Band gap narrowing of cadmium oxide powder by rare earth praseodymium doping
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Band gap narrowing of cadmium oxide powder by rare earth praseodymium doping H.-Y. He and J. Lu, Key Laboratory of Auxiliary Chemistry & Technology for Chemical Industry, Ministry of Education, Shaanxi University of Science and Technology, Xi'an 710021, China Address all correspondence to H.-Y. He at [email protected] (Received 13 November 2012; accepted 31 January 2013)
Abstract Rare earth Pr-doped cadmium oxide (CdO) powders with various Pr contents (0–2.0 at.%) were synthesized by a coprecipitation process and characterized by x-ray diffraction, field emission scanning electron microscopy, and UV-vis spectrophotometry. The experimental results indicate that Pr doping led to a decrease of average particle size and change of optical property. The CdO powder with Pr content 0.5 at.% show a maximum Eg decrease of about 3.6% and an absorbance increase of about 8.26%. This variation is explained by the available band gap narrowing models and variations in lattice parameter and density with Pr content.
Introduction Pure and metal-doped degenerate semiconductor cadmium oxide (CdO) has been used in a wide range of optoelectronic applications like transparent conducting oxide, solar cells, smart windows, and optical communications, as well as other type of applications such as IR heat mirrors and gas sensors, etc.[1–5] These applications are based on its (CdO) optical and electrical properties,[1,6–9] which could be controlled through doping with different types of metallic ions. It was observed that doping of CdO with some metallic ions of smaller radius than that of Cd2+, like In, Sn, Al, Sc, and Y, improved its electrical conduction properties, and increases its optical energy gap.[1,10–14] However, Dakhel[15] studied the possibility of controlling the optoelectrical properties of CdO through doping with rare earth ions Sm3+ because of smaller ionic radius than that of Cd2+ and found that Sm3+ ions doping obviously narrows optical band gap and increases conductivity by slight doping level of 0.4 at.%. He further found that Dy[15] and Ce[16] dopings have similar effects on the optoelectric properties of CdO. Recently, the potential doping candidates of the rare earth oxide Gd[17] and Li–Ni[18] in improvement of the optical and electrical properties of the CdO films have also been reported. Pr cation has radius near Cd cation. Tetravalent Pr4+ can also provide more carriers for n-type CdO semiconductor than other trivalent rare earth cations such as Nd3+, Sm3+, Gd3+, etc., and so conductivity can be expected to have increased more. Moreover, the efficient visible and infra-red emissions of Pr cation in some host materials are reported in previous literature.[19–23] However, the literature survey indicates that there is no report on optoelectrical properties of Pr-doped CdO materials. The aim of the present
work is to study the effects of Pr doping with different levels on the structural and optical properties of CdO powders for the first time.
Materials and methods The starting materials used were all analy
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