Fabrication And Luminescent Properties Of Eu³⁺-Doped NaYF₄Phosphors

Rare earth doped NaYF4nanocrystals, which have two polymorphic forms:cubic (-) NaYF4and hexagonal (-) NaYF4, have received intensive attention inrecent years because of their unique luminescence properties as a result of their verylow phonon energy. However, their luminescence is largely limited by the low opticalabsorption of rare earth ions, and because of this, an extensive amount of attentionhas been focused on the modification of RE-doped luminescent phosphors.In this paper, the influences of experimental conditions to synthesize-NaYF4microcrystals through molten-salt method are systemically studied. Under the optimalprocess, keeping the molar ratio of Y3+/F-=1:32, carrying out for120min under350oC, then cooling down to the room temperature during1h,-NaYF4: Eu3+microrodshave been synthesized with different Eu3+concentration. At the same time, theluminescence characteristics of Eu3+doped-NaYF4microrods have been studiedand the quenching concentration has been identified.In addition, this paper presents a novel strategy to prepare highly dispersible andstrongly luminescent Eu3+doped-NaYF4: Eu3+nanocrystals, which can beintensively excited via multi-channel optical absorption. Highly dispersible-NaYF4:Eu3+nanocrystals, with the average size about28nm, are synthesized using asolvothermal method, and they are coated with a SiO2layer to form the-NaYF4:Eu3+@SiO2core-shell nanostructures. These-NaYF4: Eu3+@SiO2core-shellnanostructures are thermally annealed and the SiO2shell is then removed to obtainthe annealed-NaYF4: Eu3+nanocrystals with strong O2-→Eu3+charge transferexcitation beyond that the nano-size control of annealed crystals is successfullyachieved. Luminescence of the-NaYF4: Eu3+nanocrystals is further enhanced byenergy transfer of organic ligands PMA and BA after forming a types ofinorganic-organic hybrid nanostructure. This strategy, which is firstly introduced byus, is also useful for developing other type of dispersible and strongly luminescenceand multi-channel excitation nanocrystals.