Synthesis Of 808 Nm Excited Upconversion Nanoparticles And Photodynamic Application

In recent years,lanthanide-doped upconversion nanoparticles?UCNPs?are gradually being recognized as a new type of nano-luminescent materials.Compared to organic dyes and quantum dots,they have a unique advantage.But there are disadvantages of low fluorescence emission intensity?UCL?and low quantum yield.Most UCNPs are excited by 980 nm laser,due to the absorption of water at 980 nm,it will inevitably cause thermal effect,which can damage the normal biological tissue and limit its application in biomedical field.There are two relatively contradictory influencing factors in photodynamic therapy?PDT?:?1?UCL of UCNPs?2?fluorescence resonance energy transfer?FRET?efficiency.Most research work introduces the shell structure to increase the UCL,which can reduce UCL caused by cross-relaxation;however,the thick shell structure inevitably leads to an increase in the distance between the UCNPs and photosensitizers,FRET efficiency is reduced and it is bad to the generation of singlet oxygen?¹O₂?.In this study,we use an 808 nm laser to excite UCNPs,a new three-doped(Yb³⁺/Er³⁺/Nd³⁺)nanoparticles NaYF4:Yb/Er/Nd was prepared by thermal decomposition.Firstly,we change the concentrations of Yb³⁺and Nd³⁺dopants to enhance the intensity of I_r/g,which can make UCNPs activate methylene blue?MB?efficiently through FRET.Then a unique method was developed to prepare core-shell nanoparticles with different shell thicknesses by changing the amount of core.The UCL intensity could increase with the shell thickness decreasing.UCNPs and MB were stably encapsulated by SiO₂ through a facile water-in-oil microemulsion polymerization.With the decrease of the thickness of the shell,the FRET efficiency increased from 37.1%to 86.7%.High UCL efficiency and the efficient FRET between UCNPs and photosensitizers were simultaneously achieved to efficiently produce ¹O₂.In order to achieve high UCL,we have constructed a new structure,which uses Nd³⁺as the matrix element in the shell,it can achieve high concentration of doping?90%?to capture more 808 nm photons;In addition,Nd³⁺and Er³⁺separation can avoid energy transfer between them to achieve a stronger UCL.