Design,Synthesis And Performance Research Of Color-tunable Silicate And Phosphate Phosphors With Application For White-LEDs

In the paper,a series of color-tunable CSMS,CSMS:Eu2+,Mn2+ and Ba2Ca1-xM,(PO4)2:Eu2+(M=Mg,Sr,Zn)phosphors were synthesized by high temperature solid state reaction technique that was supplemented by the way of rare earth doping and multi-cations substitutions.in which Ca0.75Sr0.2Mg1.05(Si2O6)(CSMS)and Ba2Ca(PO4)2(BCPO)played the role as hosts.Moreover,we have carried out the detailed discussion and research about some unusual phenomenon,such as emission was derived from the oxygen vacancy defects of host,energy transfer between host and doped atoms,abnormal red-shift(blue-shift)of emission spectra and thermal back-transfer over the barrier of the characteristic temperature spectra because of multi-cations substitution:(1)The host of Ca0.75Sr0.2Mg1.05(Si2O6),which has defect luminescence,was synthesized by high-temperature solid-state method in reductive atmosphere,and the defect luminescence of host has been studied in detailed by analyzing the crystal structure,luminescence process excited by host and temperature characteristic curve.The CSMS host appears as an orange-yellow emitting under the irradiation of ultraviolet lamp.Through the measurement of fluorescence spectra,the emission spectra of CSMS host present a broad emission band from 350 to 800 nm,which shows two distinct emission peaks,453 nm and 580 nm,respectively.In addition,the blue-shift,red-shift and intensity changes of temperature dependence emission spectra in Ca0.25Sr0.2Mg1.05(Si2O6)host are observed with higher temperature.(2)Doping Eu2+ and Mn2+ ions into CSMS host,a series of Ca0.250.75-xSr0.2Mg1.05-y(Si2O6):xEu2+,yMn2+ phosphors were synthesized by high-temperature solid-state method.In this paper,the fluorescence spectra,color coordinate;quantum yield,thermoluminescent spectra,diffuse reflectance spectra and fluorescence lifetime decay curve of samples have been studied in detailed.For Eu2+ single-doped,these phosphor samples have an obvious absorption in the near-ultraviolet and blue region with a wide band of excitation spectrum ranging from 200 to 450 nm monitored at 453 nm.The maximum quantum yield in as-prepared Eu2+ sing-doped samples can reach 66.08%and typical CIE chromaticity coordinates is(0.1451,0.0736).Mn2+ single-doped CSMS presents the emission with the main peak at 680 nm under the excitation of 415 nm.For Eu2+ and Mn2+ co-doped,the energy transfer of Eu2+?Mn2+,Eu2+?host and host?Mn2+ can be demonstrated,and there should be a blue-white emission in CSMS:0.03Eu2+,0.02Mn2+with CIE(0.2682,0.2056).(3)In the paper,the possibilities of color tuning of the efficient LEDs phosphor Ba2Ca1-xMx(PO4)2:Eu2+(M=Mg,Sr,Zn,x=0.0-1.0)and Ba2Ca1-x-yMgxSry(PO4)2:Eu2+(x=y=0.1-0.5)series were investigated by multi-cations substitution.A new mechanism of direct/indirect substitution of Eu2+ for the host that containing more than one cation and a concept of "selective excitation" for multiple luminescence center system have been proposed.Here,the emission presents an abnormal red-shift(479?602 nm)in Ba2Ca1-xMgx(PO4)2:Eu2+ series and an abnormal blue-shift(485?441 nm)in the Ba2Ca1-ySry(PO4)2:Eu2+.For the Ba2Ca1-zZnz(PO4)2:Eu2+ series,the emission blue-shifts firstly from 494 to 442 nm and then red shifts from 442 to 585 nm when excited by 355 nm,while a continuous red-shift was observed under the excitation of 400 nm.Three different existence patterns(solid solution material,transition state of mixture and new host component)of phosphor have presented when introducing a great deal of foreign cations to the original host.And the energy transfer and thermal back-transfer over the barrier are demonstrated in as-prepared samples.What's more,a warm white-emitting LED chip with the CIE chromaticity coordinates of(0.3622,0.3051),the color rendering index(Ra)of 88.7 and correlated color temperature(CCT)of 3947 have been realized using as-prepared phosphors.