Research On Morphology Control And Luminescence Mechanism Of Rare Earth Doped(oxy)fluorides Based Luminescent Materials

Rare-earth?RE?activated luminescent materials have been widely used in the fields of information,lighting,display,imaging,medical because of their turnable emission band,well-defined color purity,high absorption and emission efficiency,wide ranges of fluorescence lifetime originating from energy level transitions ofRE³⁺ions as well as good physical and chemical stabilities,exploration of novel and high efficient luminescent materials as well as controllable-adjustment of chemical compositions,morphologies and particle sizes of samples would become key scientific issues gradually with the development of inorganic luminescent materials.The first part of this dissertation is about synthesis the morphology-controllable and photo luminescence properties of Mn²⁺,RE³⁺co-doped?-NaYF₄?RE=Eu,Ce?via a facile hydrothermal route.NaYF₄ micro/nano-crystals with multiple morphologies,such as micro-rod,hexagonal nanoprisms and nanoplates have been prepared by adjusting the type of complexing agent,pH values and the concentration of transition metal Mn²⁺.It is found that trisodium citrate(Cit^3-)and pH values rather than Mn²⁺play important roles in fine-tuning the morphologies.In Mn²⁺,Eu³⁺-doped?-NaYF₄,the co-existence of Eu³⁺and Eu²⁺in?-NaYF₄has been discussed and demonstrated by XPS.Mn²⁺ions play a key role in the controlled emission of Eu³⁺/Eu²⁺co-doped NaYF₄.Broad band emission from the5d-4f transition of Eu²⁺and line emissions from 4f-4f transitions of Eu³⁺are observed in the mixed-valent Eu³⁺/Eu²⁺,Mn co-doped NaYF₄.In Mn²⁺,Ce³⁺-doped?-NaYF₄,with the increase of Mn²⁺content,the emission intensity of Ce³⁺gradually weakened,and the emission intensity of Mn²⁺gradually increased,and there was energy transfer between Ce³⁺and Mn²⁺,indicating that Ce³⁺could effectively enhance the orange green light emission of Mn²⁺.Oxyfluoride,which combines the structural properties of fluoride compounds and oxides,is a potential fluorescent matrix material and broaden the application field of fluorine-containing compound.The second part of this dissertation is about the uniform 1D microrods of RE³⁺doped Ln₇O₆F₉?Ln=Y and Lu;RE=Pr,Sm and Eu?,which were synthesized through a facile two-step hydrothermal method without extra fluorine source followed by post-heat treatment.The precursor composition was determined to be Ln?OH?_1.69F_1.31 using the Fourier transform infrared spectrum?FT-IR?,thermal gravimetric and differential scanning calorimetry?TG-DSC?.The average lengths of Y₇O₆F₉ and Lu₇O₆F₉ were about 6.8 and 7.9?m,respectively,with the average width of about 650 nm.It was interesting that the tip of the nano-rods exhibits a straight line and divergent umbrella shaped bifurcation for Y₇O₆F₉ and Lu₇O₆F₉,respectively.Upon ultraviolet excitation,Pr³⁺,Sm³⁺and Eu³⁺ions in Ln₇O₆F₉ showed blue,orange and red emissions originating from their characteristic f-f transitions.In addition,the 4f ¹5d¹?4f ² band emissions?340-450 nm?as well as typical 4f ²?4f ²line emissions?450-700 nm?of Pr³⁺were observed in Pr³⁺-doped Ln₇O₆F₉.For Sm³⁺-doped Ln₇O₆F₉,only the typical f-f transitions of Sm³⁺were observed with the absence of charge transfer?CT?band.However,a broad excitation band at 255 nm was observed in Eu³⁺-doped Ln₇O₆F₉ attributing to the charge transfer transition of Eu³⁺(i.e.O^2-?Eu³⁺CT).