The Preparation And Photoluminescence Properties Of The Alkaline-earth Metal Rare Earth Fluoride Doped With Ln³⁺ Ions

The rare earth ions have abundant electron energy levels because of its special 4f electron structure,and the number of transitions between energy levels is up to several hundred thousand.Thus,rare earth is a great treasure trove of optical materials,and more new luminescent materials will can be found.Rare-earth inorganic luminescent materials have many advantages such as excellent luminescence properties,sharp Stokes shift,long fluorescence lifetime,low toxicity,good chemical stability,and many others,making them more and more widely used in fields such as photoelectric conversion,lighting and display,and bio-imaging.Nowadays,rare earth oxides,phosphate,vanadate molybdate,carbonate,and other kind of fluoride compounds cause extensive research,compared with these of these compounds fluoride has a lower phonon energy(<500 cm^—1),which can reduce the non-radiative relaxation process and increase the conversion efficiency.Therefore,fluoride has been widely studied as a substrate for excellent up/down conversion of emission.In general,the chemical and physical properties of the micro/nano-structured functional inorganic materials are strongly influenced by the composition,phase,morphology and dimensions of the materials.High-temperature solid-state method,thermal decomposition method and hydrothermal method are the main methods for the synthesis of rare earth fluorides.Hydrothermal（solvent）method is a suitable method for simple operation,easy control,low reaction temperature and less environmental pollution.The main research contents of this paper are as following:（1）The Ba₃Sc₂F₁₂ micro/nanocrystals with controllable morphology were synthesized by one-step hydrothermal method with trisodium citrate(Cit^3-)as surfactant.The influences of surfactants,pH values,molar ratio of F^—/Sc³⁺and the concentration of Yb³⁺ions on the crystal phase,size and shape of final products have been studied in detail.We have found that the molar ratio of F^—/Sc³⁺and the concentration of Yb³⁺ions have a great influence on the aspect ratio of the crystal.We investigated the up-conversion spectra and luminescence mechanism of Ba₃Sc₂F₁₂:Yb³⁺,Ln³⁺（Ln=Er,Ho,Tm）crystals under 980nm excitation,and achieved multicolor in Ba₃Sc₂F₁₂:Yb³⁺,Ln³⁺（Ln=Er,Tm）systems.Luminescence up-conversion of white light emission in the Ba₃Sc_1.5856F₁₂:0.4 Yb³⁺,0.01Er³⁺,0.0044 Tm³⁺crystals was achieved at 980 nm with CIE coordinates of（0.274,0.287）.（2）BaLu₂F₈ crystals were synthesized via a one-step hydrothermal route without any surfactants.Used NaBF₄ as the fluorine source,the pure orthorhombic BaLu₂F₈ crystal can be precisely synthesized at pH=7.We discussed the influence of different fluorine sources and different pH values on the phase and morphology of the crystals.The doping of rare earth ions(Ln³⁺)with larger ionic radius and higher concentration of Yb³⁺ions can control the size and shape of the crystals.At the same times,different surfactants also affect crystal phase and morphology.The energy transfer process of Tb³⁺to Eu³⁺ions is discussed in BaLu₂F₈ crystals,and the multi-color emission of down/up-conversion is achieved in BaLu_1.94F₈:0.06 Ln³⁺（Ln=Sm,Eu,Tb,Dy,Er and Tm）crystals,BaLu₂F₈:Yb³⁺,Ln³⁺（Ln=Er and Tm）system and BaLu₂F₈:Yb³⁺,Ln³⁺（Ln=Ho,Tm）system.