Photoluminescence Study of ZnO Nanosheets with embedded Cu Nanocrystals.
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Photoluminescence Study of ZnO Nanosheets with embedded Cu Nanocrystals. Aaron I. Diaz Cano and Brahim El Filali, 1 UPIITA – Instituto Politécnico Nacional, México D. F. 07738, México. ABSTRACT In this work a simple method to produce the ZnO nanosheets (NSs) with inclusions of Cu nanocrystals by means of electrochemical etching without the necessity of any surfactant has been presented. The Raman spectroscopy demonstrates that the amorphous samples of ZnO-Cu present appreciable changes in its vibrational behavior after the thermal treatment at 400oC in ambient atmosphere. The study of Photoluminescence (PL) shows monotonous increasing the bands centered in 3.07, 2.41, 2.03 and 1.57 eV versus etching time in freshly prepared samples. The intensity variation of the PL bands, the changes in vibrational behavior, as well as the impact of the copper content and preparation conditions allow identifying emission inside the visible spectral range related to the surface defects that is interesting for the future possible application this ZnO system in room temperature “white” light-emitting diodes. INTRODUCTION ZnO nanostructures have been one of the most popular materials in recent years [1,2]. ZnO nanostructures have attracted considerable attention due to their promising applications in electronic, photoelectronic and sensing devices, mainly due to the potential for engineering the properties not obtained in the bulk materials. For this reason, the electrochemical technique has greater potential to control the dimensionality through the variations of electrolyte composition, the process duration and applied potential at room temperature. Thus it allows the precise control of reaction conditions. Recently, researchers have found that some doping elements can influent on the luminescence properties of ZnO nanostructures [3–5]. Copper is a prominent luminescence activator for the II–VI compounds [8]. The diffusion of Cu into ZnO can cause the formation of defects (CuZn, Cui). The rich defect chemistry of porous ZnO-Cu NSs permits to expect a great variety of photoluminescence (PL) bands in the visible spectral range [6,7]. However, the majority of these defects remain unidentified and optical transitions responsible for the PL bands need to be verified. Actually it is not clear the relations between the defects appeared and the structural properties of ZnO-Cu nanosystems. In this work ZnO-Cu nanosheets were prepared by the anodization method and their optical properties have been studied before and after thermal annealing. EXPERIMENT Electrochemical anodization of Zn foils was performed in a two-electrode system including the Cu electrodes exposed to the electrolyte. The distance between them was 9 mm. The pieces of a Zn foil (Aldrich 99.99% purity, 0.25 mm thickness) with a radius of 6 mm were treated in acetone and ethanol for 15 min with ultrasonic cleaning and then washed with deionized water. All electrolytes were prepared from chemical reagents (Aldrich) and deionized water. The electrolyte composition was a 1:10 volum
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