Preparation And Luminescence Properties Of Re³⁺- Doped Y₂O₃-Al₂O₃-Sc₂O₃ Ternary Ceramic Phosphors

Rare-earth doped transparent cereamics?e.g.,YAG:Ce?have drawn sufficient attentions due to their superiorities in luminescence property,heat-conductive property and chemical&physical stability,further becoming the preference in high power-density drived light-emitting devices.YAG:Ce transparent ceramics performed excellent in quantum efficiency as excited by 450 nm light sources with high power or high power density,however,the deficiency in red components in the emission spectra has resulted in poor color rendering index as they are applied in white light-emitting diodes and displays.Therefore,it is critical for improving the luminescence quality that the red light component in the emission spectra of YAG:Ce ceramics is enhanced.Previous studies indicated that increasing the doping concentration of Ce³⁺in the matrix would promot the red-shift of the emission spectra of Ce³⁺.However,the solubility of Ce³⁺in YAG crystal lattices is limited due to that Ce³⁺has a larger ionic radius than that of Y³⁺.More importantly,the concentration quenching would happen and the luminous efficiency would decrease with increased Ce³⁺concentration.Thus,one of the research targets of this thesis is overcoming the luminous efficiency decrease issue during realizing the red-shift of emission spectra.Al³⁺ions are designed to be substituted by Sc³⁺ions with larger ionic radius so that lattice-expanded YSAG transparent ceramics are obtained,which greatly increase the doping concentration of Ce³⁺in the matrix.Therefore,in the present work,we have studied the Y₂O₃-Al₂O₃-Sc₂O₃ system solid solution from the following three aspects:?1?The 3Y₂O₃-5Al₂O₃-5x Sc₂O₃ ternary ceramics?YSAG?were fabricated using the solid-state reactive method.The results indicated that YSAG solid solutions with expensed lattice parameters can be obtained as x=0?44 at.%in 3Y₂O₃-5Al₂O₃-5x Sc₂O₃.According to XRD and ⁴⁵Sc and ²⁷Al NMR spectrum,most of Sc³⁺ions occupy the site of dodecahedron,the remained ones occupy the octahedron sites.In addition,the disordered crystal field with Sc³⁺incorporation increased and the emission spectrum of Ce³⁺was broadened.?2?On the basis of YSAG:m Ce³⁺?x=44 at.%?,the effects of Ce³⁺doping concentration?m=0.2%?5.0%?in YSAG on the constitutions,microstructure and luminescence properties have been studied.The solid solution phosphor ceramic showed a largest red-shift of 26 nm and a broadening of 6 nm of the emission spectrum,along with no obvious concentration quenching.The as-prepared ceramics were irradiated under blue LED and LD,the emission peak intensity gradually increased as the Ce³⁺doping concentration increases from 0.6%to 1.0%.As the Ce³⁺ion doping concentration continued to increase,the emission peak intensity gradually decreased.The reason for the decrease in luminescence intensity is probably that the accumulation of heat in the ceramic,which finally caused thermal quenching.?3?It has been verified that improving the thermal-conductivity of the ceramic phosphors is positive for enhancing the luminous efficiency and luminescence stabililty when the ceramics are excited by high power or high-power density light sources.Therefore,in this work,extra Al₂O₃were incorporated into the 3Y₂O₃-5Al₂O₃-5x Sc₂O₃:m Ce³⁺?x=44 at.%,m=5.0%?ceramic.The spark plasma sintering technology was adopted,and finally Al₂O₃/YSAG:5%Ce³⁺composite ceramic phosphors with different content of Al₂O₃were obtained.The influences of preparation technics and contents of extra Al₂O₃ on the composition,microstructure and luminescence property of the composite ceramics were discussed.The results indicated that the luminous intensity of the composite ceramic phosphor with 40 wt.%Al₂O₃ contents is 2.4 times higher than that of the YSAG:Ce³⁺transparent ceramic.The peak of the emission spectrum is at573 nm,almost the same as that of the YSAG:Ce³⁺transparent ceramic,maintaining high ratio of red components in the emission spectra.Meanwhile,the damage threshold of the composite ceramic under the excitation of high-power density laser light source.