Studies On Controllable Synthesis And Optical Properties Of Eu³⁺-Doped YF₃Crystals

In recent years, rare-earth fluoride micro-and nanoscale materials have receivedextensive attention due to their unusual properties and potential applications in solidlaser, integrated optic system, high-resolution displays, biological labeling, medicaldiagnosis, etc. It is well-known that rare-earth micro-and nanoscale materialsmorphology and structure have great influence on its luminescent properties.Therefore, developing controllable synthesis methods to micro-and nanoscale rare-earth phosphors, exploring their growth mechanism, in-depth studying the correlationbetween the morphology and optical properties, are crucial to the production ofmicro-and nanoscale rare-earth phosphors with designated. In this dissertation, thecontrollable synthesis，growth mechanisms and optical properties of micro-andnanoscale rare-earth phosphors were systematically investigated.In this dissertation, we report the controllable synthesis of YF₃:Eu³⁺microcrystals by a simple and environmental hydrothermal process by using somesimple inorganic salts as the “shape modifiers”. In addition, the phenomenologicalgrowth mechanisms for different shapes and the relationship between cationic andmorphology of products were also studied. The prepared samples were systematicallycharacterized by powder X-ray diffraction （XRD）, field emission-scanning electronmicroscopy （FE-SEM）, transmission electron microscopy （TEM）, photoluminescence（PL） and photoluminescent excitation spectra （PLE）. The main results aresummarized as follow: （1） A variety of microstructured YF₃:Eu³⁺with different morphologies had beensuccessfully synthesized by a simple and environmental hydrothermal process. Thesodium fluoride （NaF） was used as the fluoride source, the yttrium chloride （YCl₃）and the europium nitrate （Eu（NO₃）₃） were used to offer the yttrium and the europiumsource. Meanwhile, the adding different inorganic salts （AlCl₃,LiCl, MgCl₂·6H₂O,NaCl, KCl, BaCl₂） had a great impact on the morphology and structure of synthesisYF₃:Eu³⁺micro crystal material:（a） without any inorganic salt additive, the finalproducts were irregular and different polyhedral morphologies microparticle;（b）adding a certain amount of AlCl₃, the final products were uniform and regularwalnut-shape particles with a diameter of approximately400-500nm;（c） adding acertain amount of LiCl, MgCl₂·6H₂O or NaCl, the final products were manymicrobundles with an length of ca.500-600nm and a diameter of ca.100-200nm;（d）adding a certain amount of KCl or BaCl₂, the final products were truncated octahedralmicrostructure with an average length of ca.4ｕm. The results of the XRD analysisshow that all shapes of YF₃: Eu³⁺were pure orthogonal crystal system. We believethat this approach might be applied to the synthesis of a new generation of importantfluorides, even complex fluoride micro-or nanomaterials. In addition, we studiedsystematically the effects of inorganic salts （especially among the cations） onYF₃:Eu³⁺microcrystal structure, scale and morphology, while other reactionconditions were kept constant.（2） Based on the synthesized YF₃: Eu³⁺with different morphologies, reactionproducts with different growth stages were carefully examined by FE-SEMobservations. Detailed proofs indicated that the process of different morphologiesYF₃:Eu³⁺microparticles growths were dominated by different growth mechanisms:（a）the nucleation–crystallization–self-assembly growth process is obvious evolutionstages for the synthesis of the YF₃:Eu³⁺with walnut-like shape;（b） thecrystallization–dissolution–recrystallization–self-assembly growth process is obviousevolution stages for the synthesis of YF₃:Eu³⁺microbundles;（c） thenucleation–crystallization growth process contains obvious evolution stages for thesynthesis of truncated octahedral YF₃:Eu³⁺microcrystals. In addition, TEM showed their crystallinity and single polycrystalline.（3） The excitation and emission spectra of YF₃:Eu³⁺microcrystals with differentmorphologies were discussed. Our results reveal that although the positions of themajor peaks in the excitation and emission spectra were identical in these samples,their intensities were different. The difference in luminescent intensity of YF₃:Eu³⁺microcrystals with different morphologies can be ascribed to the combined roles oftheir various dimensions, morphology, and the degree of crystallinity.