Syntheses,Crystal Structures And Properties Of New Eu-containing Borate Luminescent Materials

White Light Emitting Diode(W-LED)has been widely concerned and studied for its advantages such as energy saving,environmental protection and high light emission.However,the lack of efficient red phosphors that can be effectively excited by ultraviolet/near-ultraviolet LED chips limits the development of white LED,so it is very important to explore the synthesis of new red phosphors.Eu³⁺ion has a long fluorescence life,high color purity,and little external influence,it is an indispensable rare-earth ion for the preparation of red phosphors.In this paper,single crystals and phosphors of three new rare-earth borates were synthesized based on the exploration of novel Eu-containing borate luminescent materials.The crystal structure and phase purity were determined by single crystal and powder XRD,and the anionic groups present in the crystal and the luminescent properties of the phosphors were studied by infrared and Raman spectra,UV-Vis diffuse reflectance spectra and fluorescence spectra.In addition,the electronic structures of the two representative compounds were also calculated.First,a new europium borate Eu Cd₃(Al O)₃(BO₃)₄ has been prepared by the high-temperature solution reaction at 850°C and structurally characterized by single crystal XRD analyses.It belongs to gaudefroyite type of structure,crystallizing in the polar hexagonal space group P6₃ with a=10.390(2)?,c=5.7244(14)??V=535.2(2)?³?Z=2.Its structure features a three-dimensional framework composed of 1D[Al O₄]_n^5n-chains that are bridged by BO₃ triangles,with small channels accommodating Eu³⁺/Cd²⁺ions only and big channels hosting Eu³⁺/Cd²⁺ions together with BO₃ groups.The existence of BO₃ groups was confirmed by vibrational spectroscopy.The photoluminescence of Eu Cd₃(Al O)₃(BO₃)₄ was studied.The emission spectra consist of groups of peaks in the red and orange spectral region due to ⁵D₀?⁷F_J(J=1,2,3,4)electronic transitions of Eu³⁺ions and the decay curves show the biexponential behavior.Moreover,band electronic structure has also been investigated.Secondly,two alkali-earth and rare-earth metal borates,M₃Eu₂(BO₃)₄(M=Ba,Sr),have been synthesized and their crystal structures determined by single-crystal XRD methods with the following crystal data:Ba₃Eu₂(BO₃)₄(1),Pnma,a=7.6970(15)?,b=16.554(3)?,c=8.9300(18)?,V=1137.8(4)?³,Z=4;Sr₃Eu₂(BO₃)₄(2),Pnma,a=22.2553(4)?,b=15.9122(3)?,c=8.7568(2)?,V=3101.05(11)?³,Z=12.The compound 1 is isotypic with Ba₃RE₂(BO₃)₄(RE=Y,La,Pr,Nd)and its crystal structure features a 3D framework constructed by BO₃ triangles and 8-fold coordinated positions M1,M2 and M3 with mixed Eu/Ba occupation.2 adopts a threefold superstructure of the structure of 1.IR and Raman spectra further confirm that both 1 and 2 contain the planar triangular BO₃ groups.The photoluminescence spectra of 1 and 2 consist of five groups of emission bands assigned to the ⁵D₀?⁷F_J(J=0,1,2,3,4)transitions within Eu³⁺ions and the decay curves show the single-exponential behavior with the lifetime being 1.358 and 0.887ms for 1 and 2,respectively.1 possess a very high luminescent efficiency(QE=90.09%)which benefited to being applied in warm white LEDs.Moreover,X-ray photoelectron spectroscopy(XPS)is used to analyze the chemical states of the elements and the band electronic structure on 1 has also been investigated.The quantum efficiency of the above three phosphors are higher than that of commercial red phosphor Y₂O₂S:Eu³⁺(QE=35%,?_ex=317 nm),and can be effectively excited by ultraviolet/near-ultraviolet,indicating that they have potential applications value.