Investigations On The Synthesis And Luminescence Of Rare Earth Gd³⁺ Doped Upconversion Luminescent Nanocrystals

ABSTRACT:Lanthanide (LN) doped upconversion luminescence nanomaterias (UCNPs) are found to be the most effective materials so far that can transfer near-infrared light into visible light, which have broad applications in the field of biological analysis, such as in biolabeling, bioimaging, and clinical treatment. However, the premise behind this study is the high emission intensity of the synthesized UCNPs, as well as the small size and water solubility in order to adapt to biological environment. To meet these requirements, Gd3+-doped upconversion luminescence nanomaterials used in vitro biolabeling were synthesized, and the increasement UC emission intensity on the premise of almost unchanged size was discussed. Furthermore, the UC properties and mechanisms were given. The main works are as follows:1、Hexagonal phase NaYF4:Yb, Er upconversion luminescent nanocrystals were prepared by solvothermal method, and the UC luminescent mechanism was explained combined with luminescence theory. The UC emission intensities can be tuned by changing the doping ratio of Y3+and Yb3+, When Yb3+doping concentration is0.18mmol, the upconversion luminescence intensity is maximum in the visible range. With further increasing the content of Yb3+doped, the upconversion luminescence intensity of NaYF4:Yb, Er upconversion luminescence nanoparticles decreases gradually. The upconversion luminescence intensity of NaYF4:Yb,Er UCNPs increases by1to2orders of magnitude compared with that of NaYF4: Er nanoparticles without Yb3+doped.2、Under the same experimental conditions, NaY/GdF4:Yb, Er upconversion luminescence nanomaterials with higher luminous intensity were prepared by doping Gd3+ions in the original synthesis system. The influence of Gd3+ion proportion on upconversion luminescence intensity was explored. When Gd3+doping proportion is0.2mmol, the upconversion luminescence intensity of NaY/GdF4:Yb, Er UCNPs is maximum. With the further increase proportion of Gd3+doped, the upconversion luminescence intensity decreases gradually. The experimental results show that the NaY/GdF4:Yb, Er upconversion luminescence nanoparticles are hexagonal, with the size of20-50nm.3、In order to improve the water solubility of NaY/GdF4:Yb, Er upconversion luminescence nanoparticles, ultrasound clearance method and silica coating process are used respectively to achieve the conversion of NaY/GdF4:Yb, Er UCNPs’ oil-solubility to water-solubility. Ultrasound for20minutes at400w ultrasonic power can significantly improve the water solubility. This method is suitable for relatively large particle size of upconversion nanocrystals. And it has the advantages of simple operating process and high success rate. Silica coating process is more suitable for a relatively small diameter of upconversion nanocrystals.