after IR-806 connection
图 3 （a）IR-806敏化CSS结构的上转换光谱及IR-806敏化核结构的上转换光谱，激发波长为808 nm，（b）808 nm激发下的IR-806敏化的CSS结构的上转换发光强度随功率变化的log-log关系
Figure 3. (a) Up-conversion luminescence (UCL) spectra of IR-806-sensitized CSS structure and IR-806-sensitized core structure under 808 nm excitation wavelength; (b) log-log plots of the UCL intensity versus laser power for the IR-806 dye-sensitized CSS under 808 nm excitation
图 4 （a）IR-806分子的发射光谱与Nd3+的吸收交叠图；（b） 980 nm激发下，测试得到的核纳米粒子（黑色, NaYF4: Yb/Er (20/2%)），染料敏化核纳米粒子（红色）及染料敏化的CSS纳米结构（蓝色）的Er3+ (4S3/2→4I15/2)的寿命测试结果；（c）808 nm激发下CSS纳米结构及染料敏化的CSS纳米结构的Er3+ (4S3/2→4I15/2)的寿命测试结果
Figure 4. (a) Overlap between the emission spectrum of IR-806 molecules and the absorption spectrum of Nd3+; (b) the lifetimes of Er3+ (4S3/2→4I15/2) in core nanoparticles (black, NaYF4:Yb/Er (20/2%), dye-sensitized core nanoparticles (red) and dye-sensitized CSS nanostructure (blue) under 980 nm excitation; (c) the lifetimes of Er3+ (4S3/2→4I15/2) in CSS nanostructure and dye-sensitized CSS nanostructure under 808 nm excitation
图 5 染料敏化的NaYF4:Yb/Er (20/2%)@ NaYF4:Yb (10%)@ NaYF4:Nd/Yb (80/x%) (x=0, 5, 10, 20)的上转换光谱（808 nm激发）
Figure 5. Upconversion spectra of dye-sensitized NaYF4:Yb/Er(20/2%)@ NaYF4:Yb (10%)@ NaYF4:Nd/Yb (80/x%) (x=0, 5, 10, 20) nanoparticles under 808 nm excitation
图 6 （a）IR-806敏化Ho核结构及IR-806敏化Ho-CSS结构的上转换光谱，（b） IR-806敏化Tm核结构及IR-806敏化Tm-CSS结构的上转换光谱，（c） 808 nm激发下的IR-806敏化的Ho-CSS结构的上转换发光强度随功率变化的log-log关系，（d） 808 nm激发下的IR-806敏化的Tm-CSS结构的上转换发光强度随功率变化的log-log关系
Figure 6. (a) The UCL of the IR-806 sensitized Ho core nanostructure and IR-806 sensitized Ho-CSS nanostructure, (b) the UCL of the IR-806 sensitized Tm core nanostructure and IR-806 sensitized Tm-CSS nanostructure, (c) log-log plots of the UCL intensity over laser power for the green and red emissions of the dye-sensitized Ho-CSS under 808 nm excitation, (d) log-log plots of the UCL intensity versus laser power for the green and red emissions of the dye-sensitized Tm-CSS under 808 nm excitation
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