| Nowadays,global energy consumption for lighting is becoming higher and higher.White light-emitting diodes(w-LEDs)have attracted increasing attention and considered to be the next generation energy-saving lighting systems because of their advantages such as high efficiency,low power consumption,and long lifetime.Currently,the main strategy of producing w-LEDs is combing blue chips with yellow emitting YAG:Ce3+ phosphors,but with lower color index,higher color temperature,and thermal stability in need for improvement.Therefore,it is not recommended to use in high power equipment for long term.In order to meet the requirements of high-power LED applications,researchers have attempted to produce high-quality w-LEDs based on the three-color mixture principle.At present,the biggest problem is how to prepare red and green phosphors with high thermal stability,to realize better color index and lower color temperature of w-LEDs.On the other hand,compare to rare earth ions,transition metal Mn2+ is a potential active ion to replace the rare earth ions for its low costs,wider range of spectra and sensitive to strength and symmetry of the crystal field.Meantime,the Mn2+ ion can also become impurity sensitizing agent to improve the luminescence of phosphor.From the mentioned above,in the present research,Mn2+ ions have been selected and doped in the SiAlON host which possesses strong crystal field and chemical stability.What's more,the influence of Mn2+ ions on luminescence properties and thermal-stability have been studied in details.1.Synthesis and Luminescent Properties of Eu2+ and Mn2+ ion co-doped Ca-a-sialon phosphorsMn2+ and Eu2+ co-doped Ca-?-sialon phosphors,with compositions of Ca0.92-xSi9Al3ON15:0.08Eu2+,xMn2+(x=0-0.10),were designed and synthesized by solid state reaction method.The luminescent properties have been also investigated.The main conclusions are as follows.(1)The phosphors exhibit a strong yellow emission corresponding to the 4f-5d transitions of Eu2+,under UV excitation of 375 nm.The emission intensity arrives the strongest with the low concentration of Mn2+,indicating that there exists energy transfer between Mn2+ and Eu2+,and the major energy transition mechanism is multipolar interactions.(2)Importantly,the introduction of Mn2+ ion effectively improves the fluorescence thermal quenching behavior of the as prepared phosphors is remarkable and possesses over 80%at higher 275? and 98%at 150?of initial emission intensity tested at room temperature.And it's thermal activation energy ?E was calculated to be 0.28 eV.(3)The high internal quantum efficiency(QE)of 72.4%was obtained with the optimum concentration of 0.02Mn.Meanwhile,Excited by the blue light source of 460 nm,it could achieve w-LED with high R,(74.7),and it's CIE and color temperature is(0.314,0.338)and 6345 K,respectively,showing a potential application in w-LEDs2.Synthesis and Luminescent Properties of Mn2+ ion single-doped Ca-a-sialon phosphorsThe transition metal Mn11 doped Ca-a-sialon phosphor with compositions of Ca1-xSi9Al3ON15:xMn2+(x=0.02-0.16)was designed and successfully prepared by high-temperature solid-state method.The luminescent properties have been also investigated.The main conclusions are as follows.(1)The produced Mnri doped Ca-a-sialon phosphor exhibits a dominant red emission centered at~600 nm upon UV light excitation of 265 nm,which is ascribed to the characteristic 4T1(4G)-6A1(6S)transition of Mn2+ with the band gap 4.52 eV.The other emission around 400 nm was derived from vacancy defects in phosphors(mainly oxygen deficiency)confirmed by EPR test.(2)The Mn2+ ion was successfully entered into the structure lattice proved by MPMS magnetic test.Considering the XRD diffraction results,ion radius and energy bond length,Mn2+ ions not only incorporated into the "separate interstitial sites",but also substitute for the Al3+ sites.(3)Otherwise,this phosphor possesses a higher activation energy up to 0.284 eV and shows a great thermal stability of luminescence with 90%initial emission intensity at 150?,nearly unchanged CIE chromatic coordinates,and a good color stability.(4)With the increase of Mn2+ concentration,the fluorescence decay life and the inter quantum efficiency were accelerated.The Energy transfer efficiency between Eu and sialon host is 26.78%?The critical transfer distance was calculated by Blasse's formula and Dexter's formula simultaneously,indicating the dipole-quadrupole(d-q)interaction is the major mechanism for concentration quenching in Ca-a-sialon:xMn2+ phosphor.3.Synthesis and Luminescent Properties of Eu2+ and Mn2+ ion co-doped ?-sialon phosphorsThe ?-sialon:0.05Eu2+,yMn2+ and ?-sialon:0.08Eu2+,yMn2+ phosphors,Si6-zAlzOzN8-z:xEu,yM(x=0.05 ? 0.08,y=0-0.12),were designed and synthesized by using mesoporous SB A-15 as hard templates and combing with carbothermal reduction nitridation method.The luminescent properties have been also investigated.The main conclusions are as follows.(1)With the changes of Eu2+ ion concentration and synthesis temperature,p-sialon:0.05Eu2+,yMn2+ phosphor shows a deep blue emission,while p?sialon:0.08Eu2+,yMn2+ shows a blue-green emission,under UV excitation of 270 nm.(2)Mnll ions are also used as sensitizers,which significantly improve the luminescence intensity of phosphor.The energy transfer between EuLl and Mn2+ ions mainly happens in "nitrogen-rich" environment(525 nm green emission).(3)Considering the XRD diffraction results,ion radius and bond length,Mn2+ ions substitute for the Al3+ sites for all the samples.(4)p-sialon:0.05Eu2+,yMn2+ phosphor possesses a higher activation energy up to 0.291 eV and shows a great thermal stability of luminescence with 75%initial emission intensity at 275? and 97%initial emission intensity at 150 ?.(5)Mixed with Ca-a-sialon:0.12Mn2+red phosphors and ?-sialon:0.08Eu2+,0.12Mn2+blue-green phosphors,it could achieve a w-LED with high Ra(93.1)and it's color temperature is 6345 K,respectively,showing a potential application in w-LEDs... |
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