Preparation And Luminescent Performance Of Rare Earth Fluoride Nanomaterials

Rare earth elements have excellent light,electricity,magnetic properties due to their special electronic configuration,and become a treasure trove of new materials.Rare earth based nanoparticles constitute an emerging research field recognized with wide ramifications and impact in many areas ranging from security,to energy,and to healthcare.In particular,with the devolpment of the nanotechnology,many rare earth based luminescent nanomaterials with certain structure have been designed for special applications.In this paper,rare earth fluoride luminescent nanomaterials with ultrasmall size and special structure were prepared to militate cross relaxation of Ln3+ and thus improve upconversion and downconversion luminescence.The preliminary application of these nanomaterials in photodynamic therapy were expored.The main research contents are as follows:1.Dumbbell-like structured NaYF4:Yb/Er@NaNdF4:Yb nanoparticles are fabricated and applied in photodynamic therapy(PDT).The epitaxial growth along the c axis attributed to the large structure mismatch of NaNdF4 versus NaYF4 has been demonstrated to play a key role in the growth of the dumbbell structure.Due to better space separation in this structure,energy back-transfer from Er3+ to Nd3+ is prohibited partially,and the optimized Nd3+ doping concentration is up to 90%for a high UC emission intensity.PDT effects of these dumbbell-like structured UCNPs upon 800 nm laser irradiation were examined and compared with isotropic NaYF4:Yb/Er @NaYF4:Nd0.2 core-shell and NaYF4:Yb/Er@NaYF4:Nd0.2@NaYF4 core-shell-shell UCNPs.The results show that the dumbbell-like UCNPs are most effective in generating singlet oxygen(1O2)and killing cancer cells in PDT though their UC emission intensity is lower than that of the core-shell-shell UCNPs.This research presents a simple yet valid strategy to balance the UCL efficiency and FRET efficiency,which may lead to better PDT therapeutic effect for cancer therapy.2.Lanthanide ions(Ln3+)doped CaF2 luminescent nanoparticles exhibit unique optical properties and represent promising candiadates for bio-applications.However,their inherent weak luminescent intensity greatly limits their application.We have doped Ln3+ ions along with Na+ ion into CaF2 lattice to maintain charge neutrality and investigated the influence of Na+ ion on the 800 nm triggered upconversion process.As compared with Na+-free(shell layer)nanoparticles,the crystallinity,average lifetime of the excited sensitizor/activator states,and the energy transfer process from sensitizers(Nd3+)to activators(Er3+)have been improved greatly.As a result,the upconversion luminscence(UCL)intensity of Na+-codoping nanoparticles has been enhanced remarkably upon 800 nn irradiation although less Ln3+ ions were doped into CaF2 in this case.The as-synthesized CaF2:Yb/Er@CaF2:Nd/Yb core-shell structured(CS)UCNPs may be a good candidate as an excellent imaging nano-probe because of their good biocompatibility.3.As far as biomedical imaging is concerned,low upconversion luminescence and tissue autofluorescence greatly limit the application of upconversion nanoparticles.In this respect,near-infrared fluorophores such as rare earth fluorides with downconversion luminescence have attracted more and more attention.CaF2:Nd nanoparticles with about 5 nm were synthesized by thermal decomposition method.By codoping Na+ ions with Nd3+ ions,the crystallinity of the nanoparticles has been improved and the cross relaxation between Nd3+ ions has been suppressed,thus the lifetime of the excited state of Nd3+ ions has been prolonged.As a result,the downconversion luminescence intensity in the near infrared(NIR)? region(850-1400 nm)under 800 nm laser irradiation has been enhanced greatly.Besides,the downconversion luminescence intensity of the CaF2:Nd nanoparticles has been further improved by coating a passivation shell layer.Due to the ultrasmall size and high emission intensity in NIR ? region under 800 nm laser irradiation,the as-prepared CaF2:Nd nanoparticles may have potential applications in the biomedical imaging field.