Studies On Luminescence Properties Of Rare Earth Ions Doped Poly-borates

Trivalent rare earth ion have rich energy levels,and the electronic transition modes including f-f,f-d and charge transfer when they are used as the luminescence center.Therefore,the excitation and emission spectra of rare earth doped luminescence materials can cover the infrared,visible and even UV regions,which are widely used in various fields of production and life,such as daily lighting,display,laser and biomarkers.The luminescence properties of rare earth doped luminescent materials are not only dependent on not only the type of doped ions,but also the matrix structure,it is thus particularly important to choose a suitable material as the matrix.Borate is a ki nd of very important optical functional material because of its rich structure and good p hysical and chemical properties.Therefore,we choose borates as the matrix material and rare earth Eu³⁺,Ce³⁺,Tb³⁺and Dy³⁺as the luminescence center to study their photoluminescence properties.The main experimental results showed just like following:1.Completed solid solutions of Y_1-xEu_x[B₆O₉(OH)₃]were prepared by boric acid flux method and the structure of Eu[B₆O₉(OH)₃]was determined by single crystal X-ray diffraction(XRD).The successful Eu³⁺-doping was confirmed by the composition dependent linear change of unit cell parameters obtained by Le Bail fitting against the powder XRD.Thermal treatments on Y_1-xEu_x[B₆O₉(OH)₃]led to the formation of?-Y_1-xEu_xB₅O₉,which can also be prepared by sol-gel method.Systematic PL investigation performed on Y_1-xEu_x[B₆O₉(OH)₃]and?-Y_1-xEu_xB₅O₉ revealed that Y_1-xEu_x[B₆O₉(OH)₃]showed orange emission while?-Y_1-xEu_xB₅O₉emit bright red light under the excitation of CT band and CT absorption is very strong,indicating which shows that?-YB₅O₉ is a good host for Eu³⁺doping indeed.2.A series of phase-pure phosphors?-La_0.9-xCe_0.1Tb_xB₅O₉and?-La_0.9-xCe_0.1Dy_xB₅O₉were prepared by sol-gel method,which was confirmed by Le Bail fitting against the XRD data.By analyzing the photoluminescence spectrum,it is confirmed that there is efficiency energy transfer from Ce³⁺to Tb³⁺and Dy³⁺is as high as 81%and 75.4%,respectively,and the energy transfer mode is due to the dipole-dipole interaction.3.LiSr(Y_1-xEu_x)₂(BO₃)₃?LiSr(Y_1-xTb_x)₂(BO₃)₃ and LiSr(Y_0.7-xTb_0.3Eu_x)₂(BO₃)₃series solid solution phosphors were successfully prepared by high temperature solid state method.After that,we tested the photoluminescence performance of these three series of samples.Under the excitation of near ultraviolet light,LiSr(Y_1-xEu_x)₂(BO₃)₃ emit bright red light,it thus can be considered as the high-quality red phosphor for near ultraviolet white LEDS.LiSr(Y_1-xTb_x)₂(BO₃)₃ emit bright green light was emitted under the excitation of near ultraviolet.Tunable color was achieved in Tb³⁺and Eu³⁺co-doped single phase LiSr(Y_0.7-xTb_0.3Eu_x)₂(BO₃)₃.With the increase of Eu³⁺ doping concentration,the color of the phosphor changed from bright green light to bright red light passing through the yellow light area under the excitation of 365nm.At the same time,the energy transfer efficiency from Tb³⁺to Eu³⁺is as high as 96%.The mechanism of energy transfer is quadrupole-quadrupole interaction.4.PbY_1-xEu_xB₇O₁₃,PbY_0.9-xEu_0.1Gd_xB₇O₁₃and PbY_1-xTb_xB₇O₁₃were synthesized by high temperature solid state method,and their phase purity was investigated by XRD.For PbY_1-xEu_xB₇O₁₃,the ratio of red and orange emission increase along with the content of Eu³⁺,suggesting that the coordination environment Eu³⁺changed from central symmetry to noncentral,which might be attributed to the large cationic size of Eu³⁺in comparison with Y³⁺.A similar result was also observed for PbY_0.9-xEu_0.1Gd_xB₇O₁₃.Moreover,a local site symmetry change was also observed for Tb³⁺in PbY_1-xTb_xB₇O₁₃,which could be deduced from the change of the ratio of cyan light to green light emissions.