紫外光激发Ce3+掺YVO4蓝光发射性能研究

利用提拉法生长了YVO₄和掺2.0at% CeO₂(或Ce₂(CO₃)₃)的YVO₄: Ce³⁺晶体。样品的XRD测试表明Ce³⁺代替Y³⁺进入晶格, Ce³⁺的加入并没有影响YVO₄的晶格结构。XPS测试显示YVO₄: Ce³⁺晶体中Ce离子3d分裂为882.0、885.8、902.9、908.0和915.9 eV等5个峰, 峰位表明样品中铈离子是以Ce³⁺和Ce⁴⁺两种价态形式存在。YVO₄和YVO₄: Ce³⁺激发谱都呈现出260~360 nm宽带激发, 此激发带源于基质中VO₄^3-离子团的配体O到V的电荷迁移吸收。使用325 nm的紫外线激发时, 两种样品均可发出以440 nm 为中心的宽带蓝光,其中YVO₄发射峰应归属于VO₄^3-离子团中³T₂→¹A₁和³T₁→¹A₁跃迁; 而YVO₄: Ce³⁺的蓝光发射则来源于Ce³⁺的5d→4f 的跃迁。分析可知YVO₄: Ce³⁺中VO₄^3-的π轨道和Ce³⁺的电子波函数能有效地重叠, 使得VO₄^3-和Ce³⁺可通过交换作用有效地向Ce³⁺传递能量, 可大幅提高Ce³⁺的蓝光发射强度。实验结果显示YVO₄: Ce³⁺可作为UV-LED管芯激发的白光发光二极管用高亮度蓝色发光材料。

Blue-emitting Properties of Ce3+ Doped YVO4 under Ultraviolet Excitation

YVO₄ and YVO₄:Ce³⁺ single crystals doped with 2.0at% CeO₂ (or Ce₂(CO₃)₃) were grown by using the Czochralski method. XRD pattern shows that Ce³⁺ ion enters the YVO₄ lattice by occupying the Y³⁺ sites and the YVO₄ crystal structure change little by the addition of Ce ions. The X-ray photoelectron spectroscopy (XPS) shows that the Ce (3d) peak splits into five peaks located at 882.0, 885.8, 902.9, 908.0 and 915.9 eV, which indicates that the Ce³⁺ and Ce⁴⁺ ions coexist in both kind of samples. The excitation spectra of YVO₄ and YVO₄:Ce³⁺ crystals are both in the range from 260 nm to 360 nm, due to the charge transfer transition of the O^2--V⁵⁺ ion pairs of VO₄^3- polyhedron. YVO₄ and YVO₄:Ce³⁺ single crystals radiate a wideband blue light centered at 440 nm when excited by 325 nm ultraviolet light, the former corresponds to ³T₂→¹A₁ and ³T₁→¹A₁ transition of VO₄^3-, while the latter corresponds to 5d→4f transition of Ce³⁺. In YVO₄: Ce³⁺ crystal, the wave functions of Ce³⁺ overlaps effectively to the π orbital of VO₄^3-, via this interaction the energy can be transfer effectively from VO₄^3- to Ce³⁺, so that the blue-emitting intensity of Ce³⁺ is improved significantly. Experimental results show that YVO₄: Ce³⁺ crystal is a potential blue-emitting material for white-emitting LED under ultraviolet excitation.