Spectroscopic Study On Lanthanide-doped KGd₂F₇ Nanocrystals

Trivalent Lanthanide(Ln³⁺)-doped fluoride nanocrystals（NCs）in the category of ALn₂F₇（A=Li,Na,and K）have recently emerged as a potential alternative to the well-developed ALnF₄-type fluorides for the generation of novel luminescence of Ln³⁺owing to their unique crystallographic structures.In this thesis,we studied the controlled synthesis of monodisperse Ln³⁺-doped monoclinic-phase KGd₂F₇ NCs via a facile thermal decomposition method.Characteristic downshifting and upconverting luminescence（UCL）of Ln³⁺ion ranging from the visible to near infrared spectral regions were readily tuned in the KGd₂F₇ NCs after doping with different Ln³⁺emitters.By utilizing Eu³⁺ion as a structural probe,the local crystal structure of Ln³⁺ion in the KGd₂F₇ NCs was investigated in detail based on the high-resolution photoluminescence spectra at low temperature（10 K）.Moreover,we have aslo fabricated a series of KGd₂F₇:Yb/Er core/shell NCs with different architectures of inert KGd₂F₇ and active KGd₂F₇:Yb shells,which thereby allowed us to carry out a comparative spectroscopic investigation of the optimum core/shell architecture for highly enhanced UCL of Ln³⁺.Specifically,the KGd₂F₇:Yb/Er core/shell NCs with optimized thickness of inert KGd₂F₇shell were found to outperform their counterparts with active KGd₂F₇:Yb shell in terms of UCL intensity and lifetime,and thus validating our finding that the inert epitaxial shell growth around the optically active core-only NCs was the optimum core/shell design strategy to minimize the surface quenching effect.These results would unambiguously provide new fundamental insights into the rational design of complicated core/shell nanostructures with highly enhanced UCL of Ln³⁺,and would further push forward the development of novel luminescent nano-materials based on Ln³⁺-doped KGd₂F₇ NCs for versatile applications.