Preparation And Performance Study Of Rare Earth Nano-fluoride

Colloidal NaLuF₄:Ln³⁺?Ln=Yb/Er,Yb/Gd/Tm and Gd/Eu?nanocrystals were synthesized by a hydrothermal method.The effects of NaF/Ln?NO₃?₃ ratio on the phase compositions,morphologies and luminescence properties of NaLuF₄:Ln³⁺nanocrystals were investigated in detail.The results indicated that larger NaF/Ln?NO₃?₃ ratio is benefit for the formation of hexagonal phase NaLuF₄:Ln³⁺.Multicolor up-conversion luminescence tuning of NaLu F₄:Ln³⁺nanocrystals was successfully achieved by adjusting lanthanide-ion-doped content.Especially,the ⁶P_7/2?⁸S_7/2/2 transition from Gd³⁺ions was observed in NaLu F₄:Yb³⁺/Gd³⁺/Tm³⁺nanorods under 980 nm excitation.Decay dynamics was performed to study the down-conversion luminescence properties of the NaLu F₄:Gd³⁺/Eu³⁺nanorods.All the decay curves can be well fitted with a second order exponential decay function.Ln³⁺doped NaYF₄/Y₂Ti₂O₇/TiO₂ microfibers were prepared by combining the hydrothermal method with electrospinning technique.And then,Ln³⁺doped NaYF₄/Y₂Ti₂O₇/TiO₂/Bi₂MoO₆ hierarchical structures were prepared by growing Bi₂MoO₆:Er³⁺nanoparticles on the surface of NaYF₄/Y₂Ti₂O₇/TiO₂ microfibers.Tunable upconversion luminescence was successfully achieved by adjusting the Ti O₂ and Bi₂MoO₆:Er³⁺contents.The mechanism of upconversion luminescence was investigated in detail.The results indicatedthat two-and three-photon processes are responsible for populating the ⁴S_3/2/²H_11/21/2 levels in Ln³⁺doped NaYF₄/Y₂Ti₂O₇/Ti O₂ and NaYF₄/Y₂Ti₂O₇/TiO₂/Bi₂MoO₆,respectively.The BET surface areas of Ln³⁺doped NaYF₄/Y₂Ti₂O₇/TiO₂/Bi₂MoO₆ increased with the Bi₂MoO₆:Er³⁺content increasing.In addition,the photocatalytic activity of Ln³⁺doped NaYF₄/Y₂Ti₂O₇/TiO₂ and NaYF₄/Y₂Ti₂O₇/TiO₂/Bi₂MoO₆ was evaluated by the degradation of rhodamine B aqueous solution under ultraviolet and visible light irradiation.MTiO₃?M=Ca,Ni and Zn?nanocrystals were prepared via a facile ethylene glycol-mediated synthesis route followed by calcination in air.The structures and morphologies of nanocrystals were characterized by x-ray diffraction,Raman spectroscopy,transmission electron microscopy,and scanning electron microscopy.The results indicated that CaTiO₃ and NiTiO₃ are orthorhombic phase,while the ZnTiO₃ is orthorhombic phase.The activity of the CaTiO₃ nanocrystals for water splitting into H₂was obviously higher than those of the NiTiO₃ and ZnTiO₃ nanocrystals,which could be attributed to the more negative conduction band position of CaTiO₃ than NiTiO₃ and ZnTiO₃.The Brunauer–Emmett–Teller system-based surface areas of samples are 19.03,21.13 and 4.17m²/g for CaTiO₃,NiTi O₃ and ZnTi O₃ nanocrystals,respectively.In addition,the activity of the CaTiO₃ nanocrystals increased with increase in the sintering temperature of samples.