核-壳结构ZnS∶Tb/CdS纳米晶的电致发光

Organic Electroluminescence of Core-Shell Structure ZnS ∶Tb/CdS Nanocrystals

利用微乳液方法合成出粒径为4 nm的核-壳结构ZnS∶Tb/CdS纳米晶。用XRD、TEM及荧光光谱等手段对合成的纳米晶的结构、形态和光学特性分别进行了表征。将ZnS∶Tb/CdS纳米晶制作成有机-无机杂化结构电致发光器件,其结构为ITO/poly(3,4-ethylene d ioxythiophene)∶poly(styrene sulfonate)(PEDOT-PSS)(70 nm)/poly(vinylcobarzale)(PVK)(100 nm)/ZnS∶Tb/CdS纳米晶(120 nm)/2,9-d im ethyl-4,7-d iphenyl-1,10-phenanthroline(BCP)(30 nm)/L iF(1.0 nm)/A l(100 nm)。当驱动电压为13 V时,可以测到Tb3+离子的两个特征峰。在电致发光光谱中未测到聚合物PVK的发光,说明电子和空穴是在纳米晶层上复合的。当驱动电压为25 V时,得到器件的最大亮度为19 cd/m2。

Core-shell structure ZnS ： Tb/CdS nanocrystals（NCs） with sizes of about 4 nm were synthesized via reverse microemulsion technique. The structures, shapes and characteristic optical properties of ZnS ： Tb/CdS NCs were characterized by means of X-ray powder diffraction （XRD）, transmission electron microscopy（ TEM ） and F-4500 Fluorescence spectrometer. The XRD pattern of ZnS ： Tb/CdS NCs was shown that the crystals exhibit zinc-blend crystal structure. The three diffraction peaks are corresponding to （111 ）, （220）, and （311） planes of the cubic crystalline ZnS, respectively. Due to the size effect, the XRD peaks were broadened and their widths become larger as the crystals become smaller. From the XRD analysis, no characteristic peaks of impurity phases were observed. The average sizes of ZnS ： Tb/CdS NCs were calculated from the Debye-Scherrer equation to be around 3 nm. From typical TEM image, it is noticed that the average size of the ZnS ： Tb/CdS NCs is about 4 rim. So the thickness of CdS shell is evaluated to be about 0.5 nm. The PL spectra of ZnS ： Tb/CdS excited by 379 nm are composed of three peaks located at 489, 543, and 583 nm, which is assigned respectively to ^5 D4→^7 F6,^ 5 D4→^7 F5, and ^5 D4→^7 F4 electron transitions of Tb^3＋ ions. An electroluminescent （EL） device having a hybrid organic/inorganic multilayer structure of ITO/ poly（3,4-ethylene dioxythiophene） ： poly （ styrene sulfonate ） （ PEDOT-PSS ） （ 70 nm ）/poly （ vinylcobarzale ） （ PVK ） （ 100 nm ）/ ZnS ： Tb/CdS NCs （120 nm）/2,9-dimethyl -4,7- diphenyl-1,10-phenanthroline （BCP）（30 nm）/LiF （1.0 nm）/Al （ 100 nm） was fabricated. The two peaks located at 546 nm （^5D4→^7F5 ） and 577 nm （^5D4→^7F4 ） of the Tb^3＋ center were observed when the EL device was driven at applied bias of 13 V. It is also noticed that EL emission from PVK in the device was not observed, indicating that the electron-hole would be recombined in ZnS ： Tb/CdS NC layer. The maximum luminance of 19 cd/m^2 was obtained under the applied bias of 25 V.