- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Enhanced upconversion luminescence in NaYF<sub>4</sub>:Yb,Er nanoparticles by using graphitic carbon shells
摘要： Upconversion nanoparticles (UCNPs) have drawn much attention in the past decade due to their superior physicochemical features and great potential in biomedical. However, practical applications of upconversion luminescence are often limited by its relatively low luminescence efficiency. In this paper, we designed and synthesized NaYF4:Yb,Er nanoparticles using a hydrothermal approach, and thereafter it was coated with a thin layer of graphitic carbon to form a core/shell nanostructure via a controlled chemical vapor deposition process. It is shown that Yb and Er doped in the crystal of NaYF4 in the forms of Yb3+ and Er3+. The thickness of the graphitic carbon shell is close to 0.45 nm, and this corresponds between one and two atomic layers. The graphitic carbon shell not only leads to a significant enhancement in the emission intensity but also provide a longer luminescence decay lifetime compared to bare NaYF4:Yb,Er nanoparticles. Our finding provides a new strategy to remarkably improve fluorescence upconversion, and opportunities for diverse applications requiring high fluorescence intense.
关键词： Functional application,Optical properties,Nanocomposites,Gas phase reaction
更新于2025-09-23 15:22:29
-
Importance of carbon-monoxide-induced reaction in microwave heating synthesis of β-SiC from silicon powder in air
摘要： Microwave heating is known to provide extremely rapid synthesis of silicon carbide (SiC) from mixtures of silicon and carbon powders. The formation mechanism has long been considered to be a solid-state reaction among the powders in the mixture. Here, we present a new reaction mechanism via a gas-phase route. We have confirmed successful synthesis of ￠-SiC powder by microwave-heating of a small amount of Si powder that was entered into a quartz tube and then embedded in graphite powder, although no direct contact between the Si and graphite powders was allowed. Scanning electron microscopy observations revealed that the ￠-SiC powder was formed by direct carbonization of the Si powder. Since the atmosphere during the reaction comprises a vast majority of carbon monoxide (CO) gas according to the Boudouard equilibrium, the carbonization appears to have taken place via the CO gas. The contribution of such a gas-phase reaction could account in part for the rapidity of the microwave-heating reactions reported so far, which can hardly be explained solely by solid-state reactions among the mixed powders.
关键词： Carbon monoxide,Gas-phase reaction,Microwave heating,Silicon carbide,Air atmosphere,Silicon
更新于2025-09-23 15:21:21