Controlled Synthesis,Optical Properties And Applications Of Lanthanide-Doped Inorganic Nanocrystals

In this thesis,lanthanide(Ln³⁺)-doped inorganic luminescent nanomaterials including ultrasmall scandium oxide,lithium zirconium fluoride and sodium zirconium fluoride nanocrystals?NCs?are treated as the object of study.Based on the controllable synthesis of these NCs,by utilizing surface modification,structure exploring and local structure engineering with the combination of high resolution photoluminescence?PL?spectra,temperature-dependent upconversion?UC?luminescence?UCL?spectra and first-principle calculations,we have facilitated the resolution of some essential scientific issues such as low PL emission efficiency in ultrasmall Ln³⁺-doped oxide NCs and unclear luminescent mechanism of the local-structure-dependent UCL of Er³⁺ions in Ln³⁺-doped inorganic upconversion nanocrystals?UCNCs?,etc.The applications for these nanomaterials were preliminarily explored in some fields like fluorescence bioassay and fluorescence nanothermometer,etc.The research results are briefly summarized as follows:?1?Utilizing high-temperature thermal decomposition method,we demonstrate for the first time the fine tuning of the size of Sc₂O₃:Eu NCs within an extremely small nanometer scale from 2.6 to 9.7 nm.Moreover,we develop an effective strategy to fundamentally circumvent the notorious disadvantage of weak luminescence of ultrasmall NCs.In our design,2-naphthoyltrifluoroacetone??-NTA?was noncovalently incorporated into the hydrophobic cavity formed by the two hydrophobic tails of amphiphilic phospholipids(DSPE-PEG₂₀₀₀)and oleic acid?OA?capped on the nanocrystal surface,and then used as the energy donor to transfer its excitation energy to adjacent Eu³⁺ions located at the surface of ultrasmall Sc₂O₃:Eu NCs,thereby giving rise to intense red emission of Eu³⁺.Furthermore,research showed that the size of Sc₂O₃:Eu NCs is smaller,enhanced luminescence is higher.?2?Utilizing high-temperature co-precipitation method,we have successfully prepared two kinds of Yb³⁺/Er³⁺co-doped lithium zirconium fluorides possessing identical elemental compositions but different stoichiometric ratios by easily tuning the amount of reactants,including Li₄ZrF₈:Yb/Er and Li₂ZrF₆:Yb/Er UCNCs.Through TEM and nitrogen adsorption test under 77 K,Li₄ZrF₈:Yb/Er UCNCs were demonstrated to be a kind·of novel porous structural inorganic luminescent material,while Li₂ZrF₆:Yb/Er UCNCs were solid structural ones.Compared with solid structural UCNCs,abnormal UCL was observed in porous Li₄ZrF₈:Yb/Er UCNCs.Given this,we considered Li₄ZrF₈:Yb/Er UCNCs as an UC fluorescence nanothermometer,and temperature-dependent UCL measurements showed a good linear fitting result over a wide temperature range of 10-623 K and the sensitivity was comparable to the reported upconversion fluorescence thermometers.?3?By virtue of high-temperature co-precipitation method,we have successfully synthesized three kinds of Yb³⁺/Er³⁺co-doped sodium zirconium fluorides possessing identical elemental compositions but different stoichiometric ratios by easily tuning the amount and kind of reactants,including Na₃ZrF₇:Yb/Er,Na₅Zr₂F₁₃:Yb/Er and Na₇Zr₆F₃₁:Yb/Er UCNCs.Spectroscopic study shows that UCL red-to-green?R/G?ratios increase with the rising of local crystal structure symmetries.In combination with the first-principle calculations based on density functional theory?DFT?,we show that such local-structure-dependent UCL of Er³⁺ions is primarily due to varied electronic band structures induced by the Yb³⁺/Er³⁺doping in different crystallographic structures.After corroborating the possibility and generality to manipulate the UCL through engineering the local structure in diverse Ln³⁺-doped UCNCs,we have drawn a conclusion,that is,the higher symmetry of crystal structure of host,the larger UCL R/G ratio of the doping Er³⁺ion in Ln³⁺-doped inorganic UCNCs.