Research On Fluorescence Properties Of NaYbF₄:Tm@NaYF₄ And NaYF₄:Nd@NaGdF₄@SiO₂@Au Nanocrystalline Cored-shell Structures

In the basic research and subsequent applications of up-conversion,the control of particle size,particle size distribution and excitation/emission wavelength are indispensable.The general crystal growth process is mostly in accordance with Oswald ripening process.In the first part of this paper,we found that digestion and ripening in rare earth doped ternary fluorinated system mediated the growth of core-shell nanostructures,which is contrary to the traditional Oswald ripening process.Subsequently,in order to better confirm this phenomenon,we systematically studied the size evolution of NaYb F₄:Tm@NaYF₄ nanoparticles with time,and proposed a growth mechanism involving Ksp to better understand this abnormal phenomenon.At the same time,we also found that when NaYF₄ coating was coated on the crystal surface,the intensity of up-conversion luminescence(UCL)and the branching ratio of near infrared to visible light(NIR/VIS)increased sharply,but the intensity of up-conversion luminescence and the branching ratio of near infrared to visible light decreased with SiO₂ coating.In order to further explore this phenomenon,this paper further constructs the alternating types of core-shell-shell nanostructures,namely NaYb F₄:Tm@SiO₂@NaYF₄ and NaYb F₄:Tm@NaYF₄@SiO₂,the UCL intensity and NIR/VIS ratio are both opposite.Using the steady-state and transient spectral data of NaYb F₄:Tm,and the comparative analysis of alternate coating of SiO₂ and NaYF₄nanoshells,it is shown that once the optical behavior of the surface state of the nanoshells is controlled,the properties of up-conversion luminescence can be achieved through core-shell engineering to adjust.This result provides a promising alternative strategy for the preparation of uniform core-shell nanostructures,and it also provides a promising prospect for the follow-up clinical application of up-conversion luminescence biological tissue imaging.At the same time,compared with the NIR-I region,the NIR-II region has a deeper penetration depth of biological tissue,which is one of the hot spots in the field of nanoptronics.In the outermost layers of the composite coating a layer of Au shell nanomaterials,because of the surface plasmonic resonance effect of gold nanocrystals,that is,the absorption energy coupling lattice phonons emit heat under the excitation near SPR.This material can be used in many aspects such as tumor treatment.Therefore,gold nanomaterials with the luminescence of NIR-II have a good development prospect in cancer treatment and bioluminescent medical imaging.Therefore,NaYF₄:Nd@NaGdF₄@SiO₂@Au nanocrystals was further synthesized in this paper,through core-shell coating structure to further optimize the luminescence properties of the material,the synthesized material can not only achieve the luminescence of NIR-II,at the same time,the outer layer of the material coated with Au shell,not only increase the intensity of its luminescence,but also greatly reduce its biological toxicity.And it has a series of properties of@Au shell,which is conducive to the study of subsequent biological experiments.