Synthesis Of Upconversion Nanocrystals And Research On Broadband Sensitization

Upconversion luminescence materials have significant advantages such as unique anti-stokes luminescence,low autofluorescence background and low photobleaching.So upconversion luminescence materials have attracted extensive attention owing to their potential applications in a large variety of fields,for example,bioimaging,three-dimensional display,photodynamic therapy,anti-counterfeiting encryption and solar photovoltaic.However,commercial applications of upconversion materials need to be further studied.This thesis will conduct targeted research on the basis of systhesis of upconversion nanocrystals and broadband sensitization of upconversion phosphors,the major achievements are as follows:NaYF₄:Yb³⁺,Er³⁺upconversion nanocrystals were prepared by coprecipitation method.The effects of different sodium source,different morphology of Na F,different adding methods and different morphology of solid NH₄F on the crystal phase,size and morphology of the upconversion nanocrystals were studied.The experimental result shows that using different sodium source regulates the morphology of Na F in the whole reaction system indirectly.As an intermediate,the reactivity of Na F varies with size and morphology.Synthesis of?phase upconversion nanocrystals is hard if reactivity of Na F is low.Using“Na/F source separation method”can realize competitive mechanism of“formation of Na F”and“nucleation of?phase”and minimize the advance formation of Na F.Researching different morphology of solid NH₄F is similar to the study of Na F.Various morphologies of NH₄F have different reactivities.Regulating morphology of NH₄F will change its ability to release monomer into the reaction system and influence the final size of upconversion nanocrystals.Based on NaYF₄:Yb³⁺,Er³⁺upconversion nanocrystals,the 7.5 nm ultra-small upconversion nanocrystals were synthesized by tuning other process parameters in“Na/F source separation method”.The growth processes of upconversion nanocrystals at high temperature using different methods were studied.The reason why the sizes of upconversion nanocrystals are reduced was analysed by classical nucleation theory:the initial?phase with poor crystallinity is more favorable to increase the?phase nucleation rate.Thus,ultra-small nanocrystals can be synthesized.The novel Cr³⁺broadband sensitized upconversion phosphor Li Sc Si₂O₆:Cr³⁺/Er³⁺was designed and synthesized successfully.The experimental result shows that Li Sc Si₂O₆:Cr³⁺/Er³⁺had wideband absorbtion by 600 nm?800 nm.And upconversion luminescence of Er³⁺sensitized by Cr³⁺upon excitation at 690 nm can be realized.The broadband upconversion mechanism of Li Sc Si₂O₆phosphor was explained by fluorescence spectrum analyses.The effects of doping concentrations of Cr³⁺,Er³⁺and Yb³⁺on upconversion luminescence were also investigated.