Preparation And Luminescent Properties Of Rare-earth Eu²⁺ Doped Ca_2-2xM（Sr,Ba）_2xMgSiO₂O₇

Rare-earth doped luminescent materials with excellent luminescent properties havebeen widely used in display, lighting, high-energy particle detection and recording,optoelectronic communications, agriculture and military fields. When Eu²⁺ions aredoped in a crystal, they exhibit characteristic wide5dâ†'4f emission band. Therefore, theluminescence color can be tuned by different substrates from ultraviolet to infrared;fluorescence lifetime is short.Silicate-based phosphors, with good chemical stability and high luminescence，have developed to be a kind of very important photo-luminescent materials. The radiusof Eu²⁺, Ca²⁺, Sr²⁺and Ba²⁺is0.112nm,0.099nm,0.112nm and0.134nm respectively.The similarity of the radii between alkaline metal ions and Eu²⁺ions makes it easy forEu²⁺to enter the host lattice without disturbing the crystal stability. Different emissionwavelength can be tuned by substituting different alkaline-earth metals and dopingconcentration. So, different emission wavelength and different color can be got.In this paper, Eu²⁺doped Sr₂MgSi₂O₇phosphors were synthesized and impacts ofcations on structure and luminescent properties were also studied by substituting Ca²⁺with Sr²⁺and Ba²⁺; meanwhile Ca₂MgSi₂O₇:Eu²⁺fibers were also synthesized by asol-gel assisted electro-spinning method and luminescent properties of the fibers werediscussed.In chapter three, Eu²⁺-doped Sr₂MgSi₂O₇phosphors were synthesized by hightemperature solid sintering method. XRD results show that the doping does not affectthe structure, without a slight difference in crystal lattice. The excitation spectrum has avery broad absorption from225-425nm, which agrees with the emission light of nearUV-LED chips. The luminescence intensity reaches the maximum when the dopingconcentration becomes5%. Lifetime is calculated through decay curves. From thechromaticity coordinate graph, it is found that Eu²⁺-doped Sr₂MgSi₂O₇phosphors emitlights within blue zone and chromaticity coordinates do not change much with the increasing doping concentration.In chapter four, Ca_1.94-2xFu_0.06MgSi₂O₇（x=0,0.17,0.37,0.57,0.77,0.97）phosphors were synthesized by high temperature solid state method. XRD analysisshows that all the diffraction peaks shift to smaller angles upon increasing the Sr²⁺.Crystal plane spacing d becomes bigger and unit cell volume is larger. A blue shift,from539to470nm, was found in the emission spectra. The emission intensity increasedwith increased Sr²⁺-doping and reached a maximum when the Ca²⁺was completelysubstituted by Sr²⁺. All the wide emission band correspond to4f65d1â†'4f7（8S7/2）transition of Eu²⁺. Chromaticity coordinates diagram shows that when the dopingconcentration increases, luminous color changes from yellow-green（0.303,0.550）) toyellow（0.194,0.433） and then to blue （0.132,0.174） color, respectively to achievetunable luminescent color.In chapter five, a series of Ca_1.94-2xFu_0.06MgSi₂O₇（x=0,0.07,0.17,0.27,0.37,0.47,0.67,0.77,0.87） phosphors were synthesized and the impacts of substituting Ca²⁺with Ba²⁺on structure and luminescent properties are explored. As the concentrationincreases, the structure of the phosphor changes from P21m to P. The luminescentcolor changes from yellow-green（0.303,0.550） to blue（0.139,0.118）. The emissionintensity first decreased to a minimum and then slightly reached a maximum.In the sixth chapter, Ca₂MgSi₂O₇:Eu²⁺luminescent fibers were synthesized by asol-gel assisted electro-spinning method. The average diameters of luminescent fibersranged from0.6to0.9μm. Due to thermal grooving, the diametric distribution along theaxial direction of single fibers is relatively homologous. Ca₂MgSi₂O₇:Eu²⁺fibers havealmost two times higher emission intensity than the powder sample prepared by hightemperature solid state reaction. The calcination temperature of the fibers was decreasedto1150°C, which is beneficial to energy saving and defects reducing. The broadexcitation band, extending from250nm to500nm, implies that this Ca₂MgSi₂O₇: Eu²⁺fiber phosphor can be well excited by near UV light, which well matches the UV-LEDchips （360-400nm） and blue LED （450nm）.The novelities of this dissertation are the following: it is the first time to synthesizeCa₂MgSi₂O₇:Eu²⁺luminescent fibers by a sol-gel assisted electro-spinning method. Theresults show that this phosphor can be excited by near ultraviolet light, which matcheswell with UV-LED and blue LED chips, and it is promising in white LED phosphor applications. The study of Sr²⁺, Ba²⁺substituting Ba²⁺in the Eu²⁺-doped phosphorsshows that the color tuneable phosphors from green to blue can be synthesized.