Syntheses,Crystal Structures And Properties Of New Rare Earth Borate Luminescent Materials

White light LED（White Light Emitting Diode）has been intensively studied because of its advantages of low energy consumption,environmental protection,pollution-free and strong luminous brightness.However,development is limited due to a lack of red phosphors that can be efficiently excited by near-ultraviolet LED chips.As a result,research on high-efficiency red phosphors has always been a topic of great importance to people.In this paper,starting from exploring the synthesis of new rare earth borate luminescent materials,two new rare earth borate single crystals and their series of phosphors have been synthesized.Through single crystal and powder XRD,IR,Raman,UV-VIS and PL spectra,the relationship between their crystal structures and luminescence properties was studied.First,we prepared a new rare earth borate Cd₄Dy O（BO₃）₃ by a high temperature solution reaction at 950℃.The crystal structure data determined by single crystal XRD method are:space group Cm,a=7.9549（2）（?）,b=15.7792（3）（?）,c=3.4738（1）（?）,β=100.183（2）°,V=429.166（17）（?）~3,and Z=2.Its crystal structure is composed of one-dimensional[Dy O₄]_n^5n-chains formed by co-edge Dy O₆ octahedrons and one-dimensional[Cd₂O₆]_n^8n-double chains constructed by co-angular or co-edge Cd O₅ and Cd O₆ polyhedrons.Vibrational spectroscopy studies confirmed the presence of BO₃groups in the structure,the optical band gap was determined with the UV-vis absorption measurements,and the XPS spectroscopy confirms the chemical state of each element.Cd₄Dy_1-xSm_xO（BO₃）₃（0≤x≤0.8）phosphors were prepared by solid-phase reaction method,and its luminescence properties were studied.Under NUV excitation,by adjusting the concentration ratio of Sm³⁺/Dy³⁺,the luminous color of the Cd₄Dy_1-xSm_xO（BO₃）₃ phosphors can be changed from yellow-white to white and then to purple-white.The Cd₄Dy_0.8Sm_0.2O（BO₃）₃ phosphor excited at 364 nm has a CIE coordinate（0.338,0.328）and the calculated CCT value is 5240K,indicating that it can be used as a commercial single component white light emitting phosphor.Then,we prepared a new solid solution Bi_1.48Eu_0.52Pb_0.5Sr_0.5B₂O₇ by the high-temperature solution method at 850℃.The crystal structure data are:R（?）c,a=9.0085（2）（?）,c=38.8910（9）（?）,V=2733.26（13）（?）~3 and Z=18.It has a layered structure,in which alternate[BO₃]^3-triangles and[（Pb/Sr）O₆]^10-trigonal prisms are connected by a common O vertex to generate a two-dimensional layer,the[（Bi/Eu）₂O]⁴⁺group is located in the six-membered ring channel within the layer.The two layers connected by the （?）axis are stacked along the c axis to form a rhombic unit cell through the weak（Bi/Eu）-O bond.Vibrational spectroscopy confirmed the presence of the BO₃ group,the optical band gap was determined with the UV-vis absorption measurements,and the XPS spectroscopy confirms the chemical state of each element.In addition,the Bi_2-xPb_0.5Sr_0.5B₂O₇:x Eu³⁺（0.10≤x≤0.50）phosphors were synthesized by solid-phase reaction method,and its luminescence performance was studied.The emission spectra are composed of the spectral lines of ~5D₀→~7F_j（j=0,1,2,3）of Eu³⁺,and the optimal doping concentration of Eu³⁺ion is x=0.3.Under 394 nm excitation,the CIE coordinates of Bi_1.70Eu_0.30Pb_0.5Sr_0.5B₂O₇ phosphor are（0.640,0.359）,which matches to orange-red emission,indicating that the Bi_2-xPb_0.5Sr_0.5B₂O₇:x Eu³⁺phosphors can be potentially applied in lighting and display fields as orange-red phosphors.