Preparation And Luminescence Properties Of Rare Earth Activated Silicate Luminescent Materials

Phosphors are an important part of LED devices.In order to obtain efficient light-emitting properties,many new types of phosphors have been studied and reported in recent years.Among phosphors,silicate-based phosphors have become research hotspots due to their variety,and they have great potential to be used as LED phosphors.In this dissertation,a series of novel luminescence materials were synthesized,a variety of rare earth ions were introduced into the silicate matrix to change the type of cations in the crystal lattice.The luminescence properties,the material phase,micromorphology and photoluminescence were discussed by using XRD,SEM,fluorescence spectrophotometer and phosphorescent.Several kinds of multi-color emission silicate-based phosphors suitable for the excitation of near ultra-violet light source were investigated.This dissertation focuses on the following:1)A series of(Lu_1-xY_x)₂SiO₅:yCe³⁺and(Lu_1-xY_x)₂Si₂O₇:yCe³⁺silicate-based phosphorsA series of(Lu_1-xY_x)₂SiO₅:yCe³⁺,(Lu_1-xY_x)₂Si₂O₇:yCe³⁺silicate-based phosphors were synthesized under a reducing atmosphere by using high temperature solid-state method.The results showed that the substitution of Lu³⁺for Y³⁺did not change the crystal structure,the phase purity of silicate phosphors was high,and the structure was monoclinic.Luminescence of(Lu_1-xY_x)₂SiO₅:yCe³⁺phosphors had two emission centers.Ce³⁺replaced Lu³⁺ions,Lu1 and Lu2 were distributed at 8f states with 6 and 7 coordination respectively.(Lu_1-xY_x)₂Si₂O₇:yCe³⁺phosphor had only one emission center,and Ce³⁺replaced Lu³⁺ions located on 4g states.Both phosphors had wide-spectrum excitation bands.The transition from the 5d energy level to the ²F_5/2 and ²F_7/2 energy levels was deconvoluted into two Gaussian emission peaks in Ce³⁺ions.The luminescence intensities of both phosphors reached a maximum when the doping concentration of Ce³⁺was 0.005.After that,the Ce³⁺ions concentration was quenched due to exchange interactions,and the luminescence intensity decreased.2)A series of Na₃LuSi₂O₇:RE³⁺(Ce³⁺,Tb³⁺,Eu³⁺,Dy³⁺,Sm³⁺)silicate-based phosphorsNa₃LuSi₂O₇:RE³⁺(Ce³⁺,Tb³⁺,Eu³⁺,Dy³⁺,Sm³⁺)silicate-based phosphors were synthesized by high temperature solid-state method.Under 350 nm excitation,the Na₃LuSi₂O₇:Ce³⁺phosphors were an asymmetric emission spectrum with a bimodal structure.The emission peak located 418 nm and the emission band was separated into four bands centered at 390,412,444,and 502 nm,which were due to Ce³⁺occupying four difference Na⁺lattices.The emission spectrum of Na₃LuSi₂O₇:Tb³⁺showed a wavelength range from 370 nm to 700 nm with characteristic peaks at 485,542,594 and 625 nm.At the same time,the properties of photoluminescence and cathodoluminescence were compared.The main emission at 542 nm were due to ⁵D₄?⁷F₅ transition of Tb³⁺ions.There existed the energy transfer of Ce³⁺?Tb³⁺in Na₃LuSi₂O₇:Ce³⁺,Tb³⁺phosphors.With the increase of Tb³⁺ions doping concentration,while the concentration of Ce³⁺ions was fixed,it could be clearly seen in the chromaticity diagram that the color of Na₃LuSi₂O₇:0.05Ce³⁺,yTb³⁺?y=0?0.09?phosphor transitions from blue light to green light.Na₃LuSi₂O₇:RE³⁺(Eu³⁺,Dy³⁺,Sm³⁺)phosphors were synthesized,and the luminescence properties of the three phosphors were systematically studied.Under near-ultraviolet excitation,the energy transfer relationship between Dy³⁺and Eu³⁺ions was analyzed,which achieved white light emission.3)A series of NaCaGaSi₂O₇:RE³⁺(Ce³⁺,Tb³⁺,Eu³⁺,Dy³⁺,Sm³⁺)silicate-based phosphorsNaCaGaSi₂O₇:RE³⁺(Ce³⁺,Tb³⁺,Eu³⁺,Dy³⁺,Sm³⁺)phosphors were synthesized by high temperature solid-state method and the rare earth ions replaced the Ca²⁺ions lattice.For the NaCaGaSi₂O₇ phosphors doping with Ce³⁺,it had strong absorption under the near ultraviolet around 330 nm.And the emission spectrum was a broadband located at 380 nm,which was due to the 5d?4f transition of Ce³⁺.The sample with the highest luminescence intensity was NaCaGaSi₂O₇:0.03Ce³⁺.NaCaGaSi₂O₇:Tb³⁺phosphors emited intense green light with a emission peak of 542 nm under the excitation of 377 nm.Dipole-dipole interaction explain the Tb³⁺ions concentration quenching of luminescence.The energy transfer mechanisms of NaCaGaSi₂O₇:Ce³⁺,Tb³⁺,NaCaGaSi₂O₇:Eu³⁺,Dy³⁺and NaCaGaSi₂O₇:Sm³⁺,Dy³⁺phosphors were dipole-dipole interaction,dipole-quadrupole interaction and non-radiative transition.NaCaGaSi₂O₇:Eu³⁺,Dy³⁺and NaCaGaSi₂O₇:Sm³⁺,Dy³⁺phosphors achieve white light emission.