Preparation,Characterization And Optical Absorption Properties Of Nanocrystalline Multiple Rare-earth Hexaborides Sm_1-xEu_xB₆

Due to the surface plasmon resonance（SPR）effect,the nanocrystalline binary rare-earth hexaboride（RB₆）exhibits the characteristics of strong near-infrared light absorption and high visible light transmission.The optical properties not only meet the needs of manufacturing thermal insulation glass in industry,but also can kill some cancer cells by absorbing near-infrared light and releasing heat in medicine effectively.Therefore,the research on the optical properties of nano rare-earth hexaboride has become a hot spot.However,the research on this system is mainly focused on nano LaB₆,and there are few reports on the light absorption of other rare-earth hexaborides,especially on the preparation and optical absorption of multi rare-earth hexaborides at present.As we all know,SmB₆ is not only a new generation of topological insulating material,but also an ideal thermal cathode material.But its optical properties are rarely reported.Therefore,the preparation,characterization and optical absorption properties of Sm_1-xEu_xb₆ nanocrystalline were studied.The main contents of this paper are composed of following:（1）The preparation of SmB₆nanocrystalline by evaporative condensation method and the study of optical absorption.The spherical nanocrystalline with an average grain size of 50 nm was successfully prepared by evaporation condensation method with the polycrystalline rod of SmB₆ as the precursor.However,it is difficult to control the grain size and morphology of the nanocrystalline prepared by this method,which makes it difficult to study the optical absorption properties of the rare earth hexaboride.（2）In order to solve these problems,the solid-state reaction method was used to prepare the nano-sized SmB₆ powder with controllable grain size and morphology.The main method is to use SmCl₃·6H₂O and NaBH₄ as the source of rare earth and boron,and control the reaction temperature between 800-1150℃in vacuum environment,so as to realize the controllable technology of grain size and morphology.It was characterized by XRD,SEM and TEM.（3）On the basis of the above solid-state reaction method,this section focuses on the preparation and optical absorption properties of the multiple rare-earth hexaborides Sm_1-xEu_xB₆ nanocrystalline.The effect of Eu doping on the phase,crystal structure and optical absorption of nanocrystalline SmB₆ is discussed.The results of XRD and SEM show that the multiple rare-earth hexaboride is a single-phase,cubic nanocrystalline with an average grain size of 50 nm.The mapping results of single particle element in TEM show that the doping atom Eu replaces the lattice position of Sm atom.The results of optical absorption measurement show that when the Eu doping amount is x=0.1,0.2,0.3,0.4,0.6,0.8,the transmission wavelength positions of nanocrystalline SmB₆ are 705 nm,734 nm,756 nm,843 nm,892 nm and 1000 nm,respectively.It shows that the transmission wavelength of nanocrystalline SmB₆ is‘red shifted’with the increase of Eu doping amount.The new performance will be used to expand its optical application.In order to reveal the influence mechanism of Eu doping on the transmission wavelength of nanocrystalline SmB₆ theoretically,a 2×2×2supercell model with 12.5%(Sm_0.875Eu_0.125B₆)doping was constructed by using the first principle of density functional theory,and the band structure,density of state and energy loss function were calculated.The results show that the Eu-4f electronic state of the doped element has a strong hybridization phenomenon near the SmB₆ Fermi surface.The results of energy loss function show that the incorporation of Eu atoms reduces the resonant frequency energy of SmB₆ plasma from 1.49 eV to 1.25 eV,which also qualitatively explains the red shift of transmission light wavelength corresponding to this energy.In addition,from the experimental point of view,the influence of reaction temperature on the optical absorption properties of the rare earth hexaboride was discussed.The results show that the‘blue shift’occurs with the increase of reaction temperature.（4）Finally,in order to explore whether the nanocrystalline SmB₆ can be used as an activator in the BaNb₂O₆ matrix material,the prepared nanocrystalline SmB₆ was doped by the solid-state reaction method,and the luminescent properties were compared with that of the Sm₂O₃ doped.The results of XRD and SEM show that the main phase of Ba_1-xNb₂O₆:xSmB₆ powder is of the structure of BaNb₂O₆,the particle size of the powder is micron sized,and there are some impurity phases of SmBO₃.The results show that the excitation wavelength isλ_ex⁴07 nm and the emission wavelength isλ_em⁵63 nm.When the doping amount of nanocrystalline SmB₆ is x=0.03,the luminescent intensity is 4 times of that of the sample doped with Sm₂O₃.The results show that nanocrystalline SmB₆has good photoluminescence properties in the BaNb₂O₆ matrix materials.In conclusion,the nanocrystalline multiple rare-earth hexaboride Sm_1-xEu_xb₆ not only has good optical absorption properties,but also the transmission wavelength is linearly adjustable with the increase of Eu doping.At the same time,this paper also found that nanocrystalline SmB₆ as an activator has good luminescent properties in niobate matrix.Therefore,nanocrystalline Sm_1-xEu_xB₆ as a multifunctional material will have a wide optical application prospect.