Structural and Photoluminescence Studies of (Cu, Al) Co-doped ZnO Nanoparticles

Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954

Structural and Photoluminescence Studies of (Cu, Al) Co-doped ZnO Nanoparticles5 P. Swapna1, S. Venkatramana Reddy1,a 1 – Department of Physics, Sri Venkateswara University, Tirupati – 517 502, A.P, India a – drsvreddy123@gmail.com DOI 10.2412/mmse.77.36.550 provided by Seo4U.link

Keywords: ZnO nano particles, emission spectra, X-ray diffraction and Elemental analysis.

ABSTRACT. Pristine and co-doped ZnO with doping of Cu and Al nano particles have been successfully synthesized by chemical co-precipitation method without using any capping agent and annealed in air ambient at 5000 C for one hour.

Here, the Al concentration is fixed at 5 mol percent and copper concentration is increasing from 1 to 5 mol percent. The Crystallanity, structure and crystallite size of pure and co-doped ZnO nano particles are determined by X-ray diffraction (XRD) in range from 200 to 800. XRD pattern reveals that the samples possess hexagonal wurtzite structure of ZnO and the estimated particle size of pure and co-doped ZnO nano particles is 20-22nm. Morphological and compositional analysis is done by SEM and EDS. Photoluminescence studies reveals the origin of PL emission in the visible region. PL spectrum shows the blue emission peaks appeared at 435, 448 and 468 nm and green emission peak at 536 nm.

Introduction. ZnO is a promising (II- V) semi conductor with wide direct band gap (3.32 eV) and large binding energy ( 60 MeV). It have attracted a lot of attention due to its significant properties such as room temperature luminescence, good transparency and high electron mobility. Also, it has practical applications in various fields such as solar cells, light emitting diodes, gas sensors, etc.

Preferentially ZnO is in the hexagonal wurtzite structure[1-3]. Electronic structure, optical and electrical properties of the host lattice ZnO can be varied by adding of different type of metal ions such as Ca, Al, Mg, Ni and Fe[4-10]. The magnetic properties of ZnO also tuned by doping of metal ions such as Co, N, Ru and Cu[11-13]. There are different methods for the synthesis of ZnO nano particles such as solution combustion method [14], vapor phase oxidation[15], chemical vapor deposition, sol-gel[16], chemical co-precipitation method[17-19]. Among these methods chemical co-precipitation method is used for the preparation of large quantity of pure and doped ZnO nano particles because it is simple, cost effective and high yield rate. The structural, compositional and optical properties of the synthesized nano particles are presented.

Experimental Procedure. Pristine and co-doped ZnO nano particles have been synthesized using the chemicals Zinc acetate Dehydrate, Potassium Hydroxide, Alluminium Chloride (anhydrous), Copper Acetate Mono Hydrate, which are all highly pure and in analytical grade used in the experiment without any further purification. 0.2 M ZnO nano particles solution has been synthesized by dissolving Zinc acetate in de-ionized water then adding Potassium hydroxide solution drop wise with constant stirring of 10 hrs. To prepare doped ZnO nano particles, the same process is repeated by adding Alluminium chloride and Copper acetate mono hydrate solutions drop wise, keeping alluminium as constant at 5 mol percent and varying the copper concentration from 1 to 5 mol percent under continuous stirring of 10 hrs. After completion of the filtering process the precipitate is washed 5

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Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954

several times with de-ionized water to remove the un reacted chemical species. Then the product is dried in an oven at 700 C for 9 hrs. Now grind the precipitate powder with the help of agate motor until the powder become fine particles. Eventually the powders are annealed in the furnace at 5000 C for one hour. The prepared samples are carefully examined by X-ray diffraction, Scanning electron microscopy, Energy dispersive spectroscopy and photoluminescence.

Results and Discussion: Structural Analysis. Fig.1 shows the XRD pattern of pure and co-doped ZnO nanoparticles. All the peaks in the Fig. are well matched with the standard JCPDS card no 36-1451 and possess hexagonal wurtzite structure. Secondary peaks corresponding to copper or alluminium are never found.

Fig. 1. XRD patterns of (a) pure ZnO, (b)Cu-1 mol%, Al-5 mol%, (c) Cu-2 mol%, Al-5 mol%, (d) Cu-3 mol%, Al-5 mol%, co-doped ZnO nano structure.

This may be attributed to the incorporation of Al and Cu ions into the Zn lattice site rather than interstitial. Contrary to the earlier reports[20- 21], this may be attributed to the limitation of the instrument of the XRD characterization, that small amount of impurities cannot be detected. Particle sizes of pristine and (Cu, Al) doped ZnO nano powders are found to be in the range of 20-22 nm. By increasing the concentration of copper content, the particle sizes are decreases and the intensity of the peak (101) is increases. The crystallite size of nano particles can be calculated using the Debye Scherer formula D=0.91λ /βcosθ , where D is the crystallite size, λ is the wavelength of x-rays and θ is the Bragg’s angle of diffraction. The particle sizes calculated from the formula are decreasing by the increasing of copper doping concentration.

Morphological and compositional analysis. The SEM images of all the samples as shown in Fig. 2, the particles are in regular non uniform, semi spherical shape though agglomeration of primary particles. With the increasing of copper doping concentration, the agglomeration of the particles is reduces. EDAX analysis indicate the successful dopant incorporation of alluminium and copper, which is with the coincidence of XRD result. EDS spectra of pure and doped samples are shown in Fig.3 Elemental analysis shows that all the elements are in stoichometric. Pure ZnO contains only zinc and oxygen elements, where as the co doped samples contains zinc, oxygen, alluminium and copper in the appropriate ratios.

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Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954

Fig. 2. SEM images of (a) pure ZnO, (b)Cu-1 mol%, Al-5 mol%, (c) Cu-2 mol%, Al-5 mol%, (d) Cu-3 mol%, Al-5 mol% co-doped ZnO nano structures.

Fig. 3. EDS spectra of (a) pure ZnO, (b)Cu-1 mol%, Al-5 mol%, (c) Cu-2 mol%, Al-5 mol%, (d) Cu-3 mol%, Al-5 mol% co-doped ZnO nano structures.

Photoluminescence Studies. The photoluminescence Excitation spectra and Emission spectra of the pure and co-doped ZnO nano particles recorded at room temperature with excitation wave length of 305 nm and measured at monitoring wavelength 467 nm are shown in Fig.4 and Fig. 5. In the emission spectra blue emission peaks appeared at 435 nm, 448 nm, 468 nm and 473 nm, the peak appeared at 492 nm corresponds to blue-green emission, the green emission band appeared from 527-550 nm centered at 536 nm and the band appeared from 583 nm to 624 nm centered at 608 nm, which corresponds to yellow, orange and red emission regions. The peaks appeared in the visible region may be attributed to the origin of defects such as oxygen vacancies and intrinsic defects in ZnO nano materials [22].Copper is a prominent luminescent activator of visible luminescence by constructing the localized states in the band gap of ZnO. The energy interval from zinc interstitial to zinc vacancy is of the order of 473 nm which corresponds to blue emission, also the prominent transitions observed at 468 nm, 448 nm corresponds to blue emission [1]. The green emission observed at 536 nm may be

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Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954

ascribed to the impurity levels corresponds to the singly ionized oxygen vacancy in ZnO nano particles [22, 23]. The green emission observed in the spectra confirmed the substitution of Cu in to the ZnO host lattice [23].

Fig. 4. RTPL Excitation and Emission Spectra of a) pure ZnO, (b)Cu-1 mol%, Al-5 mol%, (c) Cu-2 mol%, Al-5 mol%, (d) Cu-3 mol%, Al-5 mol% co-doped ZnO nano structures.

Fig. 5. RTPL Excitation and Emission Spectra of a) pure ZnO, (b)Cu-1 mol%, Al-5 mol%, (c) Cu-2 mol%, Al-5 mol%, (d) Cu-3 mol%, Al-5 mol% co-doped ZnO nano structures.

Summary. Pure and co-doped ZnO nanoparticles have been synthesized at room temperature with out using any capping agent. XRD pattern reveals that all the samples possess hexagonal wurtzite structure with out any secondary phases.SEM images shows the agglomeration of the particles, and

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Mechanics, Materials Science & Engineering, April 2017 – ISSN 2412-5954

EDS data indicate the incorporation of dopant elements Al, Cu into the ZnO nanoparticles. PL studies shows the defect related peaks in the visible region.

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Cite the paper P. Swapna, S. Venkatramana Reddy (2017). Structural and Photoluminescence Studies of (Cu, Al) Co-doped ZnO Nanoparticles. Mechanics, Materials Science & Engineering, Vol 9. doi:10.2412/mmse.77.36.550

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