Research Of Eu Doping Effect On Phase,Microstructure And Optical Absorption Properties Of Nanocrystalline Rare-earth Hexaboride RB₆(R=Pr And Y)

The phase composition,microstructure and optical absorption of nanocrystalline multiple rare-earth hexaborides R_1-xEu_xB₆(R=Pr and Y)are investigated in present work.Experimentally,the single-phased nanocrystalline R_1-xEu_xB₆(R=Pr and Y)have been successfully prepared by the solid-state reaction,and their optical absorption properties was systematically measured.Theoretically,in order to explain the nature of optical absorption,the first-principle calculations are used to calculate the energy band,density of states and energy loss function of rare earth hexaborides to reveal the optical absorption mechanism.Finally,from the view point of practical application,the nanocrystalline Y_1-xEu_xB₆powder was mixed into organic polyvinyl butyral(PVB)to prepare the"heat insulating"glasses,which shows an excellent heat insulating effect.Therefore,this paper should be as an important reference and practical application value for expanding the optical applications of nanocrystalline rare earth hexaborides from both theoretical and experimental perspectives.The specific contents are as follows:1.Nanocrystalline Pr_1-xEu_xB₆was successfully prepared by the solid-state reaction of Pr Cl₃·7H₂O,Eu₂O₃and Na BH₄as raw materials at the reaction temperature of 1000?.The phase composition,crystal structure and optical absorption properties of multiple rare earth hexaborides were systematically studied.The characterization results of XRD,SEM and TEM show that all the prepared rare earth hexaboride powders have the CsCl-type cubic crystal structure.Elemental mapping results fully prove that Eu atoms have replaced the lattice positions of Pr atoms.The optical absorption measurement results show that the transmission wavelength wavelength increases from 618 nm to the near-infrared region of 1562 nm with the increase of Eu doping.First-principle calculations show that the redshifted of transmission wavelength is related to the plasmon resonance frequency energy and atomic valence states of Pr B₆and Eu B₆.As a result,the number of conduction electrons of Pr B₆is obviously reduced after Eu²⁺ions replace Pr³⁺ions,and the energy of the plasmon resonance frequency is also reduced.This leads to the corresponding transmission wavelength increases.2.In order to further study whether the YB₆has similar optical absorption properties with lanthanum hexaboride,the single-phased nanocrystalline YB₆were prepared by the solid-state reaction of YCl₃and Na BH₄and the Eu doping effect on the optical absorption properties of YB₆was systematically studied.in addition,a heat insulating film was prepared by combining the prepared powder with polyvinyl butyral(PVB),and the shielding ability of near-infrared light was studied.The results show that nanocrystalline Y_1-xEu_xB₆also has a Cs Cl-type cubic crystal structure.The optical absorption test shows that the wavelength of the transmitted light of YB₆increases from 839 nm to over 2500 nm with the increasing of Eu doping.The heat insulating measurements show that the ambient temperature of the blank film increases rapidly from 25?to 39.6?while prolonging the simulated solar light irradiation time.However,the ambient temperature increased from25?to 27.2?,27.8?,27.9?,31?and 28.7?for the Y_1-xEu_xB₆-PVB(x=0,0.2,0.4,0.6,0.8)films,indicating that they have a good heat insulating performances,which can be used in thermal insulation glass for automobiles and buildings.In addition,the superconducting properties of nanocrystalline YB₆is studied.The results show that when the transition temperature is T_c=2.75 K,the nanocrystalline YB₆transformed from the normal state to the superconducting state,the critical magnetic field is H_c2=0.18 T,and the electron-phonon interaction constant is?=0.63,which is less than 1.01of single crystal bulk YB₆.It is considered that the crystal defects such as lattice distortion and edge dislocation of nanocrystalline YB₆lead to the change of its phonon vibration frequency,thus reducing the electron-phonon interaction constant of nanocrystalline YB₆.In summary,the optical absorption properties of Pr_1-xEu_xB₆and Y_1-xEu_xB₆are investigated by the both of combination of theoretical calculation and the experimental measurements,which reveals the"red-shift"nature of the transmitted light wavelength for the first time.On the basis of above mentioned,the thermal insulation film prepared by the combination of nanocrystalline Y_1-xEu_xB₆and polyvinyl butyral(PVB),which shows excellent heat insulating properties.