Rapid Microwave Synthesis And Application Of Nd³⁺-doped β-NaYF₄/NaGdF₄ Nanoparticles With Near-infrared Luminescence

Rare-earth(RE) doped NaYF4 nanoparticles, widely used in the fields of materials, chemical industry, biology and clinical medicine, have been attracting great attention owing to their superior properties of high refractive index, excellent photostability, low phonon energy and low energy radiation. However, some constraints, especially the larger overheating affect on tissue damage upon excitation at 980 nm, weaker near-infrared(NIR) luminescence, lower resolution imaging and lower light penetration through organism tissue limit the development and utilization of the NaYF4 materials. Hence, this paper has successfully prepared Nd3+-doped β-NaYF4/NaGdF4 nanoparticles by simple and facile method. The results demonstrated that obtained materials possessed the fluorescence imaging function with strong near-infrared(NIR) emission under NIR excitation. The main contents and novelty were summarized as follows:1. In this work, we reported a simple, rapid way to synthesize NaYF4:Nd3+ materials. Notably, cubic(α-) and hexagonal phase(β-) NaYF4:Nd3+ were rapidly prepared by a microwave method. Moreover, the effect of the microwave power, reaction temperature, and the mole ratio of NaF/Ln3+ on the phase structure, particle size and luminescence properties was also investigated in detail. Interestingly, XRD、SEM indicated that when the mole ratio of NaF/Ln3+ was 2.3:1, α-NaYF4:Nd3+ nanospheres with 130 nm were obtained by heated for 2 min at the microwave power of 600 W, and hexagonal β-NaYF4:Nd3+ nanophosphors with a mean diameter of 200 nm were prepared by heated for 5 min at the microwave power of 600 W and then 13 min of 300 W. Compared with the hydrothermal method, their luminescent intensities of the products by the microwave synthesis were significantly stronger and the microwave method allowed for a large reduction of preparation time, making it possible to obtain pure β-NaYF4:Nd3+ nanoparticles within only 18 min compared to several hours by the traditional hydrothermal synthesis. The major advantages of the microwave method include simple preparation, rapid heating speed, short reaction time and strong NIR luminescence.2. Nd3+-doped β-NaYF4 nanophosphors were obtained via optimizing microwave method. The effect of materials on the phase structure, particle size, NIR luminescence and application on fluorescence imaging was explored. It was observed that nanoparticles exhibited efficient NIR luminescence of Nd3+ from 810 to 1058 nm at 808 nm excitation. When the Nd3+ content was 0.5%, the NIR emission was the strongest. To obtain a clear high-resolution imaging, camera filter, aperture size and exposure time were typically optimized on experiment. The simple camera could be observed the NIR fluorescence imaging of 10 mg/m L β-Na YF4:0.5%Nd3+ through 2 cm thickness pork upon excitation at 808 nm. This study established a typical model of NIR fluorescence imaging based on β-NaYF4:Nd3+ excited at 808 nm, which was expected to be developed into a promising tool for the efficient vivo imaging, biological testing and medical diagnosis.3. Pure β-NaGdF4:Nd3+ nanophosphors were successfully prepared by the microwave synthesis method. Their NIR luminescence properties were investigated in detail. It is found that the NIR emission from β-NaGd F4:2%Nd3+ was the strongest upon excitation at 808 nm by controlling the doping Nd3+ content to 2%. Vibrating sample magnetometer(VSM) confirmed magnetic properties. The results showed that its magnetization of β-NaGdF4:Nd3+ materials gradually reduced with increase of the Nd3+ doping concentration. The NIR fluorescence imaging experiments under the simple camera indicated that 10 mg/mL β-NaGdF4:2%Nd3+ could penetrate through 1 cm thickness pork upon excitation at 808 nm. In addition, owing to the unique magnetic and NIR luminescence properties, β-NaGdF4:Nd3+ nanomaterials could serve as an important basis and reference on the fluorescence imaging, bio-separation and magnetic resonance imaging.