Ahmad Shahzad, Nagarajan Rajamani, Raj Packiya, Prakash G Vijaya
Materials Chemistry Group, Department of Chemistry, University of Delhi , Delhi 110007, India.
Inorg Chem. 2014 Oct 6;53(19):10257-65. doi: 10.1021/ic5013022. Epub 2014 Sep 25.
Fluorite structured nanocrystals of RbGdF4 in cubic symmetry have successfully been synthesized by employing a simple, one-step, and template-free wet chemical method at room temperature. Considering the structural model of cubic KLaF4 in the Fm̅3m space group, the observed powder X-ray diffraction (PXRD) pattern was fitted by the Le Bail procedure with the cubic lattice constant of a = 5.8244 (1) Å. Both high-resolution transmission electron microscopic (HR-TEM) and dynamic light scattering (DLS) measurements revealed the monodispersity of the nanocrystals with their size in the range of 2-18 nm. Upon excitation at 980 nm, Yb(3+), (Er(3+)/Ho(3+)/Tm(3+)) codoped RbGdF4 nanocrystals showed multicolor upconversion including red, yellow, blue, and the combination of basic color (near-white) emissions. Also, near-white upconversion emission from Yb(3+), Ho(3+), Tm(3+) triply doped cubic RbGdF4 nanocrystals was observed at varying laser power densities. RbGdF4 nanocrystals exhibited superparamagnetic behavior with a molar magnetic susceptibility of 2.61 × 10(-2) emu·Oe(-1)·mol(-1) at room temperature, while at low temperature (5 K) a saturation magnetization value of 90.41 emu·g(-1) at an applied field of at 10 kOe was observed. Non-interaction of the localized magnetic moment of Gd(3+) ions in the host matrix has been reasoned out for the observed superparamagnetic behavior. From the Langevin fit of the magnetic data, the average particle diameter obtained was approximately 2.2 nm, matching well with the values from other measurements. RbGdF4 nanocrystals exhibited a large ionic longitudinal relaxivity (r1 = 2.30 s(-1)·mM(-1)), suggesting their potential applicability as a promising agent for T1 contrast magnetic resonance imaging (MRI) in addition to the applications arising from the coupling of optical and magnetic functions such as multiplexing biodetection, bioimaging (optical and MRI), and other optical technologies.
通过在室温下采用简单、一步且无模板的湿化学方法，成功合成了具有立方对称性的RbGdF4萤石结构纳米晶体。考虑到Fm̅3m空间群中立方KLaF4的结构模型，通过Le Bail程序对观察到的粉末X射线衍射（PXRD）图谱进行拟合，得到立方晶格常数a = 5.8244 (1) Å。高分辨率透射电子显微镜（HR-TEM）和动态光散射（DLS）测量均表明纳米晶体具有单分散性，其尺寸范围为2-18 nm。在980 nm激发下，Yb(3+)、(Er(3+)/Ho(3+)/Tm(3+))共掺杂的RbGdF4纳米晶体表现出多色上转换，包括红色、黄色、蓝色以及基本颜色组合（近白色）发射。此外，在不同激光功率密度下，观察到Yb(3+)、Ho(3+)、Tm(3+)三重掺杂的立方RbGdF4纳米晶体的近白色上转换发射。RbGdF4纳米晶体在室温下表现出超顺磁性行为，摩尔磁化率为2.61 × 10(-2) emu·Oe(-1)·mol(-1)，而在低温（5 K）下，在10 kOe的外加磁场中观察到饱和磁化强度值为90.41 emu·g(-1)。已推断出基质中Gd(3+)离子的局域磁矩之间的非相互作用是观察到的超顺磁性行为的原因。通过对磁性数据的朗之万拟合，得到的平均粒径约为2.2 nm，与其他测量值吻合良好。RbGdF4纳米晶体表现出较大的离子纵向弛豫率（r1 = 2.30 s(-1)·mM(-1)），这表明除了光学和磁功能耦合所产生的应用（如多重生物检测、生物成像（光学和MRI）以及其他光学技术）外，它们还具有作为T1对比磁共振成像（MRI）的有前景试剂的潜在适用性。
