We synthesized Gd2O3 and Gd2O3 doped by europium (Eu) (2% to 10%) nanoplatelets using the polyol chemical method. The synthesized nanoplatelets were characterized by X-ray diffraction (XRD), FESEM, TEM, and EDX techniques. The optical properties of the synthesized nanoplatelets were investigated by photoluminescence spectroscopy. We also studied the magnetic resonance imaging (MRI) contrast enhancement of T1 relaxivity using 3 T MRI. The XRD for Gd2O3 revealed a cubic crystalline structure. The XRD of Gd2O3:Eu3+ nanoplatelets were highly consistent with Gd2O3 indicating the total incorporation of the Eu3+ ions in the Gd2O3 matrix. The Eu doping of Gd2O3 produced red luminescence around 612 nm corresponding to the radiative transitions from the Eu-excited state 5D0 to the 7F2. The photoluminescence was maximal at 5% Eu doping concentration. The stimulated CIE chromaticity coordinates were also calculated. Judd-Ofelt analysis was used to obtain the radiative properties of the sample from the emission spectra. The MRI contrast enhancement due to Gd2O3 was compared to DOTAREM commercial contrast agent at similar concentration of gadolinium oxide and provided similar contrast enhancement. The incorporation of Eu, however, decreased the MRI contrast due to replacement of gadolinium by Eu.
The different synthesized PLNPs presented before are usually in the range of 40-150 nanometers with a polydispersed size distribution. The main reason for the polydispersity is due to non-control over the nanoparticle growth stage and agglomeration in commonly used hydrothermal or sol-gel synthetic procedures. Therefore, there was a need to develop new synthesis approaches for persistent luminescent NPs with size control. In 2015 Mao and co-workers reported the first successful synthesis of sub-ten nanometer persistent luminescent Cr doped ZnGa2O4 NPs via a biphasic hydrothermal route . In their work, the authors used a biphasic hydrothermal approach for the synthesis of Cr doped ZnGa2O4 NPs with controlled size through the hydrolysis of corresponding inorganic salts in a water-toluene system. The synthetic procedure is shown in Figure a. Typically, Zn(NO3)2, Ga(NO3)3, Cr(NO3)3 (0.2 mol% with respect to Ga) were dissolved in water, followed by the addition of -butylamine to adjust the pH of the solution to the desired value, and then stirred for 30 minutes. After that, the solution was mixed with an organic solution of oleic acid and toluene. The resulting mixture was transferred to a 45 mL Teflon-lined stainless steel autoclave in ambient environment without stirring. The sealed autoclave was heated at 160°C for 24 hours (Figure a). The purified products were separated by centrifugation and can be easily re-dispersed in a variety of nonpolar solvents (e.g., toluene, hexane, and chloroform) and show transmission electron microscopy (TEM) images of the as-synthesized Cr:ZnGa2O4 NPs (Figure b). These images clearly show that these NPs are nearly monodisperse with sub-10 nm size (6 nm). The crystal phase was further confirmed by XRD (Figure c). Such particles have the same optical characteristics as the previous larger ones in term of excitation/emission properties (Figure d) and display persistent luminescence decay (Figure e) .
Here, a ternary europium complex with 2-(4-bromomethyl)- phenylpropionic acid (BMPPA) and 2, 2'-bipyridyl (BPy) ligands was newly synthesized, which was then connected with poly (4-vinylpyridine) (P4VP) functionalized silica nanoparticles (nano- SiO2P4VP) an addition reaction to produce luminescent nanoSiO2P4VPEuBPy composites. These nanocomposites were characterized by using UV-vis absorption and infrared spectra, thermogravimetric (TG), X-ray photoelectron spectroscopy (XPS), and transmission electron microscope (TEM). Fluorescence emission spectra revealed typical Eu(III) ion emissions at the wavelengths from 580 nm to 750 nm designated to the 5D0→7Fn transitions with the emission lifetime of approximately 0.204 and 0.576 ms for the nanoSiO2EuBPy composites, and that of approximately 1.47 ms for the Eu-complex in chloroform solutions.