摘要
发光是物体将以某种方式吸收的能量转化为光辐射的过程。全固态照明光源(半导体发光二极管,简称LED)被认为是21世纪最具有发展潜力的高技术领域之一。稀土离子Eu3+是一种良好的红光发光中心,它的激发谱峰位于395 nm左右,Li+为低价电荷的补偿离子和发光敏化剂。本课题根据在ZnO基质中掺杂稀土离子Eu3+作为分立发光中心的设想,采用脉冲激光沉积(pulsed laser deposition,即PLD)薄膜外延技术,制备并初步研究了Eu3+、Li+共掺杂ZnO薄膜的结构及光学性质。
控制Si衬底温度为400℃的情况下,调节真空室氧压分别为0Pa、2×10-2Pa、2×10-1Pa以及2×100Pa时制备ZnO:Eu3+, Li+/Si薄膜。通过X射线衍射仪和荧光分光光谱仪测试了样品的晶体结构与发光特性。XRD谱表明,Eu3+、Li+共掺杂的ZnO薄膜具有c轴择优取向,XRD谱中除ZnO晶向以外没有出现其它结晶峰,表明掺杂元素Eu3+、Li+均已进入到ZnO晶格中,形成了以Eu3+为发光中心的ZnO纤锌矿结构。当以395 nm的激发光照射样品时,在PL光谱中观察到了稀土Eu3+在594 nm、613 nm附近的特征发光峰。
在背底真空为10-5Pa时,充入氧气,控制氧分压为2×10-1 Pa,改变衬底温度,分别在室温、100℃、200℃、300℃、400℃和500℃时,制备Eu3+、Li+共掺杂的ZnO薄膜。同样测得其XRD谱线与室温下的PL谱。分析图谱可知,稀土离子能有效掺进ZnO晶格中,得到高度c轴择优取向的单晶薄膜。温度较低时,用325 nm的激发波长激发,观察不到Eu3+的本征发光峰,ZnO与Eu3+之间没有进行有效的能量传递；但温度较高的情况下,所制备样品的PL谱中出现Eu3+的本征发光峰,分析认为是较高的温度下,Eu3+可以获得足够的迁移能进入到ZnO晶格内部,有利于从基质向稀土离子传递能量。
当ZnO基质中掺杂离子Eu3+、Li+的掺杂浓度降低时,测得所制备样品的PL谱,Eu3+本征发光峰的强度增强,认为可能是当浓度超过某一值时发生了一定程度的猝灭。
Emitting light is a process that the substance gives out energy after absorbing radiation in some way. Solid-state light sources (light emitting diodes, LEDs) are considered one of the most potential high-tech areas in the 21st century. Rare earth ion Eu3+is a good red luminescence center, and its excitation spectrum peak is at about 395nm, Li+ions act as the low compensation charge and luminescence sensitizer. In this dissertation, Eu rare earth was doped into the ZnO matrix as the separate luminescence center by the pulse laser deposition method, and the crystal structure and optical properties of the films were studied.
ZnO:Eu3+, Li+/Si films were prepared on silicon substrates under the substrate temperature of 400℃by PLD technology at different oxygen pressures. The crystal structure and optical properties were studied with the X-ray diffractometer and fluorophotometer. By the X-ray diffraction, it can be seen that the ZnO:Eu3+, Li+films are highly c-axis oriented. In the XRD spectrum, no other crystal orientations are observed except the ZnO crystal orientation, which indicates that the doping elements of Eu3+and Li+have incorporated into the crystal lattice of ZnO, and conform the wurtzite structure with Eu3+as its luminescence centre. When irradiated under the wavelength of 395nm, obvious emission at the wavelength of about 594 nm,613 nm from the rare-earth element of Eu3+can be observed in the photoluminescence spectra.
Eu3+、Li+co-doped ZnO films were prepared under different substrate temperature with the 2X10-1 Pa oxygen partial pressure. The XRD spectrum and PL spectrum at room temperature were measured. The results show that rare earth ions can be effectively coped into the ZnO crystal, and the single crystal films are of high c-axis. When the temperature was low, the Eu3+ emission peak could not be observed under the excitation light of 325 nm wavelength, there were not effective energy transfer between ZnO matrix and the doped Eu3+ions; while the temperature was high, the Eu3+emission peak appeared under the 325 nm wavelength excitation in the PL spectra. It can be concluded that the rare earth ions of Eu3+can obtain sufficient transferring energy to enter the ZnO crystal lattice which is helpful for the energy transfer from ZnO matrix to the rare ions.
When the doping concentration of Eu3+、Li+in the ZnO matrix decreases, the intensity of the Eu3+intrinsic luminescence peak in the PL spectra increases under the same conditions. That may be because when the concentration exceeds a critical value, the quenching occurs to some extent.
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