纳米ZnO薄膜可见发射机制研究

利用溶胶－凝胶法 （Sol-Gel）制备了纳米ZnO薄膜，获得了高强的近紫外发射室温下测量了样品的光致发光谱(PL )、吸收谱(ABS)、X射线衍射谱(XRD).X射线衍射(XRD)的结果表明：纳米ZnO薄膜呈多晶态，具有六角纤锌矿结构和良好的C轴取向；发现随退火温度升高，（002）衍射峰强度显著增强，衍射峰的半高宽（FWHM）减小、纳米颗粒的粒径增大.由吸收谱(ABS)给出了样品室温下带隙宽度为3.30 eV.在PL谱中观察到二个荧光发射带，一个是中心波长位于392 nm附近强而尖的紫带，另一个是519 nm附近弱而宽的绿带研究了不同退火温度样品的光致发光峰值强度的变化关系，发现随退火温度升高，紫带峰值强度增强、绿带峰值强度减弱，均近似呈线性变化.证实了纳米ZnO薄膜绿光发射主要来自氧空位(Vo)形成的浅施主能级与锌空位(VZn)形成的浅受主能级之间的复合，或氧空位(Vo)形成的深施主能级上的电子至价带顶的跃迁；紫带来自于导带中的电子与价带中的空位形成的激子复合.

Study on the Visible Emission Mechanism of Nanocrystalline ZnO Thin Films

Nanocrystalline ZnO thin films is a promising material for short-wave laser and luminescence etc, due to its wide band gap (3.37 eV) and high exciton binding energy(60 meV)at room temperature.The high-quality nanocrystalline ZnO thin films is prepared by using sol-gel, grow on quartz glass subtractes, Photoluminescence spectra and Absorption spectra of nanocrystalline ZnO thin films with excitation wavelength 330 nm are measured at room temperature. Two emission bands are observed, one being a strong and narrow ultraviolet emission band its central wavelength is 392 nm and the other being weak and wide green visible band its central wavelength is 519 nm.Crystal structure of samples are examined by X-ray diffraction (XRD) pattern, the mean grain size of nanocrystalline ZnO thin films are calculated by with Debye-Scherrer formula. The results indicate that nanocrystalline ZnO thin films has a hexagonal wurtzite structure and polycrystalline, and showed sharp diffraction peak for ZnO(002),which indicate that as-sputered film were highly c-axis oriented. The grain increases with annealing temperature, Absorption spectra of ZnO thin films indicated that the band gap of the thin films was 3.30 eV . Photoluminescence spectra showed that ZnO thin films emitted strong UV Photoluminescence .The intensities of PL peaks decrease with increasing annealing temperature. In particular the mechanism behind the visible luminescence has also been discussed in this paper.It should be said that the mechanism behind the visible luminescence is still a question to debate. In this paper the visible emission processes of nanocrystalline ZnO. The experiments prove that the luminescence emission peak located 519nm corresponds to the transition from the shallow level of oxygen vacancy to the shallow level of zinc vacancy or electron transition from deep level of oxygen vacancy to valence band.