Tessitore Gabriella, Mudring Anja-Verena, Krämer Karl W
University of Bern, Department of Chemistry and Biochemistry Freiestrasse 3 3012 Bern Switzerland
Concordia University, Department of Chemistry and Biochemistry 7141 Sherbrooke W. H4B1R6 Montreal QC Canada.
RSC Adv. 2019 Oct 29;9(60):34784-34792. doi: 10.1039/c9ra05950d. eCollection 2019 Oct 28.
Sub-10 nm β-NaGdF:18% Yb,2% Er nanoparticles were synthesized in ethylene glycol and various ionic liquids under microwave heating. The products were characterized by powder X-ray diffraction, electron microscopy, and upconversion (UC) luminescence spectroscopy. After Yb excitation at 970 nm, Er ions are excited by energy transfer upconversion and show the typical green and red emission bands. The UC luminescence intensity was optimized with respect to reactant concentrations, solvents, and reaction temperature and time. The strongest UC emission was achieved for sub-20 nm core-shell nanoparticles which were obtained in the ionic liquid diallyldimethylammonium bis(trifluoromethanesulfonyl)amide from a two-step synthesis without intermediate separation. Strictly anhydrous reaction conditions, a high fluoride/rare earth ion ratio, and a core-shell structure are important parameters to obtain highly luminescent nanoparticles. These conditions reduce non-radiative losses due to defects and high energy acceptor modes of surface ligands. A low power excitation of the core-shell particles by 70 mW at 970 nm results in an impressive UC emission intensity of 0.12% compared to the bulk sample.
在微波加热条件下，于乙二醇和各种离子液体中合成了尺寸小于10纳米的β-NaGdF:18% Yb,2% Er纳米颗粒。通过粉末X射线衍射、电子显微镜和上转换（UC）发光光谱对产物进行了表征。在970纳米处对Yb进行激发后，Er离子通过能量转移上转换被激发，并显示出典型的绿色和红色发射带。对上转换发光强度进行了反应物浓度、溶剂以及反应温度和时间方面的优化。对于在离子液体二烯丙基二甲基铵双（三氟甲磺酰）酰胺中通过两步合成法获得的、无需中间分离的亚20纳米核壳纳米颗粒，实现了最强的上转换发射。严格的无水反应条件、高氟化物/稀土离子比以及核壳结构是获得高发光纳米颗粒的重要参数。这些条件减少了由于表面配体的缺陷和高能受体模式导致的非辐射损失。与块状样品相比，在970纳米处以70毫瓦对核壳颗粒进行低功率激发时，可产生令人印象深刻的0.12%的上转换发射强度。
