CdS/ZnO纳米复合结构制备及荧光特性研究

为增强CdS纳米粒子的荧光强度,以及稳定性,研究了Cd,S不同质量比,有无稳定剂等条件下CdS纳米粒子的制备及荧光特性。在碱性条件下,利用水热法合成了CdS/ZnO的纳米复合结构,并对所有样品进行了XRD、荧光光谱和SEM表征。测试结果表明所制备的CdS纳米粒子和CdS/ZnO的纳米复合结构粒子成分单一且纯净;ZnO复合在CdS表面;在紫外光(328.5nm)激发下,CdS/ZnO纳米复合结构的发射峰位于463nm处,峰形窄而对称,CdS/ZnO纳米复合结构的荧光强度比CdS纳米粒子的荧光强度有显著增强,且CdS和ZnO物质量之比为1∶1条件下,荧光强度最高,其荧光效率比单一CdS纳米粒子高出11%。通过第一性原理计算结果表明,CdS能带结构中,Cd-4d,S-3p和Cd-5s能带分别由5条、3条和1条能级构成,对比不同轨道的分态密度强度,看出CdS的导带边主要由Cd-5s轨道贡献,而价带边主要由S-3p轨道贡献,能量在-7eV附近的电子态主要由Cd-4d轨道贡献。而ZnO上价带主要由O-2p电子构成,靠近费米能级的价带区域则主要由Zn-3d电子贡献,在导带部分,主要来源于Zn-4s和O-2p电子。由于在两种材料的复合结构中Zn-3d电子的能级和S-3p电子的能级接近,存在着二型带阶结构使能带变窄,容易形成跃迁,减小电子-空穴的复合,从而促进复合结构荧光效率的提高。

Synthesis and Fluorescence Property of CdS/ZnO Composite Structure

In order to enhance the fluorescence intensity and reliability of CdS nanoparticles,synthesis,fluorescence property of CdS by different mass ratio of Cd to S,and influence of stabilizer were studied.CdS/ZnO composite structures were synthesized in alkaline condition using the hydrothermal synthesis method.In addition,all samples were tested by XRD,fluorescence spec-troscopy and SEM.The results showed that CdS nanoparticles and CdS/ZnO composite nanoparticles were single and relatively pure.ZnO coated on the surface of CdS.Under the 328.5 nm ultraviolet excitation,emission spectrum was narrow and symmet-rical,and the emission peak was at 463 nm.The fluorescence intensity of CdS/ZnO composite structure nanoparticles increased obviously.The best mass ratio of CdS to ZnO was 1:1 ,whose fluorescence efficiency was 11% higher than that of CdS nanop-articles.The results of first principle study indicated that the energy band of Cd-4d,S-3p and Cd-5s were comprised of 5,3 and 1 energy levels,respectively,in the band structure of CdS.By comparing partial density of states in different orbits,it can be seen that the boundary of conduction band was mainly comprised of Cd-5s orbit,the boundary of valence band was mainly com-prised of S-3p orbit,and the electronic states near -7 eV was mainly comprised of Cd-4d orbit.In the band structure of ZnO, valence band on top was mainly comprised of O-2p electron,the region near Fermi level was mainly comprised of Zn-3d electron, conduction band was mainly comprised of Zn-3d and O-2p electron.In CdS/ZnO composite structures,energy levels of Zn-3d e-lectron were near energy levels of S-3p electron and presented a type-Ⅱ band structure,thus narrowing band-gap.The electron transition became easier,depressing the recombination of electrons and holes,and improving the efficiency of fluorescence.