Design,Synthesis,Optical Properties And Crystal Growth Mechanism Exploration Of Rare Earth Upconversion Nanoparticles

Lanthanide ion doped upconversion nanoparticles,enabling two or more low energy photons to transform into higher energy photons,recently emerge as a new type of luminescent nanomaterials.The unique optical properties of upconversion nanoparticles,including high photo stability,low background,fingerprint emission and tunable luminescent lifetime,make them promising candidates for sensing,anti-counterfeiting,and bioimaging.As a recently prevalent topic,the unique properties of Sc-based nanomaterials,such as different luminescence upconversion behavior from those of Y-based nanocrystals,have few reports.In addition,comprehensive investigations on the precise synthesis,phase transition details,and especially the fascinating upconversion luminescent properties of ScFx:Ln nanocrystal series,are still empty.Herein,we explore the crystal growth process,phase transformation mechanism and upconversion luminescence properties in detail.Furthermore,we investigate the effect of doping on the cubic ScF3 nanocrystal growth process.What is more,we develop a one-for-all synthesis recipe,which allows the successful synthesis of each REF3 nanocrystals in a controlled manner.This thesis can be divided into four sections.1.ScFx:Ln(x = 2.76,3):Controlled Synthesis and Crystal Growth Mechanism ExplorationIn this work,we demonstrate the synthesis of ScFx upconversion nanoparticle by thermal coprecipitation method and gain deep insight into the formation process.By changing the reaction temperature,we can obtain three types of scandium fluoride nanoparticles,which are tetragonal ScF2.76,orthorhombic ScF3 and cubic ScF3.With further monitoring of the nanoparticle formation process,we find that.under our experimental conditions,both tetragonal ScF2.76 and orthorhombic ScF3 nanorods can be obtained through the growth of small nanoparticles.In stark contrast,cubic ScF3 upconversion nanoparticles are formed by the dissolution of orthorhombic ScF3 and a sequential recrystallization.Furthermore,these efforts may also shed light on the development of Sc based multifunctional nanomaterials.2.The Upconversion Photoluminescence Properties Exploration of ScFx:Ln(x = 2.76,3)NanocrstalsIn this work,we investigate the upconversion photoluminescence properties of ScFx:Yb/Er nanocrystals at tetragonal,orthorhombic,and cubic phases.They all produce strong green upconversion emission where cubic nanocrystals show the strongest luminescence,orthorhombic ones are at the medium level,and tetragonal nanocrystals give the weakest.Except the strong green and blue upconversion emission generated by ScF3:Yb/Ho(30/2,mol%)and ScF3:Yb/Tm(30/0.5,mol%),respectively,variation of the co-doping concentration of Yb3+/Ho3+ and Yb3+/Tm3+ can further create a rich library of upconversion emission codes with pre-defined luminescence intensities that may potentially be used for luminescent code-based gene and/or disease multiplexing,especially when combined with the results of optical images of the samples discussed above,confirming the wide-range upconversion emission capability and fine-tunability of cubic ScF3 nanocrystals,which is rarely seen in a single-host material among previous upconversion studies.To further prove the high quality of the host material,?20 nm cubic ScF3:Yb/Tm(30/8,mol%)nanocrystals were used for single-particle upconversion luminescence study,which suggests the high quality and uniformity of cubic ScF3 nanocrystals as host materials.Our upconversion luminescence studies of these nanoparticles indicate that ScF3 nanoparticles should have potential applications in photoluminescence areas,emission display and biolabeling.3.Doping-Facilitated Growth of Rare Earth-Based NanocrystalsIn this work,we investigate the effect of doping on the crystal growth process of Rare Earth-Based Nanocrystals.Our experimental results have shown that except the luminescence/enhancement capability,the dopant ions including both lanthanide ions and lithium ions,can facilitate the growth of the nanocrystals,which has never been reported before.In terms of greatly reduce the reaction temperature,or shorten the reaction time,which have imparted us more flexibility for nanocrystals synthesis that are previously impossible and have also paved a new direction for nanocrystals design and synthesis with multifunctionalities.We believe this discovery shall be a general principle that will also work for the nanocrystals rather than rare earth-based ones,which is an ongoing project in our lab.4.Insights into the Growth Principles of REF3(RE = La-Lu,Y)Nanocrystals:Hexagonal and/or OrthorhombicIt has remained an open challenge in synthesizing REF3(RE = La-Lu,Y)nanocrystals with expected phase structures.In this work,we have developed a one-for-all synthesis recipe,which allows the successful synthesis of each REF3 nanocrystals in a controlled manner.Experimental results have shown that the radius of RE ions determines the phase structure where pure hexagonal REF3(RE = La-Eu),the mixture of hexagonal and orthorhombic REF3(RE = Gd),and pure orthorhombic REF3(RE = Tb-Lu,Y)nanocrystals are obtained respectively,upon the decreasing of the ionic radius.As Gd sits exactly in the middle of the lanthanide element row,GdF3 nanocrystals were used as a representative to further showcase how the molar ratio of F-:Gd3+,the doping of RE ions with different ionic radius,and the doping concentration of certain RE ions will affect the crystal structure of the final product.