The Effect Of Ba₂LnF₇ (Ln=Y,La) Nanocrystalline Structure In Glass On The Upconversion Luminescence Properties

In recent years,lanthanum doped oxyfluoride glass-ceramics have emerged,and by adjusting the glass composition and heat treatment conditions,oxyfluoride crystallites are precipitated in a glass matrix,and the advantages of both crystals and glass are solved.A series of problems such as high efficiency light emission,high transmittance,and high stability.Therefore,oxyfluoride glass-ceramics can be referred to as a very promising lanthanide-doped luminescent material,which has been widely used in solid-state lasers,fiber amplifiers,LEDs,and three-dimensional display.Ever since,scientific researchers have been paying attention to the luminescent efficiency of rare earth luminescent materials.The up-conversion luminescence efficiency of glass-ceramics is mainly determined by the maximum phonon energy of glass host and nanocrystals inside the glass host.In order to improve the up-conversion luminescence efficiency of glass-ceramics,researchers are constantly looking for lower phonon energy glass host and new types of lower phonon energy fluoride nanocrystals.However,the up-conversion luminescence of glass-ceramics is also affected by the local symmetry around the rare earth ions,and there is almost no relevant research report.Therefore,this paper improved the local structure symmetry around the rare earth ions by changing the composition of oxyfluoride glass-ceramics and controlling the precipitation of different types of fluoride nanocrystals,thereby improving the up-conversion luminescence efficiency of rare earth ions.?1?Ba₂LaF₇ grains incorporated in a smaller radius of Li⁺ions,were interstitial solid solution in which grains vary cubic lattice symmetry Ba₂La F₇ of Ho³⁺at a higher crystal symmetry in favor of the electron cloud the polarization enhancement layer 4f electron transitions but upconversion luminescence intensity increases.This provides an effective method for improving the conversion efficiency of the luminescent material.?2?This study changed the proportion of La F₃ and YF₃ in the glass composition.After heat treatment,the cubic phase Ba₂LaF₇ nanocrystals,intermediate phase nanocrystals and BaYF₅nanocrystals were precipitated in the glass host.In the process of nanocrystal structure transformation,the up-conversion luminescence intensity of the Tb³⁺ion in the intermediate phase nanocrystals is doubled compared with that of the cubic phase Ba₂La F₇ crystal.Through the in-depth study of the nanocrystal structure,the mechanism of enhancement of upconversion luminescence is finally given,which provides a new idea for improving the luminous efficiency of upconversion of materials.?3?In this study,Er³⁺-Yb³⁺ions were doped into the glass components of the previous section,which further explained the reason for the enhanced luminescence of the intermediate phase.In the process of crystal structure transformation,Er³⁺is more sensitive to the crystal field than Tb³⁺ions,the up-conversion emission color of Er³⁺ions can be regulated in different nanocrystal field environments,illustrated the change of the nanocrystal field environment around Er³⁺,and further studied on the mechanism of enhanced upconversion luminescence.