Design and Synthesis of Diphase Phosphors and the Mechanism of Self-reduction Luminescence of Rare-earths Ions in Matrixes

Author:Lin Yi Zuo

Supervisor:lian shi xun


Degree Year:2018





The silicate phosphor has been widely studied in the field of phosphor because of easy availability of raw materials,the low manufacturing cost,chemical and thermal stability as well as many kinds of crystal structures.This work investigated the synthesis method and luminescence mechanism of silicate phosphors and prepared a series of phosphors based on alkaline earth silicates.1.A series of Eu/Tm/Sm/Yb doped BaZnSi04 phosphors were prepared by high temperature solid-state method and the mechanism of self-reduction was discussed.Self-reduction phenomenon were observed in the samples of Eu/Tm/Yb-doped BaZnSi04 but have not observed in Sm-doped samples.Compared with RA condition,the ca.percent of the reductive concentration of Eu/Tm/Yb in the phosphors BaZnSiO4 prepared in oxidizing atmosphere(OA)condition are 21%,15%and 35%,respectively.Self-reduction ratio of rare earth ions in BaZnSi04 have been explained by ionization energy,potential,electronegativity,radii of ions and crystal structure.It was found that both BaZnSiO4:Eu2+/3+ and BaZnSi04:Tm2+/3+ prepared in air shown greatly broad band emission peak at 500 nm under the excitation of ultraviolet(UV),which indicated they are potential phosphors for UV-based LED.The factors related to self-reduction degree have been also discussed.The successful synthesis of BaZnSi04:RE2+/3+(RE = Eu,Tm,Sm,Yb)phosphors in air provides a new route to obtain other novel orthosilicate-based materials.2.We synthesized a series of(1-x)BaMSiO4·xBa2MSi2O7:Eu2+/3+(M =Zn,Mg)diphase phosphors by a high temperature solid-state reaction in air condition.Then we analyzed the change of luminescence property of low-valence Eu2+ related to the phase transform from BaMSi04 to Ba2MSi2O7.These results show that when the four compounds are pure phases respectively,the self-reduction ability of Eu3+ is not the best.When two phases are in a proper ratio in the matrix,Eu3+ ions will get the highest reduction ability.This phenomenon was explained by the defect theory,and the heterostructure between the two matrix phases BaMSiO4 and Ba2MSi2O7 improves the self-reduction process.3.Eu,Ce co-doped BaZnSiO4·Ba2ZnSi2O7 diphase phosphors with white emission were prepared by a high temperature solid-state reaction.Controlling the phase ratio in diphase phosphors and Ce3+ doping can adjust the luminescence property,and we discussed the energy transfer process and mechanism between Ce3+ and Eu2+/3+ ions.4.Fine controllable blue emission CamSr2-m-nBanSiO4:Ce3+,Li+ solid solution phosphors were synthesized by a high temperature solid-state reaction.The approximation of the crystal field splitting and the centroid shift of 5d energy level were obtained from the spectrum for Ca2SiO4,Sr2SiO4 and Ba2SiO4 phosphors.With the increase of the doped ion radius,the emission peak wavelength red shift firstly from 417 nm of Ca2SiO4 to 438 nm of Sr0.3Ca1.6SiO4 then blue shift to 401 nm of Ba2SiO4.5.A series of solid solution phosphors SrmCa2-mSiO4 codoped with Ce3+,Tb3+,Eu3+ were synthesized by traditional high temperature solid-state reaction.Within a certain Sr/Ca ratio and rare-earth ion doping amount,the solid-solution phosphor can realize full spectra emission,and the emission band is close to the sunlight emission.This phosphor has a potential application value for white phosphor for LED-based UV-chip using in illumination and plant growth light.